Startup of switched capacitor step-down power converter
11522447 · 2022-12-06
Assignee
Inventors
- Aichen Low (Cambridge, MA)
- Walid Fouad Mohamed Aboueldahab (Wokingham, GB)
- Gregory Szczeszynski (Hollis, NH)
Cpc classification
H02M3/07
ELECTRICITY
H02M1/0032
ELECTRICITY
H02M3/072
ELECTRICITY
H02M1/38
ELECTRICITY
H02M1/32
ELECTRICITY
H02M1/0025
ELECTRICITY
G05F1/565
PHYSICS
Y02B70/10
GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
International classification
H02M3/07
ELECTRICITY
Abstract
Circuit embodiments for a switched-capacitor power converter, and/or methods of operation of such a converter, that robustly deal with various startup scenarios, are efficient and low cost, and have quick startup times to steady-state converter operation. Embodiments prevent full charge pump capacitor discharge during shutdown of a converter and/or rebalance charge pump capacitors during a startup period before switching operation by discharging and/or precharging the charge pump capacitors. Embodiments may include a dedicated rebalancer circuit that includes a voltage sensing circuit coupled to an output voltage of a converter, and a balance circuit configured to charge or discharge each charge pump capacitor towards a target steady-state multiple of the output voltage of the converter as a function of an output signal from the voltage sensing circuit indicative of the output voltage. Embodiments prevent or limit current in-rush to a converter during a startup state.
Claims
1. A switched-capacitor power converter including: (a) first and second input terminals, and first and second output terminals; (b) a plurality of series-connected switches connected between the first input terminal and the first output terminal; (c) a plurality of charge pump capacitors, each connected between corresponding adjacent pairs of the plurality of series-connected switches; and (d) a controller coupled to the plurality of series-connected switches; wherein the controller is configured to reduce the rate of charge transfer between the plurality of charge pump capacitors by controlling the ON resistance R.sub.ON of the series-connected switches during a pre-switching period of a startup state of the switched-capacitor power converter.
2. The invention of claim 1, wherein the ON resistance R.sub.ON of the series-connected switches is controlled for at least one of a first selected duration of time, and/or for a first number of switching cycles, and/or while a first measured voltage across any of the plurality of charge pump capacitors is within a corresponding desired value range.
3. The invention of claim 1, wherein at least some of the plurality of series-connected switches includes a corresponding auxiliary switch/pathway having a higher ON resistance R.sub.ON than the corresponding series-connected switch, and wherein the controller is configured to increase the ON resistance RO.sub.N of the series-connected switches Sx by using the auxiliary switches/pathways in lieu of the corresponding switches.
4. The invention of claim 3, wherein the plurality of series-connected switches are switched at a selected frequency, and the controller is further configured to increase the frequency of switching during the pre-switching period of the startup state of the switched-capacitor power converter.
5. The invention of claim 4, wherein the increase the frequency of switching is increased for at least one of a second selected duration of time, and/or for a second number of switching cycles, and/or while a second measured voltage across any of the plurality of charge pump capacitors is within a corresponding desired value range.
6. The invention of claim 5, wherein the ON resistance R.sub.ON of the series-connected switches is controlled for at least one of a first selected duration of time, and/or for a first number of switching cycles, and/or while a first measured voltage across any of the plurality of charge pump capacitors is within a corresponding desired value range.
7. The invention of claim 1, wherein the plurality of series-connected switches each comprise a field-effect transistor (FET) having a gate that controls the ON resistance R.sub.ON of the FET, each FET configured to have its gate coupled to a source of gate drive voltage, and wherein the controller is configured to increase the ON resistance R.sub.ON of the series-connected switches by reducing the gate drive voltage to the respective gates of the FETs.
8. The invention of claim 7, wherein the plurality of series-connected switches are switched at a selected frequency, and the controller is further configured to increase the frequency of switching during the pre-switching period of the startup state of the switched-capacitor power converter.
9. The invention of claim 8, wherein the increase the frequency of switching is increased for at least one of a second selected duration of time, and/or for a second number of switching cycles, and/or while a second measured voltage across any of the plurality of charge pump capacitors is within a corresponding desired value range.
10. The invention of claim 9, wherein the ON resistance R.sub.ON of the series-connected switches is controlled for at least one of a first selected duration of time, and/or for a first number of switching cycles, and/or while a first measured voltage across any of the plurality of charge pump capacitors is within a corresponding desired value range.
11. The invention of claim 1, wherein the switched-capacitor power converter is configured as one of a boost power converter, a buck power converter, or a buck-boost power converter.
12. A switched-capacitor power converter including: (a) first and second input terminals and first and second output terminals; (b) a disconnect switch coupled to the first input terminal and configured to be coupled to a first voltage source; (c) a second voltage source coupled to the first and second output terminals, wherein a voltage across the second voltage source is less than a voltage across the first voltage source; (d) a charge pump coupled between the first and second input terminals and the first and second output terminals, the charge pump including a plurality of charge pump capacitors; (e) a controller coupled to the disconnect switch; wherein the controller is configured to open the disconnect switch in a startup mode of operation, thereby disconnecting the first voltage source from the charge pump and enabling operation of the charge pump in a step-up mode of voltage conversion until the plurality of charge pump capacitors are charged to at least a desired voltage, and thereafter to close the disconnect switch, thereby connecting the first voltage source to the charge pump and enabling operation of the charge pump in a step-down mode of voltage conversion.
13. The invention of claim 12, wherein the controller is configured to close the disconnect switch in a gradual manner to limit a current in-rush to the charge pump.
14. The invention of claim 12, wherein the controller is configured to provide an intermediate state between operation of the charge pump in the step-up mode and operation of the charge pump in the step-down mode in which charge pump operation is paused and then the disconnect switch is closed.
15. The invention of claim 12, wherein the disconnect switch provides bi-directional isolation.
16. The invention of claim 12, wherein the disconnect switch includes two series-connected FET switches having corresponding body diodes configured with opposite polarities.
17. A switched-capacitor power converter including: (a) first and second input terminals and first and second output terminals, wherein the first and second input terminals are coupled to a first voltage source; (b) a disconnect switch coupled to the first output terminal and configured to be coupled to a second voltage source; (c) a charge pump coupled between the first and second input terminals and the first and second output terminals, the charge pump including a plurality of charge pump capaci- tors; (d) a controller coupled to the disconnect switch; wherein the controller is configured to open the disconnect switch in a startup mode of operation, thereby disconnecting the second voltage source from the charge pump until the plurality of charge pump capacitors are charged from the first voltage source to at least a desired voltage level, and thereafter to close the disconnect switch, thereby connecting the second voltage source to the charge pump and enabling operation of the charge pump.
18. The invention of claim 17, wherein the controller is configured to close the disconnect switch in a gradual manner to limit a current in-rush to the charge pump.
19. The invention of claim 17, wherein the disconnect switch provides bi-directional isolation.
20. The invention of claim 17, wherein the disconnect switch includes two series-connected FET switches having corresponding body diodes configured with opposite polarities.
Description
DESCRIPTION OF THE DRAWINGS
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(27) Like reference numbers and designations in the various drawings indicate like elements.
DETAILED DESCRIPTION
(28) The present invention encompasses circuits and methods for reliable startup of switched-capacitor step-down power converters that robustly deal with all startup scenarios (including intermediate states), are efficient and low-cost, and have reasonably quick startup times to steady-state power converter operation.
