Want to sample ADC input at different ADC reference voltages

[Nilesh Dalvi]

Here i am using the SAADC driver of NRF52840 for my application, using SAADC api's i want to sample the 

adc input at different adc reference voltages as per the project need.

ADC voltage references are 1.45 , 2.5 likewise i want to sample it. As given SAADC default driver configuration.

there are only 2 option for the internal voltage references .

NRF_SAADC_REFERENCE_INTERNAL = SAADC_CH_CONFIG_REFSEL_Internal, ///< Internal reference (0.6 V).
NRF_SAADC_REFERENCE_VDD4 = SAADC_CH_CONFIG_REFSEL_VDD1_4 ///< VDD/4 as reference.

Here i want to get some suggestion from you that how to use it at different ADC ref voltage.

NRF52840 has internal ref range is from - 1.7 to 3.6 VDD.

Thanks,

NIlesh

[ovrebekk]

Hi

How are you generating the 1.45 and 2.5V reference voltages? Are these available as signals on your board?

Can't you just use the internal 0.6V reference, set the ADC gain according to the range of your signal, and perform the required math to calculate what the result would be if a 1.45 or 2.5V reference was used?

Best regards
Torbjørn

[Nilesh Dalvi]

Hello,

After reading the document i just came to know that , i can use the gain setting to get the ADC sample at different voltage references.

i am doing platform code porting here, as in old firmware, they are doing adc sampling of one channel at different ref voltages same think i have to do with NRF52840, but i think i can use the gain settings right?

Thanks

Nilesh

[ovrebekk]

Hi Nilesh

Yes. You can use the gain settings to scale the input voltage so that it is lower than the internal bandgap reference of 0.6V. 

The main important thing is that the input voltage can not be higher than the VDD voltage.

Best regards
Torbjørn