ADC channel resistors

[tomkawal]

I have configured 3 differential ADC channels to sample with timer/PPI/DMA buffer. When I turned everything off, I couldn't get below 20uA current (with only LFCLK running).

I realised recently that resistor dividers, used in SAADC channel config, are not deactivated with SAADC_channel_uninit().

With workaround code below I got current down to 12uA. Obviously, configuring GPIO's didn't didn't help in this case, with ADC channels dividers left on.

//trying to remove any pull_up/pull_down 
channel_0_config.resistor_p = NRF_SAADC_RESISTOR_DISABLED;
channel_0_config.resistor_n = NRF_SAADC_RESISTOR_DISABLED;
channel_1_config.resistor_p = NRF_SAADC_RESISTOR_DISABLED;
channel_1_config.resistor_n = NRF_SAADC_RESISTOR_DISABLED;
channel_2_config.resistor_p = NRF_SAADC_RESISTOR_DISABLED;
channel_2_config.resistor_n = NRF_SAADC_RESISTOR_DISABLED;
nrf_saadc_channel_init(0, &channel_0_config);
nrf_saadc_channel_init(1, &channel_1_config);
nrf_saadc_channel_init(2, &channel_2_config);

Is there any simpler/more elegant code to turn off these resistors, shouldn't that be the part of ..uninit() function?

Regards Tomasz

[Jørgen Holmefjord]

Hi,

The resistors are only connected while the SAADC is sampling, which means that it's not connected for most of the time. The resistors should not be the source of the increased current. This is why it does not make sense to deactivate it in nrf_drv_saadc_channel_uninit function.

Best regards,

Jørgen