(29) Charge Pump States
(30) In general, a switched-capacitor power converter or charge pump will operate in at least one of three distinct states: a steady-state, a shutdown state, and a startup state. During the steady-state or “normal” operation state, such a charge pump receives an input voltage V.sub.IN and transforms it, by switching connections to the pump capacitors Cx, into an output voltage V.sub.OUT that is a fraction of V.sub.IN. In the shutdown state, there is no charge pump switching activity. In the startup state, a voltage difference is presented across the input terminals of the charge pump and circuit activity is enabled to eventually cause the charge pump to begin switching in order to transfer charge from the voltage source at the input to the output voltage using the pump capacitors Cx—that is, to transition from the shutdown state to steady-state operation. In some embodiments of the present invention, the startup state may include a pre-switching period in which some circuitry in the charge pump is active (e.g., to rebalance capacitor nodes) but charge pump switching is disabled (where charge pump switching is defined as applying clock waveforms P1 and P2 as generated by controller 104 to control the charge pump switches S1-S9, collectively referred to as “Sx”), and a subsequent switching period in which charge pump switching commences but steady-state operation is not yet achieved.
(31) However, the voltage across each pump capacitor Cx relative to each other as well as to the voltage across the output capacitor C.sub.OUT may be such that in the first few switching cycles, the charge pump switches Sx may experience voltage stress and/or the in-rush current at the charge pump input and output terminals may be excessive. Accordingly, during the startup phase it may be necessary to first rebalance the voltage on the pump capacitors with respect to the voltage on the output capacitor (noting the output capacitor may comprise multiple individual capacitors).
(32) In particular, there is a problem of possible transient voltage stress across the charge pump switches Sx during start-up, when the pump capacitors Cx and the output capacitor C.sub.OUT are unbalanced relative to each other, meaning that they have non-zero voltages that deviate significantly from their steady-state values for particular V.sub.IN or V.sub.OUT values. Further, embodiments of switched-capacitor power converters may be subjected to a variety of capacitor charge states at startup resulting, for example, from startup of the power converter after a long shutdown duration and/or restart of the power converter after a fault condition (e.g., short circuit fault). For example, at startup of such a power converter after a long shutdown duration, none of the capacitors or capacitances C.sub.OUT or Cx may be initially precharged (Scenario 1). In other conditions prior to startup, the pump capacitors Cx (having a collective capacitance C.sub.PUMP) may have no charge (e.g., due to leakage) while the much larger capacitance C.sub.OUT remains precharged (Scenario 2). In still other conditions, such as a startup after a short across the converter load, the pump capacitors Cx may be precharged but C.sub.OUT may have discharged (Scenario 3). Intermediate conditions may also occur where C.sub.OUT and/or the pump capacitors Cx are at varying precharged and/or discharged degrees. A good converter design should be able to deal with all of these startup conditions.
(33) In Scenario 2 (precharged C.sub.OUT, non-precharged Cx), terminal V2+ and the stack-nodes V.sub.CX may by subjected to an over-voltage when the low-side phase switches S7, S8 are first enabled and during initial switching cycles. In Scenario 3 (non-precharged C.sub.OUT, pre-charged Cx), terminal V2+ and the stack-nodes V.sub.CX may also be subjected to an over-voltage in initial switching cycles when larger-voltage capacitors discharge into lower-voltage capacitors. Further, the ON resistance R.sub.ON of the FET-based switches may be as low as about 2 milliohms. With such low ON resistance in the charge pump switches, such startup conditions may result in damaging levels of current in-rush during initial switching cycles and over-voltage stress of the switches, particularly of FET (especially MOSFET) switches. In addition, FET-based switches generally need a gate drive circuit per switch, which may comprise at least a level shifter circuit and a transistor driver circuit. Large current in-rush and over-voltage stress may also readily damage the transistor driver circuit for one or more charge pump switches.
(34) A simplistic solution to dealing with an unknown startup charge state for a switched-capacitor power converter would be to discharge all capacitors before startup commences so as to result in a known charge state, or to use high-voltage rated FETs for the charge pump switches so as to mitigate FET over-voltage stress. However, this solution is inefficient, wastes charge (which may be highly undesirable for battery-powered applications), and requires longer startup times to steady-state power converter operation. Furthermore, a particular application, such as a cellular phone, may not tolerate or allow a power converter component to discharge the output capacitor C.sub.OUT at its own whim.
(35) A somewhat better solution is to utilize a precharge circuit to initially charge both the charge pump capacitors Cx and the output capacitor C.sub.OUT before startup. For example, if the pump capacitors C1-C4 in
(36) A more practical circuit embodiment of a switched-capacitor power converter and/or methods of operation of such a power converter should be able to robustly deal with all startup scenarios (including intermediate states), be efficient, low cost, and have quick startup times to steady-state converter operation. A number of solutions are presented below that may be used alone or in combination to achieve these desirable characteristics by preventing or minimizing in-rush current and/or avoiding switch over-stress. One solution category involves maintaining charge on pump capacitors or charging pump capacitors off of the output capacitor C.sub.OUT during the shutdown state and/or during a pre-switching period of the startup state. Another solution category is to rebalance charge or voltage on the pump capacitors during a pre-switching period of the startup state, or alternatively during a switching period of the startup state. Some of the rebalancing solutions involve dedicated circuitry, while other rebalancing solutions involve only slight circuit modifications and/or modifications of clock timing sequences applied to the charge pump switches Sx. Yet another solution category avoids rebalancing while achieving the same robustness goal by reducing the rate of charge transfer at startup. Still another solution category avoids rebalancing while achieving the same robustness goal by selectively isolating the charge pump input or output terminals during a pre-switching period of the startup state.
(37) A. Prevention of In-Rush Current by Phase Node Pull-Down
(38) One aspect of the invention encompasses embodiments that avoid or mitigate a sudden or uncontrolled in-rush current at startup by preventing or limiting a full discharge of the charge pump capacitors Cx during shutdown of a power converter. Shutdown may occur, for example, to conserve battery life of a hand-held electronic device such as a cellular telephone. Such embodiments address the issues of Scenario 2 (precharged C.sub.OUT, non-precharged Cx), meaning that some voltage is available at terminal V2+ while there is little to no voltage across the pump capacitors Cx. Each of the circuits and methods described in this section alleviate the problems of startup over-voltage in Scenario 2 by preventing or limiting an in-rush of current from the output capacitor C.sub.OUT towards each pump capacitor Cx when switching begins. It is this in-rush of current that may cause over-voltage stress on the stack-nodes V.sub.CX.
(39) In a conventional shutdown state for the example embodiment shown in
(40) In some cases, it may not be feasible to keep switches S7 and S8 closed (ON) during the shutdown state, such as may be the case where the respective drivers for controlling the state of switches S7 and S8 are powered by a supply voltage that is not available in the shutdown state. Alternative embodiments cope with such a limitation. For example,
(41) For example, the pulldown devices 302a, 302b may be simple resistors having resistive values small enough to support charging of capacitors C1-C4 while large enough to minimize power loss when phase nodes PN1, PN2 switch during post-startup steady-state operation. Such resistors may have fixed values, or be variable in value, or have a value set at the time of manufacture. Suitable resistive values for resistor-based pulldown devices 302a, 302b for many applications may be 100-200Ω. Since resistor-only pulldown devices 302a, 302b are always connected in the circuit, they are able to prevent charge pump capacitor discharge during the shutdown state without requiring any supply voltages.
