METHOD TO REDUCE OVERSHOOT IN A VOLTAGE REGULATING POWER SUPPLY

Abstract

A method for operating a system including a voltage regulating power supply includes sensing a local voltage on a first node of the system and a remote voltage on a second node of the system. The first node and the second node are in a conductive path coupled to a load of the system. The first node is closer to a power stage of the voltage regulating power supply than the second node. The second node is closer to the load than the first node. The method includes detecting a load release event based on the local voltage, the remote voltage, and at least one predetermined threshold value.

Claims

1. A method for operating a system including a voltage regulating power supply, the method comprising: sensing a local voltage on a first node of the system and a remote voltage on a second node of the system, the first node and the second node being in a conductive path coupled to a load of the system, the first node being closer to a power stage of the voltage regulating power supply than the second node, the second node being closer to the load than the first node; and detecting a load release event based on the local voltage, the remote voltage, and at least one predetermined threshold value.

2. The method as recited in claim 1 further comprising: in response to detection of the load release event, disabling a pulse-width modulated control signal provided to the power stage and enabling a circuit to sink energy from the voltage regulating power supply while the pulse-width modulated control signal is disabled.

3. The method as recited in claim 2 further comprising: after the pulse-width modulated control signal is disabled for a predetermined interval, enabling the pulse-width modulated control signal and disabling the circuit.

4. The method as recited in claim 3 further comprising: in response to detection of a dynamic voltage change event triggered by the load, disabling the pulse-width modulated control signal while the circuit is disabled.

5. The method as recited in claim 1 further comprising: generating a control signal based on the local voltage, the remote voltage, a slew rate of the remote voltage, and the at least one predetermined threshold value.

6. The method as recited in claim 5 wherein generating the control signal comprises comparing a difference between the local voltage and the remote voltage to a first predetermined threshold value of the at least one predetermined threshold value.

7. The method as recited in claim 6 wherein generating the control signal further comprises comparing the slew rate of the remote voltage to a second predetermined threshold value of the at least one predetermined threshold value.

8. The method as recited in claim 5 wherein the control signal is generated to switch from an active level to an inactive level after a predetermined time.

9. The method as recited in claim 1 wherein the load release event is caused by a processor powered by the voltage regulating power supply.

10. The method as recited in claim 1 wherein the voltage regulating power supply is a step-down converter.

11. A system comprising: a power stage of a voltage regulating power supply, the power stage being coupled between an input power supply node and a second power supply node, the power stage being responsive to a pulse-width modulated signal; an energy absorbing element coupled between an output of the power stage and the second power supply node; a circuit coupled to the output of the power stage and the second power supply node; a first node of the system and a second node of the system, the first node and the second node being in a conductive path coupled to a load, the first node being closer to the power stage than the second node, the second node being closer to the load than the first node; and a processing circuit configured to sense a local voltage on the first node and a remote voltage on the second node and to detect a load release event based on the local voltage and the remote voltage.

12. The system as recited in claim 11 wherein the processing circuit is further configured to disable the pulse-width modulated signal and enable the circuit to sink energy from the voltage regulating power supply while the power stage is disabled in response to detection of the load release event based on the local voltage and the remote voltage.

13. The system as recited in claim 11 wherein the processing circuit comprises a pulse width modulator configured to generate the pulse-width modulated signal.

14. The system as recited in claim 11 wherein the processing circuit comprises: a compensation circuit configured to sense the local voltage and the remote voltage on the second node, compare a difference between the local voltage and the remote voltage to a predetermined threshold level, and compare a slew rate of the remote voltage to a second predetermined threshold level.

15. The system as recited in claim 11 further comprising: a printed circuit board housing the power stage, the energy absorbing element, the processing circuit, the circuit, and the load.

16. The system as recited in claim 11 wherein the processing circuit is further configured to disable the pulse-width modulated signal in response to detection of a dynamic voltage change event triggered by the load based on the local voltage and the remote voltage, the circuit being disabled while the power stage is disabled.

17. The system as recited in claim 11 wherein the circuit includes a resistance coupled in parallel with a diode or low-side switch of the power stage.

