Combined LDO regulator and battery charger

• US 7,459,886 B1
• Filed: 05/21/2004
• Issued: 12/02/2008
• Est. Priority Date: 05/21/2004
• Status: Active Grant

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Potanina, Elena, Potanin, Vladislav
• Primary Examiner(s): Laxton; Gary L
• Assistant Examiner(s): Fantu; Yalkew
• Application Number:
  US10/850,943
• Time in Patent Office: 1,656 Days
• Field of Search: 320/135, 324/416, 324/413, 323/371, 439/894
• US Class Current: 320/135
• CPC Class Codes: H02J 7/0068 Battery or charger load switching, e.g. concurrent charging and load supply H02J7/0013 takes precedence

Abstract

A method and circuit for simultaneously charging a battery and providing supply voltage to a load. The circuit includes a low-drop-out voltage (LDO) regulator and a constant-current, constant-voltage (CC-CV) regulator. In one embodiment, CC-CV regulator provides a control voltage to the LDO regulator generated by a voltage-controlled current source. As charge voltage approaches battery termination voltage, the control voltage is reduced regulating LDO regulator output to provide constant voltage while decreasing charge current to the battery. In another embodiment, a slow response amplifier and a current mirror in the CC-CV regulator provide a smooth and stable charging current to the battery that is decreased as battery charge approaches a full charge level, while maintaining constant supply voltage to the load. In a further embodiment, an externally programmable amplifier in the CC-CV regulator may enable use of the circuit with varying power sources.

Claims

1. A circuit for charging a battery and providing a supply voltage to a load, comprising:

a voltage regulator that is arranged to receive an input power signal from a power source, a feedback signal, and a control signal, wherein the voltage regulator is further arranged to provide a regulated output signal to the load in response to the feedback signal and in response to the control signal, wherein the feedback signal is based, at least in part, on the regulated output signal; and

a constant current, constant voltage (CC-CV) current regulator that is arranged to provide a charging signal to the battery, and to provide the control signal to the voltage regulator such that a current of the charging signal is maintained at a substantially constant value during a constant current mode and is reduced in response to a battery charge status during a constant voltage mode, wherein the voltage regulator and the CC-CV current regulator are arranged such that the regulated output signal and the charging signal to the battery are simultaneously provided during the constant current mode, wherein the regulated output signal and the charging signal are separate signals, and wherein the voltage regulator is arranged such that the a voltage of the regulated output signal is maintained at a substantially constant value independent of the value of the current of the charging signal.

2. The circuit of claim 1, wherein the voltage regulator is a low-drop-out (LDO) regulator, comprising:

a power pass device that is arranged to provide the regulated output signal from the input power signal; and

an LDO control loop that is arranged to control the power pass device in response to the regulated output signal and in response to the control signal.

3. The circuit of claim 2, wherein the power pass device comprises a power transistor, and wherein the LDO control loop comprises an amplifier and a first voltage divider.

4. The circuit of claim 1, wherein the CC-CV current regulator comprises:

a current sense device that is arranged to sense the current of the charging signal;

a voltage sense integrator that is arranged to provide a first voltage in response to a voltage of the charging signal and the sensed current of the charging signal; and

a current source that is arranged to control the current of the charging signal in response to the first voltage.

5. The circuit of claim 4, wherein the CC-CV current regulator further comprises a second voltage divider that is arranged to provide the control signal to the voltage regulator in response to a combination of a portion of the voltage of the charging signal and a signal that is based on the current of the charging signal.

6. The circuit of claim 5, wherein a ratio of a first resistor and a second resistor of a first voltage divider is substantially equal to a ratio of a first resistor and a second resistor of the second voltage divider.

7. The circuit of claim 4, wherein the current sense device further comprises a current sense resistor, and wherein the current source further comprises a voltage-controlled current source.

8. The circuit of claim 7, wherein an output of the voltage-controlled current source is determined based, in part, on a temperature dependent coefficient.

9. The circuit of claim 4, wherein the current source further comprises a voltage-controlled current source, a current mirror and a transistor, and wherein the voltage sense integrator further comprises a slow-response, transconductance amplifier and a third voltage divider.

10. The circuit of claim 9, wherein a ratio of a first resistor and a second resistor of a first voltage divider of the LDO control loop is substantially equal to a ratio of a first resistor and a sum of a second resistor and a third resistor of the third voltage divider.

11. The circuit of claim 7, wherein the voltage controlled current source is externally programmable for adjustment of the current of the charging signal.

12. The circuit of claim 9, further comprising a capacitor coupled between an output of the slow-response, transconductance amplifier and a ground node for charging current smoothness and stability.

