The controller continuously monitors battery temperature by measuring the voltage between the TS pin and AGND. 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 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 MOSFETs. Figure 9-4 summarizes the operation.

Assuming a 103AT NTC thermistor on the battery pack as shown in Figure 9-5, the values of RT1 and RT2 can be determined by using Equation 8 and Equation 9:

Select 0°C to 45°C range for Li-ion or Li-polymer battery,

RTH_COLD = 27.28 kΩ
RTH_HOT = 4.911 kΩ
RT1 = 5.23 kΩ
RT2 = 30.1 kΩ

After select closest standard resistor value, by calculating the thermistor resistance at temperature threshold, the final temperature range can be gotten from thermistor data sheet temperature resistance table.