(42) In some applications, using only resistors for the pulldown devices 302a, 302b may hurt light-load efficiency due to the power loss when phase nodes PN1, PN2 are switched during steady-state operation. In alternative embodiments, the pulldown devices 302a, 302b may be transistor-based devices that are enabled (made fully or partially conductive) during a shutdown state and/or a pre-switching period of a startup state but which may be disabled (made essentially non-conductive) during steady-state operation so as to reduce or eliminate the impact of their presence on the charge pump 300. For example, the pulldown devices 302a, 302b may be resistive transistors (including MOSFETs), variable-resistance transistors (including MOSFETs), segmented transistors (including MOSFETs), transistor-based current sinks, etc. If a supply voltage is available during the shutdown state, the pulldown devices 302a, 302b may be enabled during the shutdown state and/or before charge pump switching is first enabled (i.e., during a pre-switching period of the startup state), but disengaged at other times, such as during steady-state operation. If a supply voltage is not available during the shutdown state, the pulldown devices 302a, 302b may be enabled during just the pre-switching period, but disengaged at other times, such as during steady-state operation.
(43) In any case, when the pulldown devices 302a, 302b are engaged, they slowly (compared to low-side phase switches S7, S8) pull down the phase nodes PN1, PN2 coupled to the bottom terminals of the pump capacitors Cx towards circuit ground (i.e., the potential at V2−). If the pulldown devices 302a, 302b are engaged during the shutdown state, the charge pump capacitors Cx will not fully discharge relative to the voltage at terminal V2+. If the pulldown devices 302a, 302b are not engaged during the shutdown state but are engaged during the pre-switching period of the startup state, the charge pump capacitors Cx may fully discharge during the shutdown state but will gently charge off of the voltage at terminal V2+ through the inherent body-diodes D2-D5 during the pre-switching period of the startup state at a reduced rate. Either approach avoids or minimizes the magnitude of the in-rush of current from C.sub.OUT towards the pump capacitors Cx when the low-side phase switches S7, S8 are enabled at the start of charge pump switching. In some embodiments, if the pulldown devices 302a, 302b are engaged while in the pre-switching period, the voltage at the phase nodes PN1, PN2 may be monitored so that the pulldown devices 302a, 302b can be disengaged (disabled/disconnected) once the phase nodes PN1, PN2 are pulled close to ground; thereafter, the switches S7 and S8 can be turned ON and switched until steady-state operation is reached.
(44) In variant embodiments, the pulldown devices 302a, 302b may be a binary switch FET in series with an impedance, such as a resistor. For example,
(45) In general, there need be only one switched pulldown device 302x per phase node PNx. However, in some cases (for example, if separate phase node connections per pump capacitor are implemented for various reasons, such as to facilitate die or board layout), the switched pulldown device 302x of
(46) For pulldown devices 302a, 302b that include a switch, the state of the pulldown devices 302a, 302b during the shutdown state and/or the pre-switching period may be controlled by suitably programming or configuring the controller 104. The pulldown devices 302a, 302b may be regarded as “soft” pulldown devices for the resistive or current-controlled manner in which the devices pull down on the phase nodes PNx. In contrast, switches S7 and S8 have very low ON resistance and will pull down the phase nodes PNx very strongly (“hard”) when closed (ON).
(47) It should be noted that the circuits and methods described in this section for pulling down the phase nodes PNx may be used in conjunction with the circuits and methods described below.
(48) B. Rebalancing Solutions
(49) 1. Dedicated Rebalancer Circuit
(50) One aspect of the invention encompasses embodiments that rebalance charge pump capacitors during a pre-switching period of the startup state before switching begins. Rebalancing involves setting the voltage across each of the charge pump capacitors Cx (e.g., C1-C4 in
(51) One approach to rebalancing charge pump capacitors in a switched-capacitor step-down converter is to use a dedicated rebalancer circuit. For example,
(52) Embodiments of the rebalancer circuit 402 may comprise one or more subcircuits. For example,
(53) In
(54) In this example, the input voltage to the current mirror circuit 506 is supplied by V.sub.IN to the switched-capacitor power converter. The example current mirror circuit 506 includes four mirroring legs comprising FETs M1-M4 having respective sources coupled to V.sub.IN, respective drains coupled to corresponding resistors R1-R4, and respective gates coupled to the drain and gate of FET M.sub.M (and thus to the drain of FET M0). In operation, V.sub.OUT is sensed by the differential amplifier 504 and a reference current I.sub.REF is produced through FET M0 and FET M.sub.M equal to the voltage at the input of the differential amplifier 504 divided by R0: I.sub.REF=xV.sub.OUT/R0, where xV.sub.OUT is proportional to V.sub.OUT by the ratio 1/(n+1) and n is the scaling factor for resistor nR.
(55) The reference current I.sub.REF is proportional to V.sub.OUT, and is mirrored in each of the mirroring legs, in known fashion. The mirror current in each of the mirroring legs generates a corresponding voltage set by the value of the corresponding resistors R1-R4. Thus, in this example, R1 should be set such that I.sub.REF×R1 ideally equals 4×V.sub.OUT at a node connected to stack-node V.sub.C1, which is the “top” plate of capacitor C1 (see
(56) The rebalancer circuit 500 of
(57) Note that while the switched pulldown resistor circuit 580 (as well as the switched pulldown device 302x of
(58) Referring back to
(59) In the embodiment illustrated in
(60) While the rebalancer circuit 500 may be used on a timed basis, a robust and fast-acting embodiment preferably includes active voltage balance comparison circuits to measure and balance the voltages at the stack-nodes V.sub.CX, either simultaneously or sequentially For example, instances of the balancing comparator 590 of
(61) In operation, when the rebalancer circuit 402 is engaged during the pre-switching period of the startup state of a charge pump and the process of charging/discharging starts, the respective balancing comparators 590 compare the voltage at the stack-nodes V.sub.CX (representing the voltage across the pump capacitors Cx) to xV.sub.OUT. In one example embodiment, each balancing comparator 590 is configured to require that the voltage across its respective pump capacitor Cx is within a desired range (e.g., 80% to 120%) of the target value in order to generate an “in range” FLAG output (which may be a logic “high” or “low” as needed for the logic control circuitry). The desired range may be set, for example by changing the division ratios of the resistors nR and mR, such as by setting or adjusting the value of resistor mR.
(62) The FLAG outputs of the balancing comparators 590 can be used as inputs to logic control circuitry that determines when all capacitors satisfy the specified “in range” condition, upon which the voltage balancing process is stopped and the startup state transitions from the pre-switching period to the subsequent switching period in which charge pump switching commences but steady-state operation is not yet achieved. For example, the rebalancer circuit 500 may be disabled by opening switches Sw0-Sw4 in
(63) One advantage of using balancing comparators 590 over a timed rebalancing sequence is that the switched-capacitor power converter does not have to wait for the worst-case RC time constants inherent in both the rebalancer circuit 402 and converter circuit 102 to ensure that the pump capacitors Cx are voltage balanced. This saves on the startup and recovery time if restarting a converter circuit 102 into intermediate conditions (e.g., C.sub.OUT and/or C.sub.PUMP are at varying precharged and/or discharged degrees) between Scenario 1, 2, or 3.
(64) For robustness, it is useful to configure the rebalancer circuit 500 to cope with atypical states that may arise in particular applications, such as the case of a short circuit across the load terminals where C.sub.OUT becomes fully discharged (note that restarting a switched-capacitor power converter after a short circuit would be similar to starting up in Scenario 3). In the case of a short circuit where the output voltage V.sub.OUT is close to or at circuit ground, then I.sub.REF, which is generated from V.sub.OUT, may be insufficient for proper operation of the rebalancer circuit 500. Accordingly, it is useful to provide an offset current that is enabled when a short circuit is detected and/or when V.sub.OUT is less than a desired level sufficient to generate an adequate value for I.sub.REF.