13. The circuit of claim 9, wherein a predetermined reference voltage is coupled to an input of the slow-response, transconductance amplifier.

14. The circuit of claim 1, wherein the power source comprises at least one of a AC/DC adapter, a DC/DC adapter, a Power-over-Ethernet source, and a USB port.

15. The circuit of claim 1, wherein the load comprises at least one of a cellular phone, a personal digital assistant, a laptop computer, and a handheld data collection device.

16. A circuit for charging a battery and providing a supply voltage to a load, comprising:

a low-drop-out (LDO) regulator that is arranged to couple to a power source, the LDO regulator comprising;

a power pass device that is coupled to the power source and the load; and

an LDO control loop that is coupled to the power pass device; and

a constant current, constant voltage (CC-CV) current regulator that is coupled to the LDO regulator, the CC-CV current regulator comprising;

a current sense device that is coupled to the power pass device of the LDO regulator;

a voltage sense integrator that is coupled to the battery and the current sense device; and

a current source that is coupled to the voltage sense integrator and the LDO control loop of the LDO regulator, wherein the LDO voltage regulator and the CC-CV current regulator are arranged such that the supply voltage to the load and a charging current to the battery are simultaneously provided during a constant current mode, and wherein the supply voltage to the load and the charging current to the battery are provided on separate signals.

17. The circuit of claim 16, wherein the CC-CV current regulator is arranged to reduce the charging current to the battery based, in part, on a charging status of the battery, and wherein the LDO regulator is arranged to maintain the supply voltage substantially constant.

18. A constant current, constant voltage (CC-CV) current regulator, comprising:

a current sense device that is arranged to sense a load current;

a voltage sense integrator that is arranged to provide a first voltage in response to a battery charge voltage and the sensed load current;

a current source that is arranged to provide a battery charging current to a battery in response to the first voltage; and

a voltage divider that is arranged provide a control voltage to at least an input node of a voltage regulator in response to a combination of a portion of the battery charge voltage and a voltage to the load that is based, in part, on the battery charging current, wherein the voltage divider comprises a resistor that couples the input node of the voltage regulator to the battery, wherein the CC-CV current regulator is arranged such that the charging current to the battery, during the constant current mode, can be provided while the voltage regulator is providing a regulated voltage to the load.

19. The circuit of claim 18, wherein the current sense device comprises a current sense resistor, and wherein the current source further comprises a voltage-controlled current source.

20. The circuit of claim 18, wherein the current source comprises a voltage-controlled current source, a current mirror and a transistor, and wherein the voltage sense integrator comprises a slow-response, transconductance amplifier.

21. The circuit of claim 18, wherein the CC-CV current regulator is arranged to reduce the battery charging-current based, in part, on a charging status of the battery.

22. A method for charging a battery and providing a supply voltage to a load, comprising:

receiving an input signal from a power source;

providing a regulated output signal to the load and a regulated charging signal to the battery, wherein the regulated output signal and the regulated charging signal are simultaneously provided during a constant current mode;

providing a control signal based, at least in part, on the regulated output signal and the control signal, wherein the control signal is determined by;

providing a first signal based on sensing a current of the regulated output signal;

providing a second signal based on sensing a voltage of the regulated charging signal; and

combining the first signal and the second signal; and

controlling the regulated signal based on the control signal and based on a separate feedback signal wherein the feedback signal is based at least in part on the regulated signal.

23. The method of claim 22, further comprising:

providing a current of the regulated charging signal at a substantially constant value during a constant current mode;

reducing the current of the regulated charging signal based on a battery charging status and maintaining a voltage of the regulated output signal at a substantially constant value during a constant voltage mode; and

maintaining the current of the regulated output signal at a substantially constant value during the constant current mode and during the constant voltage mode.

24. A circuit for charging a battery and providing a supply voltage to a load, comprising:

a means for regulating an input power signal to provide a regulated output signal to a load;

a means for providing a charging signal to a battery;

a means for sensing a current of the regulated output signal;

a means for amplifying the sensed current of the regulated output signal to provide a first control voltage;

a means for sensing a voltage of the charging signal;

a means for amplifying the sensed voltage of the charging signal to provide a second control voltage;

a means for combining the first control voltage and the second control voltage to provide a third control voltage;

a means for controlling the regulated output signal based, in part, on the third control voltage and a separate feedback signal, wherein the feedback signal is based, at least in part, on the regulated output signal; and

a means for reducing the current of the charging signal based, in part, on a charging status of the battery, wherein the means for regulating the input power signal and the means for providing the charging signal are arranged such that the regulated output signal and the charging signal are simultaneously provided during a constant current mode, and wherein the regulated output signal and the charging signal are separate signals.