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nRF52832: Power OFF/Reset with UART connected

Marco

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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  • 0

    Thank you Ole for your support. Your help together with this link are the answer: devzone.nordicsemi.com/.../ It turned out that my sensor was not resetting according to its specifications. This was happening because the sensor did not get powered off properly (1.57V in due to UART pins). Is there any way I could force the UART pins to "disconnect" so that any voltage on UART won't affect the system?

  • 0 in reply to Marco

    Thank you Ole for the suggestion, however I cannot modify my actual board (just used for prototyping). Could my actual setting (UART Rx/Tx pins held at 3.3V leaking current throughout the nRF chip) cause any HW damages to the nRF itself? For instance, the nRF specification states that Pin in/out voltage should fall in the range -0.3V to Vdd+0.3V=1.87V. But this specification is not met when the main power source is removed. In such case pin connected to UART lines get 3.3V and Vdd happens to be 1.57V, thus (1.57+0.3)V=1.87V < 3.3V! Isn't it causing a dangerous latch-up condition?

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  • 0 in reply to Marco

    Thank you Ole for the suggestion, however I cannot modify my actual board (just used for prototyping). Could my actual setting (UART Rx/Tx pins held at 3.3V leaking current throughout the nRF chip) cause any HW damages to the nRF itself? For instance, the nRF specification states that Pin in/out voltage should fall in the range -0.3V to Vdd+0.3V=1.87V. But this specification is not met when the main power source is removed. In such case pin connected to UART lines get 3.3V and Vdd happens to be 1.57V, thus (1.57+0.3)V=1.87V < 3.3V! Isn't it causing a dangerous latch-up condition?

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