Charge-pump biased battery protection circuit

• US 7,626,360 B2
• Filed: 12/12/2006
• Issued: 12/01/2009
• Est. Priority Date: 08/11/2006
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Melanson, John L.
• Primary Examiner(s): Tso; Edward
• Assistant Examiner(s): BOATENG, ALEXIS ASIEDUA
• Application Number:
  US11/609,894
• Publication Number:
  US 20080048618A1
• Time in Patent Office: 1,085 Days
• Field of Search: 320/134, 320/136, 320/137, 320/127, 320/128, 320/140, 320/135
• US Class Current: 320/134
• CPC Class Codes: H02J 7/00302 Overcharge protection
• CPC Class Codes: H02J 7/00308 Overvoltage protection
• CPC Class Codes: H02J 7/0031 using battery or load disconnect circuits H02J9/002 takes precedence
• CPC Class Codes: H03K 17/063 in field-effect transistor switches
• CPC Class Codes: H03K 17/687 the devices being field-effect transistors
• CPC Class Codes: H03K 2217/0018 Special modifications or use of the back gate voltage of a FET

Abstract

A charge-pump biased battery protection circuit provides improved efficiency, reduced power dissipation, and reduced complexity in battery powered circuits. A charge pump is utilized to bias the gate of a single pass transistor such that the voltage between the pass transistor gate and the drain/source terminals of the pass transistor have a magnitude greater than the battery voltage, reducing the voltage drop across the pass transistor. The charge pump may be controlled in conformity with a sensed current through the pass transistor, so that at times of lower current loads, power is conserved. The bulk (body) of the pass transistor can be controlled using a resistor coupling a battery terminal to the bulk and a single switch coupling the bulk to a charger/load connection terminal, permitting a single pass transistor to be used for charging and discharging.

Claims

1. A battery protection circuit for charging a battery from a charger and discharging said battery to a load, said circuit comprising:

a pair of battery terminals for connecting said battery;

an input-output terminal for connecting at least one of said load and said charger;

a pass transistor having a first drain/source connection coupled to a given one of said battery terminals and a second drain/source connection coupled to said input-output terminal;

a charge-pump circuit having an output coupled to a gate of said pass transistor, wherein said charge pump circuit charges said gate of said pass transistor to a gate voltage such that a magnitude of a voltage between said gate of said pass transistor and said first drain/source connection is greater than a magnitude of a voltage across said battery terminals; and

a second charge pump having an output coupled to a body of said pass transistor, for charging said body of said pass transistor to a voltage having a polarity opposite a polarity of said gate voltage with respect to both of said drain/source terminals of said pass transistor.

2. The battery protection circuit of claim 1, further comprising a current-sensing circuit for sensing a magnitude of a current provided to said load, wherein an output of said current-sensing circuit is coupled to a control input of said charge pump, and wherein said charge pump only charges said gate of said pass transistor to cause said magnitude of said gate-to-drain voltage of said pass transistor to exceed said magnitude of said voltage across said battery terminals when said magnitude of said current is greater than a threshold current level.

3. The battery protection circuit of claim 2, wherein said current-sensing circuit comprises a current mirror for mirroring a current through said pass transistor.

4. The battery protection circuit of claim 2, wherein said current-sensing circuit comprises a sense resistor coupled in series with one of said drain/source connections.

5. The battery protection circuit of claim 2, wherein said current-sensing circuit comprises a detector for detecting a level of voltage difference between said first drain/source connection and said second drain/source connection of said pass transistor.

6. The battery protection circuit of claim 1, wherein said pass transistor further comprises a bulk terminal connected to a body of said pass transistor, and wherein said circuit further comprises:

a first resistor coupled between said given battery terminal and said bulk terminal;

a switch coupled between said input-output terminal and said bulk terminal; and

a control circuit coupled to a control input of said switch, wherein said switch is set to a conducting state when a charging current is supplied to said input-output terminal to charge said battery and wherein said switch is set to a non-conducting state when a discharging current is supplied from said battery to said input-output terminal.

7. The battery protection circuit of claim 6, further comprising a capacitor coupled from said bulk terminal to said gate of said pass transistor, whereby changes in a voltage of said bulk terminal due to changes in said voltage at said input-output terminal are reduced.

