Highly accurate over current fault protection for battery packs
This disclosure relates generally to the field of providing highly accurate over current fault protection in charging systems and, more particularly, to systems in which the charge over current protection (COCP) and discharge over current protection (DOCP) circuitry in electronic devices are particularly resilient to variations in field-effect transistor (FET) resistance with temperature, gate drive, and/or process shift; variations in printed circuit board (PCB) resistance; and variations in integrated circuit (IC) trip voltages. Through the use of novel circuit designs disclosed herein that effectively “bypass” the traditional “power FETs” that control the current flow to the battery pack(s) of the electronic device using a novel “sense FET” concept, the major sources of error in current sensing may be eliminated without compromising any safety features of the electronic device, thus allowing for more accurate over current fault protection systems for battery packs across a wide range of operating conditions and temperatures.
1. A battery pack comprising:
at least one cell;
a first protector circuit coupled to the at least one cell and configured to monitor a battery pack current;
a first power field-effect transistor (FET) circuit, coupled to and controlled by the first protector circuit and further coupled to the at least one cell, operable to disconnect the at least one cell, thereby interrupting the battery pack current, responsive to an overcurrent condition of the battery pack current; and
a first sense FET circuit, coupled to the first protector circuit and the first power FET circuit, so as to enable the first protector circuit to sense the battery pack current, thereby reducing current measurement errors caused by the first power FET circuit,
wherein the first sense FET circuit is connected in a first direction to a first input of the first protector circuit via a first sense resistor.
2. The battery pack of claim 1 , further comprising:
a second protector circuit comprising two or more inputs connected to the at least one cell to regulate the battery pack current;
a second power FET circuit, coupled to the second protector circuit and controlled by the second protector circuit, and further coupled to the at least one cell, so as to control the battery pack current;
a second sense FET circuit, coupled to the second protector circuit and the second power FET circuit, so as to allow the second protector circuit to sense the battery pack, thereby reducing current measurement errors caused by the second power FET circuit,
wherein the second sense FET circuit is connected in a second direction to a first input of the second protector circuit via a second sense resistor; and
a third resistor connected between a second input of the second protector circuit and the at least one cell.
3. The battery pack of claim 1 , wherein the first sense FET circuit is connected in a third direction to a second input of the first protector circuit.
4. The battery pack of claim 2 , wherein the second sense FET circuit is connected in a fourth direction to a second input of the first protector circuit.
5. The battery pack of claim 3 , wherein the first sense FET circuit is further connected in the third direction to the second input of the first protector circuit via a fourth resistor.
6. The battery pack of claim 4 , wherein the second sense FET circuit is further connected in the fourth direction to the second input ,of the first protector circuit via a fifth resistor.
7. The battery pack of claim 1 , wherein the first power FET circuit and the first sense FET circuit are controlled by one or more of the same signals from the first protector circuit.
8. The battery pack of claim 2 , wherein the second power FET circuit and the second sense FET circuit are controlled by one or more of the same signals from the second protector circuit.
9. The battery pack of claim 1 , wherein the current measurement errors caused by the first power FET circuit comprise one or more of the following: variations in FET resistance with temperature, gate drive, or process shift; variations in printed circuit board (PCB) resistance; and variation in integrated circuit trip voltage.
10. The battery pack of claim 2 , wherein the current measurement errors caused by the second power FET circuit comprise one or more of the following: variations in FET resistance with temperature, gate drive, or process shift; variations in printed circuit board (PCB) resistance; and variation in integrated circuit trip voltage.
11. The battery pack of claim 2 , wherein the third resistor serves to intentionally debias the second input of the second protector circuit.
12. The battery pack of claim 1 , wherein the first protector circuit controls the first power FET circuit by turning off the first power FET circuit if: a sensed battery pack current is over a predetermined threshold value; a short circuit condition is detected; or a detatched charger state is detected.
13. The battery pack of claim 2 , wherein the second protector circuit controls the second power FET circuit by turning off the second power FET circuit if: a sensed battery pack current is over a predetermined threshold value; a short circuit condition is detected; or a detatched charger state is detected.
14. The battery pack of claim 2 , wherein the second protector circuit comprises a Temperature Cutoff Device.
15. A method of charging a battery pack using one or more cells, the method comprising:
connecting a first protector circuit having two or more inputs to the one or more cells;
monitoring, by the first protector circuit, a battery pack current;
controlling, by the first protector circuit, a first power field-effect transistor (FET) circuit coupled to the first protector circuit and the one or more cells, so as to disconnect the one or more cells, responsive to an overcurrent condition of the battery pack current; and
sensing, by a first sense FET circuit coupled to the first protector circuit and the first power FET circuit, the battery pack current, thereby reducing current measurement errors caused by the first power FET circuit,
wherein the first sense FET circuit is connected in a first direction to a first input of the first protector circuit via a first sense resistor.
16. The method of claim 15 , further comprising:
monitoring, by a second protector circuit comprising two or more inputs connected to the one or more cells, a battery pack current;
controlling, by the second protector circuit, a second power FET circuit coupled to the second protector circuit and the one or more cells, so as to disconnect the one or more cells, responsive to an overcurrent condition of the battery pack current; and
sensing, by a second sense FET circuit coupled to the second protector circuit and the second power FET circuit, the battery pack current, thereby reducing current measurement errors caused by the second power FET circuit,
wherein the second sense FET circuit is connected in a second direction to a first input of the second protector circuit via a second sense resistor, and
wherein a third resistor is connected between a second input of the second protector circuit and the one or more cells.
17. The method of claim 15 , wherein the first sense FET circuit is connected in a third direction to a second input of the first protector circuit.
18. The method of claim 16 , wherein the second sense FET circuit is connected in a fourth direction to a second input of the first protector circuit.
19. The method of claim 16 , wherein the current measurement errors caused by either the first power FET circuit or the second power FET circuit comprise one or more of the following: variations in FET resistance with temperature, gate drive, or process shift; variations in printed circuit board (PCB) resistance; and variation in integrated circuit trip voltage.
20. A battery pack comprising:
one or more cells;
a first protector circuit comprising two or more inputs connected to the one or more cells to monitor battery pack current;
a first power field-effect transistor (FET) circuit, coupled to and controlled by the first protector circuit and further coupled to the one or more cells, so as to disconnect the battery pack, thereby interrupting the battery pack current, responsive to an overcurrent condition of the battery pack current;
a first sense FET circuit, coupled to the first protector circuit and the first power FET circuit, so as to allow the first protector circuit to sense the battery pack current, thereby reducing current measurement errors caused by the first power FET circuit;
a second protector circuit comprising two or more inputs connected to the one or more cells and configured to determine at least a charging current for the battery pack and a discharging current for the battery pack;
a second power FET circuit, coupled to the second protector circuit and controlled by the second protector circuit, and further coupled to the plurality of cells, so as to control the at least charging current and the at least discharging current for the battery pack; and
a second sense FET circuit, coupled to the second protector circuit and the second power FET circuit, so as to allow the second protector circuit to sense at least a charging current and a discharging current for the battery pack, while eliminating current measurement errors caused by the second power FET circuit,
wherein the second sense FET circuit is connected in a first direction to a first input of the second protector circuit via a first sense resistor, and
wherein a second resistor is connected between a second input of the second protector circuit and the one or more cells.