(65) Referring to
(66) If a short circuit condition is detected, switch Sw is closed, and an offset current I.sub.OFFSET will be generated by the current source 510 and applied to the first input of the differential amplifier 504, thereby skewing the voltage normally generated by applying V.sub.OUT to the voltage divider comprising series-connected resistors nR and R. Once the short circuit condition ends or is deemed to end (e.g., with V.sub.OUT having a value above the level defining the “short circuit condition”, or after a period of time), then switch Sw may be opened again. A minor drawback of including the switchable offset current circuit 508 is that an offset may be created in the target voltage for the pump capacitors Cx, meaning that the pump capacitors Cx may not be ideally balanced. However, the offset will be limited and short circuit conditions normally should be infrequent. An alternative implementation to the switchable offset current circuit 508 that accomplishes a similar outcome is to introduce a systematic or preferential offset within the differential amplifier 504 itself, so that the output of the differential amplifier 504 generates an adequate value for I.sub.REF even while the output voltage V.sub.OUT is close to or at circuit ground (i.e., the short circuit condition). One way to introduce such an offset within the differential amplifier 504 is to skew the sizes of transistors/devices used within the differential amplifier 504, in known fashion.
(67) As should be appreciated, the current mirror circuit 506 may have fewer or more mirroring legs for switched-capacitor power converters of different conversion ratios. In addition, for a multi-phase power converter, some or all of the mirroring legs may be duplicated for connection to a different phase. In some applications, one or more of the mirror leg resistors (e.g., R1-R4) may be variable to accommodate switched-capacitor power converters that can be configured to have different conversion ratios (e.g., divide-by-2 or divide-by-3). One such power converter is described in U.S. Pat. No. 10,263,514, issued Apr. 16, 2019, entitled “Selectable Conversion Ratio DC-DC Converter”, assigned to the assignee of the present invention and hereby incorporated by this reference.
(68) The rebalancer circuit 402 of
(69) In this example, the supply voltage to the current mirror circuit 606 is supplied by the input voltage V.sub.IN to a coupled switched-capacitor converter circuit. The example current mirror circuit 606 includes one mirroring leg comprising FET M.sub.P1 having its source coupled to V.sub.IN and its drain coupled to series-connected resistors R1-R3. The series-connected resistors R1-R3 are in turn coupled to circuit ground. The voltage sensing subcircuit 602, current mirror circuit 606, and series-connected resistors R1-R3 can be considered to comprise a bias generator 608.
(70) V.sub.OUT is sensed by the differential amplifier 604 and a reference current I.sub.REF is produced through FET M0 and FET M.sub.P0 that is equal to the voltage at the input of the differential amplifier 604 divided by R0: I.sub.REF=V.sub.OUT/R0. The reference current I.sub.REF is directly proportional to V.sub.OUT, and is mirrored in the mirroring leg, in known fashion. The mirror current in the mirroring leg generates a set of corresponding voltages determined by the values of the resistors R1-R3. Thus, in this example, R1-R3 should be set such that I.sub.REF×(R1+R2+R3) ideally equals 4×V.sub.OUT at a node n1. Similarly, R2-R3 should be set such that I.sub.REF×(R2+R3) ideally equals 3×V.sub.OUT at a node n2; R3 should be set such that I.sub.REF×R3 ideally equals 2×V.sub.OUT at a node n3. Thus, the generated voltages at the nodes nx are each a multiple of the output voltage V.sub.OUT of the coupled converter circuit. Alternate methods of generating voltages at the nodes nx from the sensed output voltage V.sub.OUT are possible and include using operational amplifiers or voltage multipliers (not shown).
(71) The voltages at the nodes nx and the output voltage V.sub.OUT are coupled to rebalance drivers 610a-610d, which are in turn are connected to corresponding stack-nodes V.sub.CX, which are the “top” plates of respective pump capacitors Cx (see
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(73) The output node of the voltage buffer is coupled to an enable/disable switch Sw.sub.D, which in turn is coupled to a stack-node V.sub.CX. When rebalancing is needed during a pre-switching period of the startup state, switch Sw.sub.D is enabled (closed). Once rebalancing is completed and charge pump switching begins, Sw.sub.D is disabled (opened) to isolate the voltage buffer from the stack-node V.sub.CX.
(74) When switch Sw.sub.D is enabled (closed), the voltage generated at node nx, buffered by the rebalance driver 610x, charges a corresponding pump capacitor Cx from V.sub.IN through FET M.sub.N if the voltage across the pump capacitor Cx is lower, and otherwise provides a discharge path to V.sub.OUT through FET M.sub.P if the voltage across the pump capacitor Cx is higher. An alternate embodiment of rebalancer driver 610x may have the drain terminal of FET M.sub.P coupled to circuit ground instead of V.sub.OUT. While this alternate embodiment accomplishes a similar discharging function when needed, the charge removed from the pump capacitor is wasted and cannot be recouped.
(75) If the voltage offsets V.sub.OS1, V.sub.OS2 are not used, the voltage buffer still works except that the buffer output voltage will end up below the voltage at node nx (by an amount approximately equal to the FET M.sub.N threshold voltage) when precharge is predominant through N-type FET M.sub.N, and above the voltage at node nx (by an amount approximately equal to the FET M.sub.P threshold voltage) when discharge is predominant through P-type FET M.sub.P. The voltage offsets V.sub.OS1, V.sub.OS2 may be omitted in applications where the threshold voltage error is tolerable.
(76) Note that the rebalance driver 610d for stack-node V.sub.C4 node in
(77) One advantage of the rebalancer circuit 600 of
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(79) When the first switch Sw.sub.CHG is enabled (closed) while the second switch Sw.sub.DIS is disabled (opened), the first current source I1 charges a corresponding pump capacitor Cx whose top plate is connected to an associated stack-node V.sub.CX. Conversely, when the first switch Sw.sub.CHG is disabled (opened) while the second switch Sw.sub.DIS is enabled (closed), the second current source I2 discharges a corresponding pump capacitor Cx whose top plate is connected to the associated stack-node V.sub.CX. Whether or not a charging or discharging function is needed for a particular pump capacitor Cx can be determined by first comparing each stack-node voltage V.sub.CX and the output voltage V.sub.OUT, for example, by using the balancing comparator 590 of
(80) More generally, an advantage of the dedicated rebalancer circuit 402 is that, even when the stack-nodes V.sub.CX and/or V.sub.OUT have voltages close to zero, the rebalancer circuit 402 does not get stuck or waste time going through unnecessary rebalancing, thereby reducing startup time. Using a dedicated rebalancer circuit 402 to rebalance the voltages across the pump capacitors Cx can prevent over-stress of the charge pump switches (including transistors in corresponding driver circuits) upon startup from a wide variety of initial conditions. In some embodiments, only one core cell of the rebalancer circuit 402 (e.g., voltage sensing subcircuit 502 and current mirror circuit 506 in
(81) 2. Rebalancing of Charge Pump Capacitors During a Pre-Switching Period
(82) Another aspect of the invention encompasses embodiments that rebalance charge pump capacitors during a pre-switching period of the startup state (i.e., before charge pump switching begins) by repurposing existing switches or existing switch pathways within the charge pump, thereby reducing design complexity and area.
