ZHCSI59I July 2009 – May 2018 TPS65070 , TPS65072 , TPS65073 , TPS650731 , TPS650732
UNLESS OTHERWISE NOTED, this document contains PRODUCTION DATA.
The battery charger is designed to operate with the two NTCs listed above. These will give a cold and hot temperature threshold of 0°C and 45°C. If the charger needs to operate (charge) in a wider temperature range, for example, –5°C to 50°C, the circuit can be modified accordingly. The NTC changes its resistance based on the equation listed below:
With:
R25 = NTC resistance at 25°C
T = temperature in Kelvin
T0 = reference temperature (298K)
Resistor RT2 in parallel to the NTC is used to linearize the resistance change with temperature of the NTC. As the NTC has a high resistance at low temperature, the resulting resistance of NTC in parallel with RT2 is lower especially for low temperatures where the NTC has a high resistance, so RT2 in parallel has a significant impact. For higher temperatures, the resistance of the NTC dropped significantly, so RT2 in parallel does not change the resulting resistance a lot. See Figure 47.