SMALL HIGHLY ACCURATE BATTERY TEMPERATURE MONITORING CIRCUIT

• US 20150103868A1
• Filed: 10/21/2014
• Published: 04/16/2015
• Est. Priority Date: 09/12/2011
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Vu, Luan Minh, Tse, Thomas Y., Hoang, Tuong
• Granted Patent: US 9,863,817 B2
• Time in Patent Office: Days
• US Class Current: 374/183
• CPC Class Codes: G01K 7/22 the element being a non-linear resistance, e.g. thermistor G01K7/26 takes precedence
• CPC Class Codes: G01R 31/382 Arrangements for monitoring battery or accumulator variables, e.g. SoC
• CPC Class Codes: H01M 10/486 for measuring temperature
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A battery temperature monitoring circuit, which has a cold comparator and a hot comparator, achieves high accuracy in a small cell size by utilizing a cold current optimized for the cold comparator and a cold reference voltage, and a hot current optimized for the hot comparator and a hot reference voltage, along with switching circuitry that provides the cold current to the cold comparator as the battery temperature approaches the cold trip temperature, and the hot current to the hot comparator as the battery temperature approaches the hot trip temperature.

Claims

1. A battery temperature measuring circuit comprising:

a first comparator circuit that generates a first output signal, the first comparator circuit comparing a measured voltage to a first reference voltage when the first output signal has a safe logic state, and changing the safe logic state of the first output signal to an unsafe logic state when the measured voltage exceeds the first reference voltage;

a second comparator circuit that generates a second output signal, the second comparator circuit comparing the measured voltage to a second reference voltage when the second output signal has a safe logic state, and changing the safe logic state of the second output signal to an unsafe logic state when the measured voltage falls below the second reference voltage; and

a current source circuit connected to the first comparator circuit and the second comparator circuit, the current source circuit sourcing a first constant current to the first comparator circuit when the measured voltage rises above an upper voltage, and a second constant current to the second comparator circuit when the measured voltage falls below a lower voltage, the upper voltage being less than the first reference voltage and greater than the second reference voltage, the lower voltage being less than the upper voltage and greater than the second reference voltage.

2. The battery temperature measuring circuit of claim 1 and further comprising a thermistor connected to the first comparator circuit, the second comparator circuit, and the current source circuit.

3. The battery temperature measuring circuit of claim 1 wherein:

the first comparator circuit has a measured input that receives the measured voltage;

the second comparator circuit has a measured input that receives the measured voltage; and

the current source circuit is connected to the measured input of the first comparator circuit and the measured input of the second comparator circuit.

4. The battery temperature measuring circuit of claim 1 wherein the current source circuit includes a third comparator circuit that generates a third output signal, the third comparator circuit comparing the measured voltage to the upper voltage when the third output signal has a first logic state, and changing the first logic state of the third output signal to a second logic state when the measured voltage rises above the upper voltage.

5. The battery temperature measuring circuit of claim 4 wherein the current source circuit sources the first constant current in response to the second logic state of the third output signal, the second logic state of the third output signal indicating that the measured voltage is greater than the upper voltage.

6. The battery temperature measuring circuit of claim 4 wherein the current source circuit further includes:

a first constant current source that sources the first constant current;

a second constant current source that sources the second constant current; and

a switch connected to the first constant current source, the second constant current source, the first comparator circuit, the second comparator circuit, and the third comparator circuit, the switch passing the first constant current when the third output signal has the second logic state, and the second constant current when the third output signal has the first logic state.

7. The battery temperature measuring circuit of claim 6 wherein the switch is a multiplexor.

8. The battery temperature measuring circuit of claim 1 wherein the first comparator circuit has an input offset voltage, and the first constant current has a magnitude that compensates for the input offset voltage of the first comparator circuit.

9. The battery temperature measuring circuit of claim 8 wherein the second comparator circuit:

has an input offset voltage, and the second constant current;

has a magnitude that compensates for the input offset voltage of the second comparator circuit.

10. The battery temperature measuring circuit of claim 4 wherein the first comparator circuit compares the measured voltage to a third reference voltage when the first output signal has the unsafe logic state, and changes the unsafe logic state of the first output signal to the safe logic state when the measured voltage falls below the third reference voltage, the third reference voltage being less than the first reference voltage.

11. The battery temperature measuring circuit of claim 10 wherein the second comparator circuit compares the measured voltage to a fourth reference voltage when the second output signal has the unsafe logic state, and changes the unsafe logic state of the second output signal to the safe logic state when the measured voltage rises above the fourth reference voltage, the fourth reference voltage being greater than the second reference voltage.

12. The battery temperature measuring circuit of claim 11 wherein the third comparator circuit compares the measured voltage to the lower voltage when the third output signal has the second logic state, and changes the second logic state of the third output signal to the first logic state when the measured voltage falls below the lower voltage.

13. The battery temperature measuring circuit of claim 12 wherein the current source circuit sources the second constant current in response to the first logic state of the third output signal, the first logic state of the third output signal indicating that the measured voltage is less than the lower voltage.

14. A method of operating a battery temperature measuring circuit comprising:

outputting a first constant current to a first comparator circuit and a second comparator circuit when a measured voltage exceeds an upper voltage; and

outputting a second constant current to the first comparator circuit and the second comparator circuit when the measured voltage falls below a lower voltage.

15. The method of claim 14 wherein a magnitude of the first constant current compensates for an input offset voltage of the first comparator circuit, and a magnitude of the second constant current compensates for an input offset voltage of the second comparator circuit.

16. The method of claim 14 wherein the first comparator circuit:

generates a first output signal, compares the measured voltage to a first reference voltage when the first output signal has a safe logic state, and changes the safe logic state of the first output signal to an unsafe logic state when the measured voltage exceeds the first reference voltage.

17. The method of claim 16 wherein the second comparator circuit generates a second output signal, compares the measured voltage to a second reference voltage when the second output signal has a safe logic state, and changes the safe logic state of the second output signal to an unsafe logic state when the measured voltage falls below the second reference voltage.

18. The method of claim 17 wherein the upper voltage is less than the first reference voltage and greater than the second reference voltage, and the lower voltage is less than the upper voltage and greater than the second reference voltage.

19. The method of claim 18 wherein the first comparator circuit compares the measured voltage to a third reference voltage when the first output signal has the unsafe logic state, and changes the unsafe logic state of the first output signal to the safe logic state when the measured voltage falls below the third reference voltage, the third reference voltage being less than the first reference voltage.

20. The method of claim 19 wherein the second comparator circuit compares the measured voltage to a fourth reference voltage when the second output signal has the unsafe logic state, and changes the unsafe logic state of the second output signal to the safe logic state when the measured voltage rises above the fourth reference voltage, the fourth reference voltage being greater than the second reference voltage.