18. The system as recited in claim 11 further comprising: the load including a processor powered by the voltage regulating power supply, wherein the load release event is caused by a working status change of the processor.

19. A processing system comprising: a processor coupled to an output voltage node; and a voltage regulating power supply comprising: a power stage coupled between an input power supply node and a second power supply node, the power stage being responsive to a pulse-width modulated signal; an energy absorbing element coupled between an output of the power stage and the second power supply node; a first node of the processing system and a second node of the processing system, the first node and the second node being in a conductive path coupled to a load, the first node being closer to the power stage than the second node, the second node being closer to the load than the first node; and a processing circuit configured to sense a local voltage on the first node and a remote voltage on the second node and to detect a load release event of the processor based on the local voltage and the remote voltage.

20. The processing system as recited in claim 19 wherein the processing circuit is further configured to disable the pulse-width modulated signal and enable the energy absorbing element to absorb energy from the voltage regulating power supply while the power stage is disabled in response to detection of the load release event based on the local voltage and the remote voltage.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The present invention may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings.

[0008] FIG. 1 illustrates a circuit diagram of a conventional voltage regulating power supply.

[0009] FIG. 2 illustrates signal waveforms for the conventional voltage regulating power supply of FIG. 1.

[0010] FIG. 3 illustrates a detailed signal waveform for the conventional voltage regulating power supply of FIG. 1.

[0011] FIG. 4 illustrates a circuit diagram of an embodiment of a voltage regulating power supply.

[0012] FIG. 5 illustrates a circuit diagram of a voltage regulating power supply consistent with at least one embodiment of the invention.

[0013] FIG. 6 illustrates a detailed signal waveform for the voltage regulating power supply of FIG. 5.

[0014] FIG. 7 illustrates an information and control flow for operating the voltage regulating power supply of FIG. 5 consistent with at least one embodiment of the invention.

[0015] The use of the same reference symbols in different drawings indicates similar or identical items.

DETAILED DESCRIPTION

[0016] Referring to FIG. 4, voltage regulating power supply 422 includes voltage regulator controller 402 that generates at least one pulse-width modulated signal CTL.sub.PWM for controlling one or more switches in power stage 408. In at least one embodiment, a pulse-width modulator 404 adjusts the duty cycle of pulse-width modulated signal CTL.sub.PWM according to information received from compensation circuit 406. Compensation circuit 406 senses the current provided to the load using feedback signals V.sub.OUT+ and V.sub.OUT−, and amplifier 414 generates a corresponding voltage signal indicative of the comparison. Voltage regulator controller 402 compares that voltage signal to predetermined reference voltage V.sub.REF. For example, that voltage signal is subtracted from predetermined reference voltage V.sub.REF. The difference between the indicator and the predetermined reference voltage V.sub.REF is modulated by modulator 416 and provided to pulse-width modulator control circuit 404. Pulse-width modulator control circuit 404 uses that signal to adjust the duty cycle of pulse-width modulated signal CTL.sub.PWM (e.g., to turn off pulse-width modulated signal CTL.sub.PWM) provided to power stage 408.

[0017] In at least one embodiment, pulse-width modulator 404 increases the duty cycle of pulse-width modulated signal CTL.sub.PWM in response to the sensed voltage being less than the predetermined reference voltage V.sub.REF and decreases the duty cycle of the control signal in response to the sensed voltage exceeding the predetermined reference voltage VREF. The predetermined reference voltage V.sub.REF has a value selected to provide a load system with output voltage V.sub.OUT that satisfies the voltage specification of a target application. In at least one embodiment, predetermined reference voltage V.sub.REF is provided to an integrated circuit for use in regulating the output voltage provided by the voltage regulating power supply to a load system.

[0018] In general, compensation circuit 406 senses the output voltage and compares the sensed output voltage to a predetermined threshold value to determine whether to increase or decrease the duty cycle of pulse-width modulated signal CTL.sub.PWM to maintain a stable output voltage. However, this topology has bandwidth limitations and is not fast enough to sufficiently reduce or eliminate the overshoot. Accordingly, additional capacitors are added to the system to absorb the excess energy. Those additional capacitors occupy area on the printed circuit board and increase the cost of a target system. In addition, compensation circuit 406 does not distinguish whether the voltage change is the result of the dynamic voltage change event triggered by the load or a load release event.

