BATTERY CHARGING WITH CHARGE CURRENT THROTTLING TO ASSIST MINIMUM SYSTEM VOLTAGE REGULATION

Abstract

A battery charger is provided that includes a switching power converter that regulates an output voltage on an output voltage rail. A transistor couples between the output voltage rail and a rechargeable battery for a system. An error amplifier controls the conductance of the transistor based upon a difference between a battery current conducted by the transistor to the battery and a battery current threshold. A pulse width modulator controls a duty cycle of the switching power converter responsive to a selected error signal from a group of error signals. Based upon which error signal is selected for the duty cycle control, the battery charger either increases or decreases the battery current threshold to assist in keeping the output voltage above a minimum system voltage for the system.

Claims

1. A switching power converter controller, comprising: a pulse width modulator configured to control a duty cycle of a switching power converter responsive to a selection from a group of error signals including an input voltage error signal based upon an error in an input voltage to the switching power converter, an input current error signal based upon an error in an input current to the switching power converter, and an output voltage error signal based upon an error in an output voltage of the switching power converter; a battery current error amplifier configured to generate a battery current error signal based upon a difference between a battery current and a battery current threshold, wherein the battery current error amplifier is further configured to control a conductance of a transistor responsive to the battery current error signal to control a magnitude of the battery current; and a battery current throttle circuit configured to increase the battery current threshold responsive to the selection of the output voltage error signal by the pulse width modulator to control the duty cycle of the switching power converter.

2. The switching power converter controller of claim 1, wherein the battery current throttle circuit comprises: a counter configured to adjust a count responsive to the selection from the group of error signals, wherein the counter is further configured to increase the count responsive to the selection of the output voltage error signal by the pulse width modulator to control the duty cycle of the switching power converter; and a digital-to-analog-converter configured to convert the count into the battery current threshold.

3. The switching power converter controller of claim 2, wherein the count is further configured to increase the count until a maximum count is reached responsive to the selection of the output voltage error signal by the pulse width modulator to control the duty cycle of the switching power converter, and wherein the digital-to-analog-converter is further configured to convert the maximum count so that the battery current threshold equals a reference battery current threshold.

4. The switching power converter controller of claim 2, wherein the counter is further configured to decrement the count responsive to the selection of the input voltage error signal by the pulse width modulator to control the duty cycle of the switching power converter.

5. The switching power converter controller of claim 2, wherein the counter is further configured to decrement the count responsive to the selection of the input current error signal by the pulse width modulator to control the duty cycle of the switching power converter.

6. The switching power converter controller of claim 5, wherein the counter is further configured to stop a decrement of the count responsive to the count being equal to zero.

7. The switching power converter controller of claim 2, wherein the switching power converter is a DC/DC switching power converter.

8. The switching power converter controller of claim 7, wherein the DC/DC switching power converter is a buck converter.

9. The switching power converter controller of claim 2, further comprising: a multiplexer configured to select between the output voltage and a battery voltage to provide a selected voltage; and an output voltage error amplifier configured to generate the output voltage error signal responsive to the difference between the selected voltage and a voltage threshold.

10. A method, comprising: controlling a duty cycle of a switching power converter responsive to a selection from a group of error signals including an input voltage error signal based upon an error in an input voltage to the switching power converter, an input current error signal based upon an error in an input current to the switching power converter, and an output voltage error signal based upon an error in an output voltage of the switching power converter; controlling a conductance of a transistor based upon a difference between a battery current and a battery current threshold to regulate the battery current; and adjusting the battery current threshold based upon the selection from the group of error signals to control the duty cycle of the switching power converter.

11. The method of claim 10, further comprising: incrementing a count responsive to a selection of the output voltage error signal for the controlling of the duty cycle of the switching power converter; and converting the count in a digital-to-analog converter to form the battery current threshold.

12. The method of claim 11, further comprising: decrementing the count responsive to a selection of the input voltage error signal for the controlling of the duty cycle of the switching power converter.