(83) For example, when rebalancing the step-down converter circuit 200 of
(84) In some embodiments of charge pumps, such as the example shown in
(85) In charge pump embodiments having auxiliary switches/pathways SxA, one technique for rebalancing charge pump capacitors during a pre-switching period of a startup state involves using the existing auxiliary switches/pathways SxA and specialized initialization switch timing sequences to precharge or discharge the charge pump capacitors Cx based on the scenario presented. Beneficially, this technique requires no new charge pump circuit pathways, but only selection of a set of clock timing sequences based on a measurement of the voltages across the charge pump capacitors Cx (i.e., the voltages at the stack-nodes V.sub.CX). The voltages may be measured, for example, by instances of the balancing comparator 590 of
(86) For example,
(87) In this example, auxiliary switches/pathways S7A and S8A are used in lieu of the separate switched pulldown devices 302x shown in
(88) Time t.sub.1 can be implemented as a fixed duration after time t.sub.0 or as a variable duration based on when the phase-nodes PN1, PN2 are detected to have reached a voltage sufficiently close enough to the voltage at the V2− terminal of the charge pump 300, and/or when the pump capacitors Cx are detected to have been charged sufficiently off of the C.sub.OUT capacitor. Note that in Scenario 1, the duration between time t.sub.0 and time t.sub.1 is most likely short to the point of being relatively unnecessary given the relatively low voltage level across the C.sub.OUT capacitor to begin with. Therefore, it is possible to skip or omit this precharging step of enabling auxiliary switches/pathways S7A and S8A between time t.sub.0 and time t.sub.1. Furthermore, since the voltages across the pump capacitors Cx (i.e., the voltages at the stack-nodes V.sub.CX) are all low as well, and often sufficiently close to the voltage across C.sub.OUT, either phase-node “soft” pulldown or rebalancing in Scenario 1 is not always needed and may be skipped.
(89) The pre-switching period ends at t.sub.1 and charge pump switching begins at time t.sub.5 as shown in
(90) The period from time t.sub.1 to time t.sub.5 may be part of the switching period of the startup state in which charge pump switching may commence but steady-state operation is not yet achieved. The duration from time t.sub.1 to time t.sub.5 is application dependent, but may be, for example, how long it takes to decide to bypass the rebalancing process. Depending on the implementation, time t.sub.5 could overlap with time t.sub.1 (i.e., time t.sub.1 and time t.sub.5 occur at the same time), or there can be a delay from time t.sub.1 to time t.sub.5 less than or equal to the charge pump period, which is the inverse of the charge pump switching frequency (technically, the delay can be greater than the charge pump period as well, although this then adds to the overall startup time of the charge pump). Note also that the omission of intermediate time point labels between time t.sub.1 and time t.sub.5 is only so that the labels for time points t.sub.1 and t.sub.5 match up with the like-named time points in
(91) As another example,
(92) Beginning at time t.sub.1, auxiliary switches/pathways S1A-S3A, S5A are all closed (more generally, auxiliary switches/pathways S1A-S.sub.mA except S.sub.m-1A would all be closed at time t.sub.1, where m is the number of series-connected switches between the V1+ and V2+ charge pump terminals). After time t.sub.1, the (m−1) selected auxiliary switches/pathways are progressively opened in reverse order relative to terminal V1+ (S3A to S1A, in the illustrated example) over several time periods. In the illustrated example, in reverse order, auxiliary switches/pathways S3A to S1A are progressively opened from time t.sub.3 to time t.sub.5. Notably, the auxiliary switch/pathway S5A is kept closed throughout this initialization phase, thus keeping the charge pump capacitor C4 connected in parallel with the output capacitor C.sub.OUT. Accordingly, for the present example, when all auxiliary switches/pathways S1A-S3A are all closed from time t.sub.1 to time t.sub.3, a voltage source coupled to terminal V1+ will precharge pump capacitors C1-C3. At time t.sub.3, auxiliary switch/pathway S3A is opened, and charge pump capacitor C3 ceases to charge. At time t.sub.4, auxiliary switch/pathway S2A is opened, and charge pump capacitor C2 ceases to charge. Finally, at time t.sub.5, auxiliary switch/pathway S1A is opened, and charge pump capacitor C1 ceases to charge. Also at time t5, auxiliary switch/pathway S5A is opened, and charge pump capacitor C4 ceases to be charged by the output capacitor C.sub.OUT. At or after time t.sub.5, switched operation following clock waveforms P1 and P2 can commence (the dotted timing pulse lines after time t.sub.5 indicate that the auxiliary switches/pathways S1A-S3A, S5A may be switched to follow the state of respective primary switches S1-S3, S5 or kept open). Note that the omission of an intermediate time point label between time t.sub.1 and time t.sub.3 is only so that the labels for time points t.sub.1 and t.sub.3-t.sub.5 match up with the like-named time points in
(93) Time points t.sub.3, t.sub.4, and t.sub.5 may be fixed by a timing circuit (not shown), or may be determined by adaptive time periods initiated after time t.sub.1, taking into account the values of each charge pump capacitor C1-C4, the ON resistance of auxiliary switch/pathways S1A-S3A, S5A, as well as the voltage levels at each stack-node V.sub.C1-V.sub.C4 relative to the voltage level at the Vx node. Alternatively, the voltage levels at each stack-node V.sub.C1-V.sub.C4 (i.e., the voltage levels across each charge pump capacitor C1-C4) may be monitored throughout times t.sub.1-t.sub.5, using circuits like voltage or current comparators or instances of the balancing comparator 590 of
(94) For example, referring to
(95) An alternate embodiment that implements timing diagram 720 involves using a different set of auxiliary switches/pathways that connect between each stack-node V.sub.CX and the V1+ terminal. However, while this alternate embodiment provides flexibility regarding the order in which each auxiliary switch/pathway may be opened between time t.sub.1 to time t.sub.5, each auxiliary switch/pathway may no longer be in parallel with an existing primary switch Sx, thereby introducing new pathways that add complexity and require secondary ESD protection schemes.
(96) Since one goal of the pre-switching period is to precharge the charge pump capacitors Cx to target voltage levels, it becomes apparent that closing first and second “low-side” phase switches S7 and S8 throughout times t.sub.1-t.sub.5 is necessary.
(97) While the timing diagram 720 shows that the auxiliary switches/pathways S1A-S3A, S5A are set to an ON state continuously during particular time periods from time t.sub.1 to time t.sub.5, in alternative embodiments the auxiliary switches/pathways S1A-S3A, S5A may be pulsed ON and OFF during those time periods to avoid excessive power/thermal dissipation. Note also that the deadtime between opening and closing of all switches is not shown for clarity, but that some deadtime may be needed to avoid momentary connections that may cause undesired charging or discharging of the pump capacitors Cx.
(98) As yet another example,
(99) Beginning at time t.sub.1, auxiliary switches/pathways S2A-S5A are all closed, and then progressively opened in forward order relative to terminal V1+ (S2A to S5A, in the illustrated example) from time t.sub.2 to time t.sub.5 (more generally, auxiliary switches/pathways S2A-SmA would all be closed at time t.sub.1, where m is the number of series-connected switches between the V1+ and V2+ charge pump terminals). Notably, switches S1 and S1A (if present) are kept open through the initialization phase, thus isolating the charge pump capacitors from the V.sub.IN voltage at terminal V1+. Accordingly, for the present example, when the auxiliary switches/pathways S2A-S5A are all closed from time t.sub.1 to time t.sub.2, the charge pump capacitors C1-C4 will discharge into the output capacitor C.sub.OUT that is coupled to the Vx node. At time t.sub.2, auxiliary switch/pathway S2A is opened and charge pump capacitor C1 ceases to discharge. At time t.sub.3, auxiliary switch/pathway S3A is opened and charge pump capacitor C2 ceases to discharge. At time t.sub.4, auxiliary switch/pathway S4A is opened and charge pump capacitor C3 ceases to discharge. Finally, at time t.sub.5, auxiliary switch/pathway S5A is opened and charge pump capacitor C4 ceases to discharge. At time t.sub.5, switched operation following clock waveforms P1 and P2 can commence (the dotted timing pulse lines after time t.sub.5 indicate that the auxiliary switches/pathways S2A-S5A may be switched to follow the state of respective switches S2-S5, or kept open).
