About nPM1300, how to calculated NTC temperature by measured voltage

RE: About nPM1300, how to calculated NTC temperature by measured voltage

Szabolcs — Tue, 16 Dec 2025 09:04:16 GMT

Hi Poki,

yes, there are several pull-up resistors that are selectable by ADCNTCRSEL, but all of them are fixed value resistors, independently of temperature. (as much as fixed-value resistors usually are)
So, if you have a 10K NTC, and select the 10K resistor, your voltage on the pin will be 1.5V*R_NTC/(10K+R_NTC)

RE: About nPM1300, how to calculated NTC temperature by measured voltage

Poki Huang — Tue, 16 Dec 2025 01:55:39 GMT

Hi Szabolcs:

So the pull-up resistor is a fixed value resistor or a variable value resistor?

For our example, the NTC at 25 degrees is 10Kohm, so the pull-up resistor is a fixed 10Kohm resistor for any temperature?

Thank you

Poki

RE: About nPM1300, how to calculated NTC temperature by measured voltage

Szabolcs — Mon, 15 Dec 2025 16:35:27 GMT

Sorry for misunderstanding your question earlier.

Inside the IC, there is a pull-up resistor that pulls the NTC pin to 1.5V internal reference. This is the max range of the ADC. The pullup resistor's value is normally configured to match the NTC resistors 25 degree resistance.

So the ADC measurement value is given by: 1024 * V_NTC / 1.5V.

I your example case, 0.688V results in 1024*0.688/1.5 = 470 over 10 bits, 8 bits of MSBs (0111 0101) in ADCNTCRESULTMSB and 2 bits (10) of LSBs in ADCGP0RESULTLSBS[3:2].

(At 25 degrees, the pull-up and the NTC form a 1:1 voltage divider, so the measured voltage is 0.75V = 512 reg. value).

RE: About nPM1300, how to calculated NTC temperature by measured voltage

Poki Huang — Mon, 15 Dec 2025 02:32:14 GMT

Hi Szabolcs:

I want to know how to mapping NTC measured voltage to it's register

For example our nPM1300 VDDIO supply is 1.8V

So if we measure NTC voltage is 0.688V, it's mapping register value will be (0.688/1.8)*1024=391 or 392 right?

Thank you

Poki

RE: About nPM1300, how to calculated NTC temperature by measured voltage

Szabolcs — Fri, 12 Dec 2025 15:02:26 GMT

Hi Poki,

See the following formula on Page 101 of the nPM1300 Product Specification:

You will also need to set the NTC type properly, ADCNTCRSEL=1 in your case.