SAADC read only 3V although input is 3.3V

[Nahan_Trogn]

Hi, I use default config:

#define NRFX_SAADC_DEFAULT_CHANNEL_CONFIG_SE(PIN_P) \
{                                                   \
    .resistor_p = NRF_SAADC_RESISTOR_DISABLED,      \
    .resistor_n = NRF_SAADC_RESISTOR_DISABLED,      \
    .gain       = NRF_SAADC_GAIN1_6,                \
    .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          \
}

And this is may calculation:

    nrfx_saadc_sample_convert(0, &saadc_val);
    temp = 3600 * saadc_val / 1024.0;

The temp is about 3.0V when real input is 3.3V. Pls give me a solution, Tks in advanced

[Håkon Alseth]

Hi,

 

The SAADC input voltage cannot exceed VDD_NRF. What is the VDD_NRF on your board?

 

Kind regards,

Håkon

[Nahan_Trogn]

Hi,

What is VDD_NRF mean? I use nRF52-DK (nrf52832) with usb cabble connect direct to my PC to programe. So the value of VDD_NRF is?

[Håkon Alseth]

Hi,

 

It is approx. 2.9V (3.3V - diode drop) on the DK.

 

Kind regards,

Håkon

[Nahan_Trogn]

Hi,

Tks for your information, I just measure and It is really 2.9V