[0019] A technique reduces overshoot in the output voltage provided by a voltage regulating power supply (e.g., a buck converter). The voltage regulating power supply estimates printed circuit board impedance between an output of the voltage regulating power supply and a load by sensing a local voltage proximate to the output and a remote voltage proximate to the load. The local voltage is sensed on a local node closer to the output than a remote node corresponding to the remote voltage and the remote node is closer to the load than the local node. Parasitic impedance (e.g., printed circuit board parasitic impedance 410 and printed circuit board parasitic impedance 412) is coupled between the local node and the remote node due to routing on a printed circuit board required by mechanical specifications (e.g., minimum spacing between a processor and a voltage regulating power supply). The voltage regulating power supply uses the estimated impedance of the printed circuit board to generate a control signal that selectively enables a resistance that absorbs energy in response to a load release event, thereby reducing overshoot in output voltage of the voltage regulating power supply without needing additional capacitance to sink excess charge. In an embodiment, the resistance is coupled in parallel to a diode or transistor in a power stage of the voltage regulating power supply.

[0020] Referring to FIGS. 5 and 6, voltage regulating power supply 522 includes voltage regulator controller 502 that generates at least one pulse-width modulated signal CTL.sub.PWM for power stage 508. Voltage regulator controller 502 distinguishes between a load release event and a dynamic voltage change event (e.g., due to transition of a processor from a high-power state to an idle state when exiting a gaming program). The amount of voltage overshoot V.sub.OUT_OVERSHOOT over interval t is related to output capacitance C.sub.OUT of the voltage regulating power supply, slew rate K.sub.i.sub.load of load current i.sub.load, slew rate K.sub.i.sub.ind of inductor current i.sub.ind, and printed circuit board impedance R.sub.PCB over interval t. Since the overshoot voltage is related to the difference in the slew rate of the inductor current and since the slew rate of the load current and the slew rate of the inductor current is related to the parasitic printed circuit board impedance R.sub.PCB, estimating the parasitic printed circuit board impedance R.sub.PCB by sensing a voltage difference across the remote node and the local node is used to detect a load release event (e.g., a change in inductor current accompanied by a substantial change in load current) as distinguished from a dynamic voltage change event (e.g., a change in inductor current accompanied by a nominal change in load current). Note that if the voltage change is caused by a dynamic voltage change event and not a load release event, then the difference of difference of local voltage V.sub.OUT_L and remote voltage V.sub.OUT_R will not change dynamically. That is difference voltage V.sub.DIFF, which is equal to I.sub.LOAD×R.sub.PCB will be constant since parasitic printed circuit board impedance R.sub.PCB and the load current is constant.

[0021] In at least one embodiment of voltage regulating power supply 522, power stage 508 includes switched circuit 526, which includes a resistive path that is selectively enabled using control signal CTL.sub.2 generated by voltage regulator controller 502. Since the voltage change to a new level may be caused by a load release event (e.g., when a processor enters an idle mode from a higher power mode) or in response to a dynamic voltage change event (e.g., when software in the load processor changes a power state of the processor) that does not need to absorb as much excess energy, compensation circuit 506 detects the load release event as distinguished from a dynamic voltage change event. In at least one embodiment, voltage regulating power supply 522 detects the load release event as distinguished from a dynamic voltage change event and enables switched circuit 526 to absorb excess energy to reduce or eliminate the overshoot voltage at the output capacitors in response to the load release event.