(100) As with the example shown in
(101) An alternate embodiment that implements timing diagram 740 involves using a different set of auxiliary switches/pathways that connect between each stack-node V.sub.CX to the Vx node. However, while this alternate embodiment provides flexibility regarding the order in which each auxiliary switch/pathway may be opened between time t.sub.1 to time t.sub.5, each auxiliary switch/pathway may no longer be in parallel with an existing primary switch Sx, thereby introducing new pathways that add complexity and require secondary ESD protection schemes.
(102) Yet another embodiment that implements timing diagram 740 involves using a different set of auxiliary switches/pathways that connect between each stack-node V.sub.CX to circuit ground at the V2− terminal. In addition to sharing the disadvantages of complexity and ESD secondary protection, this method is also more wasteful since each charge pump capacitor Cx is discharged to ground rather than transferring its charge to the output capacitor C.sub.OUT.
(103) More generally, an advantage of this invention compared to the dedicated rebalancer circuit 402 lies in its simplicity, area efficiency, and reduced ESD risk. The voltages across the pump capacitors Cx can be rebalanced similarly to prevent over-stress of the charge pump switches (including transistors in corresponding driver circuits) upon startup from a wide variety of initial conditions. This aspect of the invention achieves this by repurposing existing switches or existing switch pathways within the charge pump 300, thereby eliminating the need for a rebalancer circuit 402.
(104) 3. Rebalancing Capacitors by Decoupling from Input Voltage Source
(105) Yet another aspect of rebalancing charge pump capacitors in a switched-capacitor step-down power converter at startup involves running the converter backwards as a step-up converter for a selected time, and then reverting to step-down operation. This method works best when starting up from Scenario 2 (precharged C.sub.OUT, non-precharged Cx), and if the output capacitor C.sub.OUT is sufficiently large to minimize any V.sub.OUT voltage droop that could occur during step-up operation.
(106)
(107) For startup, the converter circuit 102 can be configured to operate in a step-up mode by making the voltage V.sub.OUT across the output capacitor C.sub.OUT be the power source of the converter circuit 102, rather than the voltage source 106 (noting that many charge pump designs can operate in step-up mode by changing where the voltage source is applied). Accordingly, during startup, the disconnect switch S.sub.Dis1 is set to an open state to disconnect the voltage source 106 from the converter circuit 102, leaving only the voltage V.sub.OUT across the output capacitor C.sub.OUT as a power source for the converter circuit 102. Switched operation following clock waveforms P1 and P2 can commence, causing charge transfer from the output capacitor C.sub.OUT through the pump capacitors Cx, towards the V1+ terminal of the converter circuit 102. The duration of this initial startup state can be determined, for example, by measuring the voltages at the stack-nodes V.sub.CX as described above, or by setting a pre-determined time duration. Once the pump capacitors Cx are suitably charged to their steady-state voltages (in this case, multiples of the voltage V.sub.OUT), the disconnect switch S.sub.Dis1 is closed, thereby reconfiguring the converter circuit 102 to operate in a step-down mode by reconnecting the voltage source 106 to the converter circuit 102. Accordingly, the converter circuit 102 reverts to step-down operation from the startup step-up mode. Note that a brief intermediate state may be introduced between initial reverse step-up mode and normal forward step-down operation where charge pump switching is paused and then the disconnect switch S.sub.Dis1 is closed. This intermediate state may be skipped or omitted as long as the disconnect switch S.sub.Dis1 can be closed in a gradual manner to minimize voltage transients or in-rush current at the V1+ terminal. It should also be noted that the disconnect switch S.sub.Dis1 may be entirely omitted if the presence or connection of voltage source 106 across the V1+, V1− charge pump terminals can be sequenced together with the startup of converter circuit 102. For instance, the voltage source 106 can be disconnected from the converter circuit 102 or made to be high impedance in the shutdown state. When the converter circuit 102 is enabled, the voltage source 106 can remain disconnected or high impedance while the converter circuit 102 begins startup in reverse step-up mode. At the end of this initial startup state in step-up mode, the voltage source 106 can then be connected to the converter circuit 102 or made low impedance for the remainder of startup as well as for steady-state operation as a step-down converter. More generally, an advantage of this invention is that pump capacitor rebalancing takes place without requiring a dedicated rebalancer circuit 402 or specialized switch timing sequences during a pre-switching period of the startup state.
(108) C. Reducing the Rate of Charge Transfer at Startup
(109) A novel technique that achieves robust startup of a charge pump under a variety of startup scenarios involves commencing switching of the charge pump by the P1 and P2 clock waveforms right at the beginning of startup (i.e., without any pre-switching period or other initialization phase) and in step-down mode, but with a reduced rate of charge transfer per switching cycle, and therefore a reduced rate of voltage change at each of the V.sub.CX stack-nodes (see
(110) For example,
(111) The ON resistance R.sub.ON of the series-connected charge pump switches (e.g., S1-S5) may be controlled by temporarily using the corresponding auxiliary switches/pathways SxA, each of which has a higher ON resistance R.sub.ON than the corresponding primary switch Sx, for a selected duration of time or number of switching cycles in lieu of the primary switches Sx. A segmented FET may be used to implement an auxiliary pathway SxA; utilizing only one or a few (less than all) segments results in a higher effective R.sub.ON for a segmented FET. An auxiliary switch SxA may also be a separate smaller FET connected in parallel with a corresponding primary switch Sx and configured to have a higher ON resistance R.sub.ON than the corresponding primary switch Sx. The selection of the auxiliary switches/pathways SxA in lieu of the primary switches Sx to increase R.sub.ON (block 908) may be controlled by suitably programming or configuring the controller 104.
(112) Alternatively, or in addition, the ON resistance R.sub.ON of the series-connected charge pump switches may be increased by reducing the FET gate-drive voltage for those switches for a selected duration of time and/or number of switching cycles (which is also a measure of time). The FET gate-drive voltage can be controlled by suitably programming or configuring the controller 104.
(113) The duration of increased R.sub.ON for the series-connected charge pump switches may be set by a fixed or variable timing circuit (not shown), or may be determined by one or more factors, including pump capacitor voltages, V.sub.IN, V.sub.OUT, and V.sub.CX (i.e., the voltages at the stack-nodes V.sub.CX), and the size of the capacitors (e.g., C1-C4 and/or C.sub.OUT). For example, referring to
(114) In addition to temporarily increasing the ON resistance R.sub.ON, the frequency of charge pump switching (e.g., the frequency of clock waveforms P1 and P2) may be increased for all or part of the duration of increased R.sub.ON. Thereafter, the frequency of charge pump switching can revert to a normal value for power efficiency. For example, a normal clock frequency for P1 and P2 for many applications may be in the range of about 100 kHz to about 1 MHz. While the R.sub.ON of the series-connected charge pump switches is temporarily increased, the clocking frequency may also be increased, for example, by a factor of 2 or more. The increased clock frequency reduces the rate of voltage change at each of the V.sub.CX stack-nodes until the problem of possible in-rush current is eliminated or mitigated. The frequency of charge pump switching may be controlled by suitably programming or configuring the controller 104.
