Methods and apparatus for measuring battery characteristics
Various embodiments of the present technology may comprise a method and apparatus for measuring battery characteristics. In various embodiments, the apparatus comprises a lithium ion battery and a fuel gauge to monitor the resistance of the battery and the capacity of battery as it ages. The fuel gauge may perform two different methods for computing two different capacity values. The fuel gauge may utilize the capacity values from each method to determine the resistance of the battery as it ages and related battery characteristics, such as the state of health of the battery.
1. An apparatus for determining a state of health of a battery, comprising:
a fuel gauge circuit, coupled to the battery, and configured to:
compute a first battery capacity according to a change in an output voltage of the battery;
compute a second battery capacity according to a voltage across a current shunt coupled to a negative terminal of the battery;
compute a capacity ratio according to the computed first and second battery capacities;
compute an aged resistance value according to the computed capacity ratio;
utilize battery characteristic data to determine an aged capacity according to the computed aged resistance value; and
compute the state of health according to the computed aged capacity and the computed second battery capacity.
2. The apparatus according to claim 1 , wherein the battery characteristic data describes a correlation between a battery resistance and a battery capacity as the battery ages.
3. The apparatus according to claim 1 , wherein:
the fuel gauge circuit comprises a first circuit coupled to a positive terminal of the battery and configured to compute the first battery capacity; and
the first circuit converts the change in the output voltage to a current and integrates the current over a period of time.
4. The apparatus according to claim 3 , wherein:
the fuel gauge circuit further comprises a second circuit coupled to the negative terminal of the battery; and
the second circuit converts the voltage across the current shunt to a current and integrates the current over a period of time.
5. The apparatus according to claim 4 , wherein:
fuel gauge circuit further comprises a logic unit coupled to the first circuit and the second circuit; and
the logic unit computes the capacity ratio by dividing the first battery capacity by the second battery capacity.
6. The apparatus according to claim 4 , wherein:
the fuel gauge circuit further comprises a logic unit coupled to the first circuit and the second circuit; and
the logic unit computes the aged resistance by multiplying an original resistance by the capacity ratio.
7. The apparatus according to claim 4 , wherein:
the fuel gauge circuit further comprises a logic unit coupled to the first circuit and the second circuit; and
the logic unit computes the state of health by dividing the aged capacity by the second battery capacity.
8. A method for determining a state of health of a battery, comprising:
computing a first battery capacity based on the change in an output voltage of the battery;
computing a second battery capacity based on a voltage across a current shunt;
computing a capacity ratio based on the computed first battery capacity and the computed second battery capacity;
computing an aged resistance value based on an original resistance value and the computed capacity ratio;
utilizing capacity-resistance data of the battery to determine an aged capacity according to the computed aged resistance; and
computing the state of health based on the computed aged capacity and the computed second battery capacity.
9. The method for determining a state of health of a battery according to claim 8 , wherein computing a first battery capacity comprises:
converting the change in the output voltage to a current; and
integrating the current over a period of time.
10. The method for determining a state of health of a battery according to claim 8 , wherein computing the second battery capacity comprises:
converting the voltage across the current shunt to a current; and
integrating the current over a period of time.
11. The method for determining a state of health of a battery according to claim 8 , wherein computing an aged resistance value comprises multiplying the capacity ratio by the original resistance value.
12. The method for determining a state of health of a battery according to claim 8 , wherein computing a capacity ratio comprises dividing the first battery capacity by the second battery capacity.
13. The method for determining a state of health of a battery according to claim 8 , wherein computing the state of health comprises dividing the aged capacity by the second battery capacity.
14. A system capable of monitoring a battery and battery characteristics, comprising:
a fuel gauge circuit coupled to the battery, comprising:
a first circuit coupled to the battery, and configured to compute a first battery capacity according to an output voltage of the battery;
a second circuit coupled to the battery, and configured to compute a second battery capacity according to a voltage across a current shunt; and
a logic unit coupled to the first circuit and the second circuit, and configured to:
compute a capacity ratio according to the first and second battery capacities;
compute an aged resistance value according to the computed capacity ratio;
utilize battery characteristic data to determine an aged capacity according to the computed aged resistance value; and
compute the state of health according to the computed aged capacity and the computed second battery capacity; and
an application processor coupled to the fuel gauge circuit and configured to provide an indicator reflecting the state of health of the battery.
15. The system according to claim 14 , wherein the first circuit is coupled to a positive terminal of the battery and converts the change in the output voltage to a current and integrates the current over a period of time.
16. The system according to claim 14 , wherein:
the second circuit converts the voltage across the current shunt to a current and integrates the current over a period of time; and
the current shunt is coupled to the negative terminal of the battery.
17. The system according to claim 14 , wherein the logic unit computes the capacity ratio by dividing the first battery capacity by the second battery capacity.
18. The system according to claim 14 , wherein the logic unit computes the aged resistance by multiplying an original resistance by the capacity ratio.
19. The system according to claim 14 , wherein the logic unit computes the state of health by dividing the aged capacity by the second battery capacity.
20. The system according to claim 14 , wherein the battery characteristic data describes a correlation between a battery resistance and a battery capacity as the battery ages.