Battery pack with a battery protection circuit

1. A circuit comprising:

a monitoring circuit operable for monitoring a cell and generating a monitoring signal indicating a cell voltage of said cell;

a switch coupled in series with said cell;

an integrator circuit coupled to said monitoring circuit and operable for receiving said monitoring signal and a first predetermined threshold and for accumulating a difference between said monitoring signal and said first predetermined threshold over a time period to generate an integrating output; and

a comparator coupled to said integrator circuit and operable for comparing said integrating output to a second predetermined threshold, and for generating a control signal to switch off said switch if said integrating output exceeds said second predetermined threshold.

2. The circuit of claim 1 , wherein said monitoring circuit comprises a selecting circuit operable for selecting said monitoring signal from a plurality of monitoring signals indicating a plurality of cell voltages respectively.

3. The circuit of claim 2 , wherein said monitoring signal indicates the highest cell voltage of said cell voltages, and wherein said first predetermined threshold indicates an over voltage threshold.

4. The circuit of claim 2 , wherein said monitoring signal indicates the lowest cell voltage of said cell voltages, and wherein said first predetermined threshold indicates an under voltage threshold.

5. A battery pack comprising:

a plurality of cells;

a switch coupled in series with said cells; and

a battery protection circuit coupled to said cells and operable for accumulating a difference between a first signal indicating a cell voltage and a predetermined over voltage threshold over a time period to generate an integrating output and for generating a control signal according to a comparison of said integrating output and a second predetermined threshold,

wherein said switch is switched off in response to said control signal to protect said battery pack from an over voltage transient condition if said integrating output exceeds said second predetermined threshold.

6. The battery pack of claim 5 , wherein said battery protection circuit comprises a comparator operable for generating said control signal according to said comparison of said integrating output and said second predetermined threshold.

7. A method comprising:

monitoring a plurality of cell voltages of a plurality of battery cells;

accumulating a difference between a monitoring signal indicating a cell voltage and a first predetermined threshold over a time period for generating an integrating output;

generating a control signal according to a comparison of said integrating output and a second predetermined threshold; and

switching off a switch in series with said battery cells in response to said control signal if said integrating output exceeds said second predetermined threshold.

8. The method of claim 7 , further comprising:

selecting said monitoring signal from a plurality of monitoring signals indicating said cell voltages respectively.

9. The method of claim 7 , wherein said monitoring signal indicates the highest cell voltage of said cell voltages, and wherein said first predetermined threshold indicates an over voltage threshold.

10. The method of claim 7 , wherein said monitoring signal indicates the lowest voltage of said cell voltages, and wherein said first predetermined threshold indicates an under voltage threshold.

11. The battery pack of claim 5 , wherein said battery protection circuit comprises an integrator circuit operable for accumulating said difference between said first signal and said predetermined over voltage threshold over said time period to generate said integrating output.

12. The battery pack of claim 5 , wherein said battery protection circuit is further operable for selecting said first signal from a plurality of signals indicating a plurality of cell voltages of said cells respectively.

13. The battery pack of claim 12 , wherein said first signal indicates the highest cell voltage of said cell voltages.

14. The battery pack of claim 5 , wherein charging of said battery pack is terminated if said switch is switched off.

15. A method for protecting a battery, said method comprising:

monitoring a cell voltage of a cell in said battery;

comparing said cell voltage to a first predetermined threshold and a second predetermined threshold;

comparing a first time duration when said cell voltage exceeds said first predetermined threshold to a first predetermined time period if said cell voltage exceeds said first predetermined threshold;

detecting a first undesired condition if said first time duration exceeds said first predetermined time period;

comparing a second time duration when said cell voltage exceeds said second predetermined threshold to a second predetermined time period if said cell voltage exceeds said second predetermined threshold;

detecting a second undesired condition if said second time duration exceeds said second predetermined time period,

wherein said first predetermined threshold is greater than said second predetermined threshold, and wherein said first predetermined time period is less than said second predetermined time period.

16. The method of claim 15 , wherein a product of said first predetermined threshold and said first predetermined time period is equal to a product of said second predetermined threshold and said second predetermined time period.

17. The method of claim 15 , further comprising:

terminating charging of said battery if said first undesired condition is detected; and

terminating charging of said battery if said second undesired condition is detected.

18. The method of claim 15 , wherein said first predetermined threshold represents a first over voltage threshold, and wherein said second predetermined threshold represents a second over voltage threshold.

19. A battery pack comprising:

a plurality of cells;

a switch coupled in series with said cells; and

a battery protection circuit coupled to said cells and operable for accumulating a difference between a first signal indicating a cell voltage and a predetermined under voltage threshold over a time period to generate an integrating output and for generating a control signal according to a comparison of said integrating output and a second predetermined threshold,

wherein said switch is switched off in response to said control signal to protect said battery pack from an under voltage transient condition if said integrating output exceeds said second predetermined threshold.

20. The battery pack of claim 19 , wherein said battery protection circuit comprises an integrator circuit operable for accumulating said difference between said first signal and said predetermined under voltage threshold over said time period to generate said integrating output.

21. The battery pack of claim 19 , wherein said battery protection circuit comprises a comparator operable for generating said control signal according to said comparison of said integrating output and said second predetermined threshold.

22. The battery pack of claim 19 , wherein said battery protection circuit is further operable for selecting said first signal from a plurality of signals indicating a plurality of cell voltages of said cells respectively.

23. The battery pack of claim 22 , wherein said first signal indicates the lowest cell voltage of said cell voltages.