8. A battery protection circuit for charging a battery from a charger and discharging said battery to a load, said circuit comprising:

a pair of battery terminals for connecting said battery;

an input-output terminal for connecting at least one of said load and said charger;

a pass transistor having a first drain/source connection coupled to a given one of said battery terminals and a second drain/source connection coupled to said input-output terminal;

a first resistor connected between said given battery terminal and a bulk terminal of said pass transistor;

a switch coupled between said input-output terminal and said bulk terminal; and

a control circuit coupled to a control input of said switch, wherein said switch is set to a conducting state when a charging current is supplied to said input-output terminal to charge said battery and wherein said switch is set to a non-conducting state when a discharging current is supplied from said battery to said input-output terminal.

9. The battery protection circuit of claim 8, further comprising a second resistor coupled between said input-output terminal and said bulk terminal in series with said switch.

10. The battery protection circuit of claim 8, further comprising a capacitor coupled from said bulk terminal to a gate of said pass transistor, whereby changes in a voltage of said bulk terminal due to changes in a voltage at said input-output terminal are reduced.

11. A method for protecting a battery when charging said battery from a charger and discharging said battery to a load, said method comprising:

controlling a current passing between said battery and one of said charger and said load using a pass transistor;

charging a gate of said pass transistor to a gate voltage such that a magnitude of a gate-to-drain voltage of said pass transistor is greater than a magnitude of a voltage across said battery; and

charging a body of said pass transistor to a voltage having a polarity opposite a polarity of said gate voltage with respect to both drain/source terminals of said pass transistor.

12. The method of claim 11, further comprising detecting a magnitude of said current, and wherein said charging is performed only when said determining determines that said magnitude of said current is greater than said threshold.

13. The method of claim 11, further comprising:

setting a body voltage of said pass transistor by a circuit having a first resistor coupling said body to said load and a switch coupling said body to said battery; and

opening said switch when said current is passing from said battery to said load.

14. A method for protecting a battery when charging said battery from a charger and discharging said battery to a load, said method comprising:

controlling a current passing between said battery and one of said charger and load using a pass transistor;

setting a body voltage of said pass transistor by a circuit having a first resistor coupling said body to said load and a switch coupling said body to said battery;

opening said switch when said current is passing from said battery to said load; and

limiting a current through said switch with a second resistor coupled in series with said switch.

15. The method of claim 14, further comprising charging a body of said pass transistor to a voltage having a polarity opposite a polarity of said gate voltage with respect to both drain/source terminals of said pass transistor.

16. A battery protection circuit for charging a battery from a charger and discharging said battery to a load, said circuit comprising:

a pair of battery terminals for connecting said battery;

an input-output terminal for connecting at least one of said load and said charger;

a pass transistor having a first drain/source connection coupled to a given one of said battery terminals and a second drain/source connection coupled to said input-output terminal;

a charge-pump circuit having an output coupled to a gate of said pass transistor, wherein said charge pump circuit charges said gate of said pass transistor to a gate voltage such that a magnitude of a voltage between said gate of said pass transistor and said first drain/source connection is greater than a magnitude of a voltage across said battery terminals;

a first resistor connected between said given battery terminal and a bulk terminal of said pass transistor;

a switch coupled between said input-output terminal and said bulk terminal; and

a control circuit coupled to a control input of said switch, wherein said switch is set to a conducting state when a charging current is supplied to said input-output terminal to charge said battery and wherein said switch is set to a non-conducting state when a discharging current is supplied from said battery to said input-output terminal.

17. The battery protection circuit of claim 16, further comprising a second charge pump having an output coupled to a body of said pass transistor, for charging said body of said pass transistor to a voltage having a polarity opposite a polarity of said gate voltage with respect to both of said drain/source terminals of said pass transistor.

18. A method for protecting a battery when charging said battery from a charger and discharging said battery to a load, said method comprising:

controlling a current passing between said battery and one of said charger and said load using a pass transistor;

charging a gate of said pass transistor to a gate voltage such that a magnitude of a gate-to-drain voltage of said pass transistor is greater than a magnitude of a voltage across said battery; and

setting a body voltage of said pass transistor by a circuit having a first resistor coupling said body to said load and a switch coupling said body to said battery; and

opening said switch when said current is passing from said battery to said load.

19. A method for protecting a battery when charging said battery from a charger and discharging said battery to a load, said method comprising:

controlling a current passing between said battery and one of said charger and load using a pass transistor;

setting a body voltage of said pass transistor by a circuit having a first resistor coupling said body to said load and a switch coupling said body to said battery;

opening said switch when said current is passing from said battery to said load; and

charging a body of said pass transistor to a voltage having a polarity opposite a polarity of said gate voltage with respect to both drain/source terminals of said pass transistor.