9.3.18 Temperature Qualification

The controller continuously monitors battery temperature by measuring the voltage between the TS pin and GND. A negative temperature coefficient thermistor (NTC) and an external voltage divider typically develop this voltage. The controller compares this voltage against its internal thresholds to determine if charging is allowed. To initiate a charge cycle, the battery temperature must be within the V_LTF to V_HTF thresholds. If battery temperature is outside of this range, the controller suspends charge and the safety timer, and waits until the battery temperature is within the V_LTF to V_HTF range. During the charge cycle, the battery temperature must be within the V_LTF to V_TCO thresholds. If battery temperature is outside of this range, the controller suspends charge and waits until the battery temperature is within the V_LTF to V_HTF range. The controller suspends charge by turning off the PWM charge FETs. Figure 15 summarizes the operation.

Figure 15. TS Pin, Thermistor Sense Thresholds

Assuming a 103AT NTC thermistor on the battery pack as shown in Figure 20, the value RT1 and RT2 can be determined by using the following equations:

Equation 8.

Equation 9.

For example, 103AT NTC thermistors are used to monitor the battery pack temperature. Select T_COLD = 0ºC and T_{CUT_OFF} = 45ºC; then we get R_T2 = 430 kΩ, R_T1 = 9.31 kΩ. A small RC filter is suggested to use for system-level ESD protection.

Figure 16. TS Resistor Network