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nRF52832: Power OFF/Reset with UART connected

Hi,

I wanted to know if the UART pins can cause any issues if kept connected to usb (Rx/Tx pins stable to 3.3V) and directly to the GPIOs of the nRF52, while performing a soft-reset or switching OFF and then ON the device.

I have a sensor (ADXL362) connected to nRF52 via SPI and when I restart the device, all internal registers of this sensor appear to be reset to 0x00 (which should not be possible, they should have some defaults values). Thus this makes me suspect that SPI is not actually succeeding in reading those registers, but no error is shown. When, in addition to switching off the device, I also disconnect the UART connector, then the system gets reset properly and registers of the sensor are read correctly.

Can anyone help me understand what is happening?

Thank you in advance. Marco

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  • If the RX/TX pins are 3.3V while powering off the nRF, the nRF will actually not be powered off because of ESD protection diodes on the pins, see for example this picture. When the voltage on the pin is higher than the Vdd plus the diode forward voltage drop, the diode will start to conduct current and the new Vdd will be the voltage on the input pin minus the forward voltage drop over the diode.

    I don't know why this is messing up your sensor SPI readings. You should connect a logic analyzer to see if the data transferred is correct.

Reply
  • If the RX/TX pins are 3.3V while powering off the nRF, the nRF will actually not be powered off because of ESD protection diodes on the pins, see for example this picture. When the voltage on the pin is higher than the Vdd plus the diode forward voltage drop, the diode will start to conduct current and the new Vdd will be the voltage on the input pin minus the forward voltage drop over the diode.

    I don't know why this is messing up your sensor SPI readings. You should connect a logic analyzer to see if the data transferred is correct.

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