13. The method of claim 11, further comprising: decrementing the count responsive to a selection of the input current error signal for the controlling of the duty cycle of the switching power converter.

14. The method of claim 12, further comprising: selecting between an output voltage of the switching power converter and a battery voltage to provide a selected voltage; and generating the output voltage error signal responsive to a difference between an output voltage threshold and the selected voltage.

15. The method of claim 12, wherein controlling the duty cycle of a switching power converter comprising controlling the duty cycle of a buck converter.

16. A battery charger, comprising: a switching power converter configured to generate an output voltage on an output voltage rail; a transistor coupled to the output voltage rail and configured to conduct a battery current; a pulse width modulator configured to control a duty cycle of the switching power converter responsive to a selection from a group of error signals including an input voltage error signal based upon an error in an input voltage to the switching power converter, an input current error signal based upon an error in an input current to the switching power converter, and an output voltage error signal based upon an error in the output voltage; a battery current error amplifier configured to control a conductance of the transistor based upon a difference between the battery current and a battery current threshold; and a battery current throttle circuit configured to decrease the battery current threshold responsive to a selection of the input voltage error signal by the pulse width modulator to control the duty cycle of the switching power converter.

17. The battery charger of claim 16, wherein the battery current throttle circuit is further configured to decrease the battery current threshold responsive to a selection of the input current error signal by the pulse width modulator to control the duty cycle of the switching power converter.

18. The battery charger of claim 17, wherein the battery current throttle circuit is further configured to increase the battery current threshold responsive to a selection of the output voltage error signal by the pulse width modulator to control the duty cycle of the switching power converter.

19. The battery charger of claim 18, wherein the battery current throttle circuit comprises: a counter configured to increment a count responsive to the selection of the output voltage error signal by the pulse width modulator to control the duty cycle of the switching power converter, wherein the counter is further configured to decrement the count responsive to a selection of the input current error signal or the input voltage error signal by the pulse width modulator to control the duty cycle of the switching power converter; and a digital-to-analog-converter configured to convert the count to form the battery current threshold.

20. The battery charger of claim 18, further comprising: a multiplexer configured to select between the output voltage and a battery voltage to provide a selected voltage; and an output voltage error amplifier configured to generate the output voltage error signal responsive to the difference between the selected voltage and a voltage threshold.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0018] In the figures, like reference numerals designate corresponding parts throughout the different views.

[0019] FIG. 1 is a diagram of a conventional battery charger with a series regulator feedback loop.

[0020] FIG. 2 is a waveform diagram for the battery charger of FIG. 1 during a battery charging procedure.

[0021] FIG. 3 is a diagram of a conventional battery charger with a shunt regulator feedback loop.

[0022] FIG. 4 illustrates some operating waveforms of the battery charger of FIG. 1 during the QB REG operating region.

[0023] FIG. 5 illustrates an improved battery charger in accordance with an aspect of the disclosure.

[0024] FIG. 6 illustrates some operating waveforms for the improved battery charger of FIG. 5 during a first scenario in which there is a sudden demand in the output current I.sub.SYS while the battery current I.sub.BAT is being regulated to a default level.

[0025] FIG. 7 illustrates some operating waveforms for the improved battery charger of FIG. 5 during a second scenario in which the battery current I.sub.BAT changes in the presence of a load current (I.sub.SYS).

[0026] FIG. 8 illustrates some operating waveforms for the improved battery charger of FIG. 5 during a third scenario in which the system current (I.sub.SYS) gradually increases while the battery is being charged.

[0027] Embodiments of the present disclosure and their advantages are best understood by referring to the detailed description that follows. It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures.

DETAILED DESCRIPTION

[0028] An improved battery charger is provided that includes a DC/DC switching power converter that provides an output voltage to a system through an output power rail. A transistor couples between the output power rail and a rechargeable battery for the system. The system also includes a battery current throttle to control the conductance of the transistor. The battery current throttle controls a digital code such as a count from a counter that is converted by a digital-to-analog converter (DAC) to produce a battery reference current. A battery current error amplifier controls the conductance of the transistor to throttle (reduce) a battery current conducted by the transistor to the rechargeable battery to prevent or reduce the likelihood of the output voltage from reducing below a minimum system voltage level.