[0022] Referring to FIGS. 5 and 7, in at least one embodiment of voltage regulating power supply 522, voltage regulator controller 502 estimates parasitic printed circuit board impedance R.sub.PCB between the power stage and the output node (702). For example, voltage regulator controller 502 senses local voltage V.sub.OUT_L and remote voltage V.sub.OUT_R+ and remote voltage V.sub.OUT_R−. Voltage regulator controller 502 uses remote voltage V.sub.OUT_R+ and remote voltage V.sub.OUT_R− to determine when the slew rate of remote voltage V.sub.OUT_R exceeds a predetermined voltage. For example, difference amplifier 514 compares remote voltage V.sub.OUT_R+ to remote voltage V.sub.OUT_R− and provides an indication thereof to evaluation circuit 524. In addition, voltage regulator controller 502 uses remote voltage V.sub.OUT_R+, remote voltage V.sub.OUT_R−, and local voltage V.sub.OUT_L to determine when difference voltage V.sub.DIFF (V.sub.DIFF=V.sub.OUT_L−V.sub.OUT_R+=R.sub.PCB×I.sub.LOAD) falls below a predetermined threshold voltage (i.e., estimated parasitic printed circuit board impedance R.sub.PCB falls below a predetermined value) to determine whether a load release event occurred. For example, difference amplifier 518 compares local voltage V.sub.OUT_L to remote voltage V.sub.OUT_R+ and provides an indication of the difference (e.g., difference voltage V.sub.DIFF) to evaluation circuit 524.

[0023] Evaluation circuit 524 compares difference voltage V.sub.DIFF to predetermined threshold voltage V.sub.TH. When difference voltage V.sub.DIFF is less than predetermined threshold voltage V.sub.TH and the slew rate of V.sub.OUT_R is greater than a predetermined reference voltage, then voltage regulator controller 502 detects a load release event and generation of overshoot at remote output node V.sub.OUT_R (704). Evaluation circuit 524 provides an indicator to pulse-width modulator 504 via modulator 516. Pulse-width modulator 504 disables one or more pulse-width modulated control signals CTL.sub.PWM that are provided to power stage 508 and enables control signal CTL.sub.2 to cause switched circuit 526 to absorb excess energy (706). The current flowing through the inductor flows to load 520 and the output capacitors discharge to load 520 and into the power stage (e.g., into a diode or a source of a low-side transistor). Switched circuit 526 absorbs excess energy, thereby reducing or eliminating voltage overshoot at load 520 during the load release event. After a predetermined time (e.g., after N cycles of a clock signal used by pulse-width modulator 504) during which pulse-width modulated control signal CTL.sub.PWM is disabled (e.g., a pulse-width modulated control signal provided to a high-side transistor in the power stage is set to a level that disables the high-side transistor) and switched circuit 526 is enabled, pulse-width modulator 504 disables switched circuit 526 and enables one or more pulse-width modulated control signals CTL.sub.PWM (708).

[0024] A slowly changing voltage V.sub.DIFF indicates that no high load release event occurred. As a result, even if the slew rate of V.sub.OUT_R is greater than the predetermined reference value V.sub.REF, voltage regulator controller 502 still detects a dynamic voltage change event. Evaluation circuit 524 provides an indictor to pulse-width modulator 504, which disables one or more pulse-width modulated control signals CTL.sub.PWM that are provided to power stage 508. During the dynamic voltage change event, switched circuit 526 remains disabled.

[0025] Thus, a technique for sensing overshoot of a voltage regulating power supply that absorbs excess energy in response to a load release event without increasing output capacitance has been disclosed. The description of the invention set forth herein is illustrative and is not intended to limit the scope of the invention as set forth in the following claims. For example, while the invention has been described in an embodiment in which switched circuit 526 is illustrated as being coupled in parallel to a low-side transistor of power stage 508, switched circuit 526 may be coupled to the power supply node in other locations sufficient to absorb energy to reduce the overshoot. In at least one embodiment, switched circuit 526 includes one or more resistors coupled in parallel with a low-side transistor of power stage 508. In other embodiments an internal break diode is used. In at least one embodiment rather than sense V.sub.OUT_L at the load side of inductor L, V.sub.OUT_L is sensed at a node internal to power stage 508. Note that predetermined threshold voltage V.sub.TH and predetermined reference value V.sub.REF can be selected by the user using conventional techniques. The terms “first,” “second,” “third,” and so forth, as used in the claims, unless otherwise clear by context, is to distinguish between different items in the claims and does not otherwise indicate or imply any order in time, location or quality. For example, “a first access,” and “a second access,” does not indicate or imply that the first access occurs in time before the second access. Variations and modifications of the embodiments disclosed herein may be made based on the description set forth herein, without departing from the scope of the invention as set forth in the following claims.