Measuring VDD in nRF54L15DK

[Narendra]

Hi,

I like to measure the VDD in nRF54L15DK using ADC. 

I have flash the example firmware ..\v3.1.0\zephyr\samples\drivers\adc\adc_dt in my DK.

I can see it is measuring 899mV on channel 2 which has used NRF_SAADC_VDD as ADC input. 

From schematic it looks like nRF54L15 chip VDD set to 1.8V (VDDM_nRF). 

Should it be not 1.8V output?  

I have found below tickets but not much helped,. 

 https://devzone.nordicsemi.com/f/nordic-q-a/121340/measuring-battery-voltage-on-nrf54l15-internal-adc-channel-or-external-circuit-required 

 https://devzone.nordicsemi.com/f/nordic-q-a/116512/how-to-measure-battery-voltage-with-my-custom-nrf54l15-board 

My setup,

• Hardware: nRF54L15DK v0.9.1
• nRF Connect SDK v3.1.0

Regards,

Narendra 

[Narendra]

In example firmware ADC gain set to 1 (ADC_GAIN_1) that's why it is giving 899mv (0.9V) output?

Gain needs to be changed to 2/6, 2/7 or 2/8 to measure correct value?

Setting gain to 2/6 will measure maximum 2.7V VDD input. (0.9/(2/6) = 2.7). 

For 2/7, it will measure up to 3.15V. 

Not able to set 2/8, look like it is not yet supported in SDK. 

Is this correct?

Thanks,

Narendra