[0029] An example improved battery charger 500 is shown in FIG. 5. As discussed with regard to charger 100, a DC/DC switching power converter 105 such as a buck converter or a buck/boost converter regulates an output voltage V.sub.SYS and a load current I.sub.SYS carried on an output power rail 106 to power a system 150. System 150 includes a re-chargeable battery 145 that couples to output power rail 106 through a transistor QBAT 140. An auxiliary battery current error amplifier 135 may control the conductance of QBAT 140 based upon an error signal that is proportional to a difference between a battery current I.sub.BAT and a battery current threshold I.sub.BAT_ref. System 150 may be any application with a re-chargeable battery 145 such as a mobile device, a wearable device, or an internet-of-things device. Depending upon the conductance of the QBAT transistor 140, an output current I.sub.OUT from DC/DC switching power converter 105 is split into the load current I.sub.SYS to system 150 and the battery current I.sub.BAT.

[0030] An AC/DC switching power converter (not illustrated) such as a flyback converter may rectify an AC mains voltage to function as an input power source to DC/DC switching power converter 105. With respect to receiving this input power, DC/DC switching power converter 105 has a variable input resistance as represented by a resistance R.sub.IN. Input resistance R.sub.IN produces an ohmic drop on an output voltage V.sub.IN_TX_RX from the AC/DC switching power converter to produce an input voltage V.sub.IN to DC/DC switching power converter 105. The input voltage V.sub.IN is lower than the output voltage V.sub.IN_TX_RX by a product of the input resistance R.sub.IN and an input current I.sub.IN to DC/DC switching power converter 105. To regulate the input voltage V.sub.IN so that the input voltage V.sub.IN does not droop below a minimum input voltage threshold, charger 500 includes an input voltage error amplifier (EA_V.sub.IN) 125 that produces an input voltage error signal responsive to a difference between the input voltage V.sub.IN and an input voltage threshold V.sub.IN_ref. To regulate the input current I.sub.IN so that the input current I.sub.IN does not exceed a maximum input current, charger 100 includes an input current error amplifier (EA_I.sub.IN) 130 that produces an input current error signal responsive to a difference between an input current threshold I.sub.IN_ref and the input current I.sub.IN.

[0031] To regulate a battery voltage V.sub.BAT for battery 145 or the output voltage V.sub.SYS provided to system 150, battery charger 100 (which may also be denoted as a power adapter 100) includes an output voltage error amplifier (EA_V.sub.OUT) 120. Depending upon the selection in a multiplexer 155 to provide a selected voltage, the output voltage error amplifier 120 compares either the battery voltage V.sub.BAT or the output voltage V.sub.SYS to a voltage threshold V.sub.OUT_ref to produce an output voltage error signal. The output voltage error signal is proportional to the difference between the voltage threshold V.sub.OUT_ref and the selected voltage from multiplexer 155.

