# TP4056 - Li-lon Battery Charger temperature problem

I bought an TP4056 component for develop a Li-lon Battery Charger. While I was designing the circuit that was in the datasheet file I realized that the value of two resistors (R1 and R2) was not specified. How do I calculate the value of these resistors?

The datasheet file: TP4056 DATASHEET

The datasheet schematic: ## 2 Answers

The data sheet does have guidance: -

TEMP(Pin 1) :Temperature Sense Input Connecting TEMP pin to NTC thermistor’s output in Lithium ion battery pack. If TEMP pin’s voltage is below 45% or above 80% of supply voltage VIN for more than 0.15S, this means that battery’s temperature is too high or too low, charging is suspended. The temperature sense function can be disabled by grounding the TEMP pin.

So, given that your NTC is defined by the battery (hence you should know its value) you find values for R1 and R2 that tweak the bias point so that at mid-nominal battery temperature, you produce a voltage that is centred between 45% and 80% of the power rail.

• Or work out the NTC's resistance at your chosen temperature limits, derive 2 simultaneous equations giving 45% and 80% of V with those two resistances, and solve for R1 and R2. Its an NTC it'll pull down harder as temp rises, so 45% must correspond to the higher temperature limit. – Brian Drummond Oct 6 '18 at 12:34 Вот реальная схема модуля зарядки. здесь нет R1,R2 [как на схеме в вопросе прим. перев.], pin 1 и 3 на землю и все. Видимо средняя точка созданная R1,R2 нужна для измерения температуры NTC, если его нет, то и нет необходимости в - R1,R2.

translation:
Here's a schematic of an existing charging module. There's no R1, R2 [per diagram in the question] pins 1 and 3 are connected to ground, and that's all. It seems that the node biased by R1, R2 is needed for measuring temperature with NTC, if it isn't present, then there's no need to have R1, R2.