I analyzed it a little more, two different nRF9151 feathers:
(700 mA, short test)
NPM1300 temperature: die 86.35 ° C, gauge 56.99 ° C
NPM1300 gauge voltage 3.48 V
(500 mA, long test)
NPM1300 temperature: die 83.18 °C, gauge 57.33 °C
NPM1300 gauge voltage 3.68 V
(nRF9161 feather, 500 mA, long test)
NPM1300 temperature: die 80.01 °C, gauge 25.00 °C
NPM1300 gauge voltage 3.73 V
My conclusion:
The NTC thermistor of the nRF9151 is close to the NPM1300 and reflects that self-heating.
On charging, it reaches close the 60 °C, so it’s above the default of “WARM” and in danger to get “HOT”.
I’m now not sure, what will be good setup. Future hardware may move the NTC to get not that affected. And for the current hw version I would go to disable the usage of the NTC.