[0032] A battery current error amplifier 115 generates a battery current error signal EA_I.sub.BAT based upon a difference between the battery current I.sub.BAT and the battery current threshold I.sub.BAT_ref. A pulse width modulation (PWM) modulator 510 may then control the duty cycle (d) of a power switch (not illustrated) in DC/DC switching power converter 105 responsive to a selected one of the output voltage error signal, the input current error signal, the input voltage error signal, and the battery current error signal. PWM modulator 510 may thus regulate the duty cycle of the power switch in any given switching cycle based upon one of the error signals from the four error amplifiers 115, 120, 125, and 130. During the initial stages of charging battery 145, the output voltage V.sub.SYS is regulated to equal the minimum value V.sub.SYS_MIN. During these initial stages, multiplexer 155 thus selects for the output voltage V.sub.SYS and PWM modulator 510 adjusts the power switch duty cycle based upon the output voltage error signal accordingly. During this time, note that PWM modulator 510 cannot then respond to the battery current error signal from error amplifier 115. To allow charger 500 to continue to regulate the battery current I.sub.BAT despite the regulation of the output voltage V.sub.SYS to equal the minimum system voltage V.sub.SYS_MIN during the initial battery charging stages, charger 500 includes the auxiliary battery current error amplifier 135 that produces an auxiliary battery current error signal for the battery current I.sub.BAT responsive to a difference between the battery current I.sub.BAT and the battery current threshold I.sub.BAT_ref. Depending upon the value of the auxiliary battery current error signal, auxiliary error amplifier 135 regulates the conductance of the QBAT transistor 140 to regulate the battery current I.sub.BAT. In this fashion, charger 500 may simultaneously regulate the output voltage V.sub.SYS and the battery current I.sub.BAT while the output voltage V.sub.SYS is regulated to equal V.sub.SYS_MIN.

[0033] Note that the QBAT transistor 140 functions as a resistance to convert the system voltage V.sub.SYS into the battery voltage V.sub.BAT (and also the battery current I.sub.BAT). The regulation of the battery current I.sub.BAT by the control of the conductance of QBAT 140 by the auxiliary error amplifier 135 is thus effectively in series with respect to the regulation of the system voltage V.sub.SYS. This is an important advantage for battery charger 500 as the feedback control of the battery current I.sub.BAT is thus substantially decoupled from the feedback control of the output voltage V.sub.SYS. Despite this same advantage for conventional battery charger 100, the output voltage V.sub.SYS was subjected to droops below the minimum system voltage as discussed with regard to FIG. 4.

[0034] To prevent or reduce such droops in the output voltage V.sub.SYS, charger 500 is configured to increase or decrease the battery current threshold I.sub.BAT_ref through a battery current throttle circuit 505 depending upon which error signal pulse width modulator 510 uses to control the duty cycle of the switching power converter 105. A combinational logic circuit 515 may be configured to determine which error signal is used by pulse width modulator 510 to control the duty cycle of switching power converter 105. For example, the assertion of an EA_I.sub.BAT_IN_CTRL signal indicates to combinational logic circuit 515 that pulse width modulator 510 is currently controlling the duty cycle based upon the battery current error signal EA_I.sub.BAT from error amplifier 115. Similarly, the assertion of an EA_V.sub.OUT_IN_CTRL signal indicates to combinational logic circuit 515 that pulse width modulator 510 is currently controlling the duty cycle based upon the output voltage error signal EA_V.sub.OUT from output voltage error amplifier 120. In the same fashion, the assertion of an EA_V.sub.IN_CTRL signal indicates to combinational logic circuit 515 that pulse width modulator 510 is currently controlling the duty cycle based upon the input voltage error signal EA_V.sub.IN from input voltage error amplifier 125. Finally, the assertion of an EA_I.sub.IN_IN_CTRL signal indicates to combinational logic circuit 515 that pulse width modulator 510 is currently controlling the duty cycle based upon the input current error signal EA_I.sub.IN from input current error amplifier 130.

[0035] Based upon which error signal (and thus feedback loop) is in control of the duty cycle, combinational logic circuit 515 adjusts a count of an up-down counter 520. The count may be designated as an I.sub.BAT DAC code. A digital-to-analog converter 530 converts the count (the I.sub.BAT DAC code) from up-down counter 520 to produce the battery current threshold I.sub.BAT_ref. To control the count (and thus control the battery current threshold I.sub.BAT_ref), combinational logic circuit 515 may assert a count up signal to force up-down counter 520 to increment the count. Conversely, combinational logic circuit 515 may assert a count down signal to force up-down counter to decrement the count. A reset signal resets the count to a default value whereas a count stop signal stops any incrementing or decrementing of the count.