(115) In the special case of a single-phase symmetric cascade multiplier like the circuits of
(116) A benefit of the above techniques is that they may be implemented using only existing control and charge pump circuitry. Further, such techniques may be intelligently applied by measuring the stack-node voltages V.sub.CX to determine which startup scenario applies, allowing selection of the best corresponding solution. However, selection and application of such techniques may be done independently of the startup scenario for some applications, if desired.
(117) D. Startup with Decoupling from Output Voltage Source
(118) Another method of robustly starting up a switched-capacitor step-down converter from a variety of startup scenarios is to add a switch between the output of the converter circuit 102 and the voltage V.sub.OUT across the output capacitor C.sub.OUT. This method eliminates the need for rebalancing. For example,
(119) As with the example shown in
(120) Optionally, an intermediate capacitor C.sub.VX may be coupled across the output terminals V2+, V2− of the converter circuit 102 between the switch block 1002 and the converter circuit 102, for example, if noise/EMI needs to be filtered or if there exists circuitry powered off node V.sub.X. The voltage across the intermediate capacitor C.sub.VX is Vx, and the capacitance of the intermediate capacitor C.sub.VX generally would be set to be much smaller than the capacitance of the output capacitor C.sub.OUT and smaller than the capacitance of each charge pump capacitor Cx (e.g., C.sub.VX may equal about 10% of each charge pump capacitor).
(121) During shutdown and startup, the disconnect switch S.sub.Dis2 is set to an open state to disconnect the converter circuit 102 from the output capacitor C.sub.OUT and the output load 108. In this example, the shutdown configuration allows the discharge of the stack-nodes V.sub.CX and hence of the charge pump capacitors Cx without discharging the output capacitor C.sub.OUT and thus without affecting the load 108. The discharge of the stack-nodes V.sub.CX may be implemented using auxiliary switches/pathways SxA that connect from each stack-node V.sub.CX and V.sub.X to ground. With the stack-nodes V.sub.CX, Vx discharged and in light of the small size of the intermediate capacitor C.sub.VX, the switched-capacitor power converter 1000 shown in
(122) In many applications, it may be useful to close a disconnect switch S.sub.Dis2 in a gradual manner to prevent a large current in-rush or out-rush through the switches Sx of the converter circuit 102 while the voltages across the intermediate capacitor C.sub.VX and the output capacitor C.sub.OUT equalize. Gradual closing of the disconnect switch S.sub.Dis2 may be time-based or may be a function of measured current through the disconnect switch S.sub.Dis2.
(123)
(124) In a first startup example, the voltage regulator 1102 is disabled initially, isolating the output voltage V.sub.OUT from terminal V2+ of the converter circuit 102. The converter circuit 102 may then be switched in normal fashion (i.e., clock waveforms P1 and P2 are applied) until the charge pump capacitors Cx reach desired voltages (fractions of the input voltage V.sub.IN).Thereafter, the voltage regulator 1102 is enabled and automatically handles any voltage difference between V.sub.X and V.sub.OUT, in known fashion, so as to set and regulate V.sub.OUT to a desired level.
(125) In a second startup example, the voltage regulator 1102 is enabled at the same that converter circuit 102 begins switching according to clock waveforms P1 and P2. The voltage regulator 1102 also automatically controls and regulates V.sub.OUT while handling any voltage difference between V.sub.X and V.sub.OUT, in known fashion.
(126)
(127) In the illustrated example, switch S.sub.A is series-connected between the positive input terminal and an inductor L, and switch S.sub.C is series-connected between the positive output terminal and the inductor L. Switch S.sub.B is coupled in a shunt configuration to a node N1 between switch S.sub.A and the inductor L. Switch S.sub.D is coupled in a shunt configuration to a node N2 between switch S.sub.C and the inductor L. When fabricated as MOSFET transistors, switches S.sub.A-S.sub.D have respective inherent body-diodes D.sub.A-D.sub.D as shown in
(128) A controller 1202, which may be internal to or external to the voltage regulator 1102, controls the operation of each of the switches S.sub.A-S.sub.D (control line connections to the switches S.sub.A-S.sub.D are omitted to avoid clutter). In particular, the controller 1202 may provide non-overlapping clock phases p1, p2 to the switches S.sub.A-S.sub.D (clock phases p1, p2 may have a different phasing than the two-phase clock waveforms P1 and P2 described previously for the converter circuit 102), although additional clock phases to the switches S.sub.A-S.sub.D are also possible. The voltage regulator 1102 may be effectively disabled by opening at least switches S.sub.A and S.sub.C.
(129) In various embodiments, the voltage regulator 1102 may include a subset of or all of the four switches S.sub.A-S.sub.D shown, implementing either a buck voltage converter (just switches S.sub.A, S.sub.B), a boost voltage converter (just switches S.sub.C, S.sub.D), or a non-inverting buck-boost voltage converter (all of switches S.sub.A-S.sub.D). For purposes of generality, all of the switches S.sub.A-S.sub.D will be considered present, although some may be forced closed (and thus function as a short circuit) for some configurations while others may be forced open for other configurations. However, it should be understood that embodiments of the voltage regulator 1102 may actually omit some of the switches S.sub.A-S.sub.D if only specific functionality is required.
(130) In the illustrated embodiment, the controller 1202 may configure the voltage regulator 1102 to operate in different modes of operation (however, in general, the voltage regulator does not have to be reconfigurable).
(131) For example, the voltage regulator 1102 may be configured to operate in a buck mode by closing switch S.sub.C while opening S.sub.D during every switching cycle. Switch S.sub.A will transition between ON and OFF states based on the duty cycle or ON-time of one of the clock phases (e.g., p1) as set by the controller 1202. Switch S.sub.B will transition between OFF and ON states that are complementary to the ON and OFF states of switch S.sub.A based on the other of the clock phases (e.g., p2). Non-reconfigurable implementations of the voltage regulator 1102 omit switch S.sub.D and replace switch S.sub.C with a direct connection to the positive output terminal, thereby reducing the component count and required integrated circuit area.
(132) As another example, the voltage regulator 1102 may be configured to operate in a boost mode by closing switch S.sub.A while opening switch S.sub.B during every switching cycle. Switch S.sub.D will transition between ON and OFF states based on the duty cycle or ON-time set by the controller 1202. Switch S.sub.C will transition between OFF and ON states that are complementary to the ON and OFF states of switch S.sub.D. Non-reconfigurable implementations of the voltage regulator 1102 omit switch S.sub.B and replace switch S.sub.A with a direct connection to the positive input terminal, thereby reducing the component count and required integrated circuit area.
(133) As yet another example, the voltage regulator 1102 may be configured to operate in a non-inverting buck-boost mode. In this type of configuration, all of the switches S.sub.A-S.sub.D transition between ON and OFF states, some at the same time and some at different times, during specific clock phases set by the controller 1202.
(134) In all configurations of the voltage regulator 1102, the controller 1202 sequences transitions of all the switches S.sub.A-S.sub.D in such a way as to incorporate any necessary clock phase or dead-time needed during operation of the switches S.sub.A-S.sub.D according to buck mode, boost mode, or buck-boost mode, in known fashion.
(135) Based on information indicative of the operational state of the switched-capacitor power converter 1100 in
(136) Benefits
(137) The methods and devices described herein are designed so that a switched-capacitor power converter can robustly startup from a variety of startup scenarios involving the initial voltage conditions of both the charge pump capacitors Cx and the output capacitor C.sub.OUT, and to do so in a reasonably quick startup time.
