RE: Power Supply and Crystal Configuration

Andreas — Mon, 16 Jul 2018 13:35:51 GMT

Hi,

No changes are needed for LDO (non-DC/DC) operation, this is done by default. For 32 kHz you need to modify nrf_clock_lf_cfg_t used when enabling the softdevice. E.g. for SDK 12.3

nrf_clock_lf_cfg_t clock_lf_cfg = NRF_CLOCK_LFCLKSRC;

#define NRF_CLOCK_LFCLKSRC      {.source        = NRF_CLOCK_LF_SRC_RC,            \
                                 .rc_ctiv       = 16,                                \
                                 .rc_temp_ctiv  = 2,                                \
                                 .xtal_accuracy = NRF_CLOCK_LF_XTAL_ACCURACY_20_PPM}

For the 32 MHz crystal you need to update the XTALFREQ register before the oscillator is started by the application, e.g.

// Set the external high frequency clock source to 32 MHz
    NRF_CLOCK->XTALFREQ = 0xFFFFFF00;

The other option is to change the reset value of NRF_CLOCK->XTALFREQ to 32 MHz. Reset value is defined by NRF_UICR->XTALFREQ

Best regards,

Andreas