[0036] To assist in the control of the count, pulse width modulator 510 may also assert a current limit active signal when a current limit is active in switching power converter 105. In addition, a comparator 535 may assert a transient response signal should the output voltage VSYS fall below a system under voltage threshold V.sub.SYS_under_th. Combinational logic circuit 515 may respond to the assertion of the transient response signal V.sub.SYS_UNDER by comparator 535 with an assertion of the reset signal so that up-down counter 520 resets the count to a pre-defined level, which assists in the recovery of the output voltage V.sub.SYS.

[0037] In one implementation, combinational logic circuit 515 may decrement the count by one code of its dynamic range if the EA_V.sub.OUT_IN_CTRL signal is zero (a binary false state) and one of the following conditions is satisfied: the EA_I.sub.IN_IN_CTRL signal is one (a binary true state), the EA_V.sub.IN_IN_CTRL signal is one, or the current limit is active. Should the count be decremented to a lowest possible code (e.g., a code 0), the counter 520 stops any further decrementing. Conversely, combinational logic circuit 515 may increment the count by one bit of its dynamic range if the EA_V.sub.OUT_IN_CTRL signal equals one and one of the following conditions is satisfied: the EA_I.sub.IN_IN_CTRL signal is 0, the EA_V.sub.IN_IN_CTRL signal is 0, or the current limit is not active. When the counter reaches a default level such that I.sub.BAT_ref equals a default value, counter 520 stops any further incrementing. Note that the default level of I.sub.BAT_ref equals one of I.sub.PRE_CHG, I.sub.CHG_TRICKLE, or I.sub.FAST_CHG depending upon the charge profile.

[0038] In some implementations, the amount of incrementing and decrementing based upon which error signal is being selected by PWM modulator 510 to control the duty cycle of switching power converter 105 may be tuned such as through a one-time programmable (OTP) configuration of battery charger 500. Some example operating scenarios for battery charger will now be discussed.

[0039] A first scenario (Scenario 1) is shown in FIG. 6. Scenario 1 occurs when a system load causes a sudden demand in the load current I.sub.SYS while the battery current I.sub.BAT is being regulated to a default level such as I.sub.FAST_CHG. Prior to a time A, PWM modulator 510 was selecting for the output voltage error signal from error amplifier 120 for the duty cycle control so that the output voltage V.sub.SYS is regulated to the minimum system voltage V.sub.SYS_MIN. At time A, the load current I.sub.SYS increases with a relatively high slew rate. This increase in the load current I.sub.SYS causes PWM modulator 510 to stop controlling the duty cycle based upon the output voltage error signal. The output voltage V.sub.SYS thus collapses (droops) to cross the under voltage threshold V.sub.SYS_UNDER_TH at a time B. Comparator 535 then asserts the transient response signal (designated as V.sub.SYS_UNDER), which causes the reset of the count. In addition, the lack of control by the output voltage error signal causes a decrementing of the count, which in turn causes auxiliary battery current error amplifier 135 to throttle (reduce) the battery current I.sub.BAT so that the output voltage V.sub.SYS recovers at a time C to again equal the minimum system voltage V.sub.SYS_MIN. This recovery in the output voltage V.sub.SYS causes pulse width modulator 510 to again use the output voltage error signal to control the duty cycle, which causes the EA_V.sub.OUT_IN_CTRL signal to equal 1. The count then begins to increment until the count causes the battery current I.sub.BAT to exceed the critical value I.sub.BAT_CRIT. The count will then begin to dither up and down at a time D, to cause the battery current I.sub.BAT to dither about the critical value I.sub.BAT_CRIT. At a time E, the load current I.sub.SYS decreases, which causes the EA_V.sub.OUT_IN_CTRL signal to equal one. The count will then continue to increment until the battery current reaches a default level (e.g, I.sub.FAST_CHG). The sudden decrease of the load current I.sub.SYS causes a mild overshoot of the output voltage V.sub.SYS above the minimum system voltage V.sub.SYS_MIN.