(138) It should clear to one of ordinary skill in the art that a number of the above solutions may be used in conjunction. For example, the circuits and methods described herein for prevention of charge pump capacitor full discharge during shutdown can be combined with the circuits and methods described herein for rebalancing charge pump capacitors before startup.
(139) Methods
(140) Another aspect of the invention includes methods of preventing charge pump capacitor full discharge during a shutdown state of a switched-capacitor power converter. For example,
(141)
(142) Additional aspects of the above method may include one or more of the following: wherein at least one of the plurality of pulldown devices is a resistor; wherein at least one of the plurality of pulldown devices is a transistor-based device, and further including configuring the transistor-based device to be at least partially conductive during at least one selected state of the power converter, and essentially non-conductive in at least one other state of the power converter; and/or wherein at least one of the plurality of pulldown devices is a switched pulldown device including a transistor-based switch in series with a resistor or a transistor-based current sink.
(143) Another aspect of the invention includes startup methods of rebalancing a plurality of charge pump capacitors in a switched-capacitor power converter and/or limiting in-rush current to such charge pump capacitors, and/or preventing over-stress of the charge pump switches.
(144) As another example,
(145) As still another example,
(146) As yet another example,
(147) As another example,
(148) Additional aspects of the above method may include one or more of the following: progressively opening at least some of the m auxiliary switches/pathways of the n series-connected switches Sx in reverse order; or progressively opening at least some of the m auxiliary switches/pathways of the n series-connected switches Sx in forward order.
(149) Additional aspects of the above method may include one or more of the following: wherein at least some of the plurality of series-connected switches Sx includes a corresponding auxiliary switch/pathway SxA having a higher ON resistance R.sub.ON than the corresponding switch Sx, further including increasing the ON resistance R.sub.ON of the series-connected switches Sx by using the auxiliary switches/pathways SxA in lieu of the corresponding switches Sx; wherein the plurality of series-connected switches Sx each comprise a field-effect transistor (FET) having a gate that controls the ON resistance R.sub.ON of the FET, each FET configured to have its gate coupled to a source of gate drive voltage, further including increasing the ON resistance R.sub.ON of the series-connected switches Sx by reducing the gate drive voltage to the respective gates of the FETs; and/or increasing the frequency of switching of the switches Sx for a second selected duration of time and/or a second number of switching cycles and/or until a second measured voltage across any of the plurality of charge pump capacitors is within a corresponding desired value range.
(150)
(151) Additional aspects of the above method may include one or more of the following: selectively connecting the plurality of charge pump capacitors to circuit ground through a resistive path during a pre-switching period; selectively connecting the plurality of charge pump capacitors to circuit ground after a pre-switching period; generating a reference current as a function of the generated signal indicative of the output voltage, and providing to each stack-node a corresponding multiple of the output voltage of the converter in response to the reference current; sensing an output voltage of the converter includes coupling an amplifier circuit to the output voltage of the converter, further including generating a reference current as a function of the generated signal indicative of the output voltage, and providing an offset current to the comparator (or inserting an offset within the comparator) when the output voltage is insufficient to generate an adequate value for the reference current; wherein charging or discharging each charge pump capacitor can occur through a plurality of rebalance drivers, each rebalance driver coupled to a corresponding stack-node and to a voltage derived from the generated signal indicative of the output voltage and configured to provide a charge path to the corresponding stack-node and/or a discharge path from the corresponding stack-node to one of the output voltage of the converter or circuit ground.
(152) Fabrication Technologies & Options
(153) The term “MOSFET”, as used in this disclosure, includes any field effect transistor (FET) having an insulated gate whose voltage determines the conductivity of the transistor, and encompasses insulated gates having a metal or metal-like, insulator, and/or semiconductor structure. The terms “metal” or “metal-like” include at least one electrically conductive material (such as aluminum, copper, or other metal, or highly doped polysilicon, graphene, or other electrical conductor), “insulator” includes at least one insulating material (such as silicon oxide or other dielectric material), and “semiconductor” includes at least one semiconductor material.
(154) As used in this disclosure, the term “radio frequency” (RF) refers to a rate of oscillation in the range of about 3 kHz to about 300 GHz. This term also includes the frequencies used in wireless communication systems. An RF frequency may be the frequency of an electromagnetic wave or of an alternating voltage or current in a circuit.
(155) Various embodiments of the invention can be implemented to meet a wide variety of specifications. Unless otherwise noted above, selection of suitable component values is a matter of design choice. Various embodiments of the invention may be implemented in any suitable integrated circuit (IC) technology (including but not limited to MOSFET structures), or in hybrid or discrete circuit forms. Integrated circuit embodiments may be fabricated using any suitable substrates and processes, including but not limited to standard bulk silicon, silicon-on-insulator (SOI), and silicon-on-sapphire (SOS). Unless otherwise noted above, embodiments of the invention may be implemented in other transistor technologies such as bipolar, LDMOS, BCD, GaAs HBT, GaN HEMT, GaAs pHEMT, and MESFET technologies. However, embodiments of the invention are particularly useful when fabricated using an SOI or SOS based process, or when fabricated with processes having similar characteristics. Fabrication in CMOS using SOI or SOS processes enables circuits with low power consumption, the ability to withstand high power signals during operation due to FET stacking, good linearity, and high frequency operation (i.e., radio frequencies up to and exceeding 50 GHz). Monolithic IC implementation is particularly useful since parasitic capacitances generally can be kept low (or at a minimum, kept uniform across all units, permitting them to be compensated) by careful design.
(156) Voltage levels may be adjusted, and/or voltage and/or logic signal polarities reversed, depending on a particular specification and/or implementing technology (e.g., NMOS, PMOS, or CMOS, and enhancement mode or depletion mode transistor devices). Component voltage, current, and power handling capabilities may be adapted as needed, for example, by adjusting device sizes, serially “stacking” components (particularly FETs) to withstand greater voltages, and/or using multiple components in parallel to handle greater currents. Additional circuit components may be added to enhance the capabilities of the disclosed circuits and/or to provide additional functionality without significantly altering the functionality of the disclosed circuits.
(157) Circuits and devices in accordance with the present invention may be used alone or in combination with other components, circuits, and devices. Embodiments of the present invention may be fabricated as integrated circuits (ICs), which may be encased in IC packages and/or modules for ease of handling, manufacture, and/or improved performance. In particular, IC embodiments of this invention are often used in modules in which one or more of such ICs are combined with other circuit blocks (e.g., filters, passive components, and possibly additional ICs) into one package. The ICs and/or modules are then typically combined with other components, often on a printed circuit board, to form an end product such as a cellular telephone, laptop computer, or electronic tablet, or to form a higher level module which may be used in a wide variety of products, such as vehicles, test equipment, medical devices, etc. Through various configurations of modules and assemblies, such ICs typically enable a mode of communication, often wireless communication.
(158) Conclusion
(159) A number of embodiments of the invention have been described. It is to be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, some of the steps described above may be order independent, and thus can be performed in an order different from that described. Further, some of the steps described above may be optional. Various activities described with respect to the methods identified above can be executed in repetitive, serial, or parallel fashion.
(160) It is to be understood that the foregoing description is intended to illustrate and not to limit the scope of the invention, which is defined by the scope of the following claims, and that other embodiments are within the scope of the claims. In particular, the scope of the invention includes any and all feasible combinations of one or more of the processes, machines, manufactures, or compositions of matter set forth in the claims below. (Note that the parenthetical labels for claim elements are for ease of referring to such elements, and do not in themselves indicate a particular required ordering or enumeration of elements; further, such labels may be reused in dependent claims as references to additional elements without being regarded as starting a conflicting labeling sequence).