SDK_14.2.2 SAADC example test 3.3V output value not full to 0x3ff

[Roger huang]

Hi Supportor 

I have two board, if I didn't set the gain, which used default of SDK, one board output value is 0x2f5, another output ADC value is 0x266.

I set the gain to 1_4, one board can be test ADC value 0x3ff, but another one must be set to 1_3.

that is to say my software is different to diffferent hardware, how to deal with this question, I want to get a value 0x3ff for 3.3V.

the product can not show a unfull power when it is new.

why different IC need different gain level?

NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(PIN_P) \
{ \
.resistor_p = NRF_SAADC_RESISTOR_DISABLED, \
.resistor_n = NRF_SAADC_RESISTOR_DISABLED, \
.gain = NRF_SAADC_GAIN1_3, \
.reference = NRF_SAADC_REFERENCE_INTERNAL, \
.acq_time = NRF_SAADC_ACQTIME_10US, \
.mode = NRF_SAADC_MODE_SINGLE_ENDED, \
.burst = NRF_SAADC_BURST_DISABLED, \
.pin_p = (nrf_saadc_input_t)(PIN_P), \
.pin_n = NRF_SAADC_INPUT_DISABLED \
}

[haakonsh]

If you're sampling a signal from 0V - 3.3V you will need to use 1/6 gain. The expected output at 10-bit resolution will then be:

(1024/600mv) * (3.3V *  1/6) = ~939 dec or 0x3AB.