Battery Voltage Reading with a Voltage Divider on the nRF54L15 DK

[AhmedTarek]

Hello Nordic Team,

I am working on measuring battery voltage (3.7V) using a voltage divider (220KΩ and 100KΩ) connected to AIN2 on the nRF54L15 DK.

However, I am experiencing an issue where the ADC reading is incorrect. I am using the existing sample to measure AIN2, but the readings are significantly off (~25mV). Interestingly, when I use an external power supply, the measurements are accurate.

I suspect that the voltage divider circuit or an internal resistor on the AIN2 pin is affecting the readings. Is there any additional configuration required for the GPIO pin to ensure accurate ADC measurements?

Thanks in advance for your support.

Best regards,
Ahmed

[Håkon Alseth]

Hi,

 

Have you tried adding a capacitor, as described in this blog post?

 Measuring Lithium battery voltage with nRF52 

 

Kind regards,

Håkon

[AhmedTarek]

Hi Håkon,

I tried adding a capacitor, but it seems to have no effect.

When I changed the input analog channel to AIN4, I was able to measure the voltage correctly. However, the issue persists with AIN2.

Best regards,
Ahmed

[hmolesworth]

AIN2 is pin P1.06 which on the nRF54L15DK is used as RTS and connects to a DG2788 analogue switch which will load the signal even when nothing is connected to RTS; this is the likely issue.

[Håkon Alseth]

This is a very good catch! I can confirm that this is highly likely the root cause. 

Kind regards,

Håkon