Questions about I/O capability on nRF52832

RE: Questions about I/O capability on nRF52832

ketiljo — Thu, 14 May 2020 10:06:12 GMT

It can't read voltage below ground, but in differential mode, it will show a negative voltage if the input is below the reference.

RE: Questions about I/O capability on nRF52832

Magnus Jonsson — Thu, 14 May 2020 09:50:48 GMT

Thanks for the feedback.

Regarding question 1 above. So the ADC can't read negative voltages in differential mode when V(P) i less than V(N)?

RESULT = [V(P) – V(N) ] * GAIN/REFERENCE * 2(RESOLUTION - m)

If the ADC can't read negative differential voltages . Can we swap the two analog signals in PSELP and PSELN registers instead.

RE: Questions about I/O capability on nRF52832

ketiljo — Thu, 14 May 2020 09:21:59 GMT

1. As long as you are above the -0.3 V minimum voltage on a GPIO, you shouldn't need additional clamping diodes. The ADC will not be able to measure negative voltage though.

2. If you can limit the current that flows into the GPIO to a safe level, < 100 µA, you should be fine. The 0.3 V comes from the voltage drop across the ESD protection dioes. If you have resistor in series with the input, the diodes will in any case limit the voltage to VDD+0.3V. You just need to make sure the current is low enough to avoid damage of the diodes.

3, Small mosfets can be driven directly by the GPIO without a series resistor. The GPIO voltage will drop below the spec if you draw too much current. So in a situation where you are toggling the mosfet gate very fast, the drive capabilites of the GPIO may not be enough to fully charge and discharge the gate capacitor fast enough. A series resistor will just make it worse and lower the usable frequency.