[0040] A second scenario (Scenario 2) is shown in FIG. 7. Scenario 2 occurs when the battery current I.sub.BAT changes default levels (e.g., from I.sub.CHG_TRICKLE to I.sub.FAST_CHG) in the presence of a load current I.sub.SYS. Prior to a time A, PWM modulator 510 was selecting for the output voltage error signal from error amplifier 120 for the duty cycle control so that the output voltage V.sub.SYS is regulated to the minimum system voltage V.sub.SYS_MIN. At time A, the battery current I.sub.BAT begins to increase from the I.sub.PRE_CHG level. At a time B, the battery current rises to I.sub.BAT_CRIT. PWM modulator 510 then begins to dither between controlling the duty cycle based upon the battery current error signal or the output voltage error signal. The EA_V.sub.OUT_IN_CTRL signal thus dithers between one and zero after time B. At a time C, the load current I.sub.SYS reduces (a reduction in the system load), which causes the EA_V.sub.OUT_IN_CTRL signal to again equal one. The reduction in the load current I.sub.SYS at time C causes a minor overshoot of the output voltage V.sub.SYS above the minimum system voltage V.sub.SYS_MIN.

[0041] A third scenario (Scenario 3) is shown in FIG. 8. Scenario 3 occurs when the load current I.sub.SYS gradually increases from a lower level I.sub.SYS1 to a higher level I.sub.SYS2 while the battery current I.sub.BAT is regulated to a default level such as to I.sub.FAST_CHG. Prior to a time A, PWM modulator 510 was selecting for the output voltage error signal from error amplifier 120 for the duty cycle control so that the output voltage V.sub.SYS is regulated to the minimum system voltage V.sub.SYS_MIN. The increase in the load current I.sub.SYS begins at time A, which causes the EA_V.sub.OUT_IN_CTRL signal to fall to zero. The count then starts to decrement, which causes the battery current I.sub.BAT to fall below I.sub.BAT_CRIT at a time B, which causes the EA_V.sub.OUT_IN_CTRL signal to begin to be dithered between one and zero. The battery current I.sub.BAT then also dithers about I.sub.BAT_CRIT, until a time C when the load current I.sub.SYS is again increased. This increase in the load current I.sub.SYS causes the EA_V.sub.OUT_IN_CTRL signal to fall to zero. The count is then decremented to the lowest possible code at a time D. Since the load current I.sub.SYS continues to increase after time D and no further throttling of the battery current I.sub.BAT can be produced, the output voltage V.sub.SYS begins to fall, until the V.sub.SYS_UNDER threshold is crossed at a time E.

[0042] Note the advantages of the controlling the battery current I.sub.BAT based upon a current threshold that is increased or decreased based upon whether the duty cycle is being controlled by the output voltage error signal or the input voltage/input current error signals. As discussed with regard to conventional charger 100, it is advantageous to control the conductance of the QBAT transistor 140 based upon a difference between the battery current I.sub.BAT and a threshold current I.sub.BAT_ref because the resulting control of the battery current I.sub.BAT is effectively in series with the control of the output voltage V.sub.SYS. But the output voltage V.sub.SYS is then subjected to unwanted droops below the minimum system voltage V.sub.SYS min such as in the presence of sudden increases in the load current. The shunt feedback discussed with regard to charger 300 can more robustly regulate the output voltage V.sub.SYS in the presence of such load transients but the resulting shunt feedback then has a complicated interaction with the regulation of the output voltage V.sub.SYS that can lead to instabilities. In contrast, charger 500 has an improved output voltage regulation analogous to that provided by a conventional shunt feedback approach but with the stability of the battery current feedback loop being effectively in series with the output voltage feedback loop.

[0043] Those of some skill in this art will by now appreciate that many modifications, substitutions and variations can be made in and to the materials, apparatus, configurations and methods of use of the devices of the present disclosure without departing from the scope thereof. In light of this, the scope of the present disclosure should not be limited to that of the particular embodiments illustrated and described herein, as they are merely by way of some examples thereof, but rather, should be fully commensurate with that of the claims appended hereafter and their functional equivalents.