Input protection

RE: Input protection

hmolesworth — Fri, 09 Dec 2022 23:53:28 GMT

Quite so; although of course it might work sometimes then occasionally get locked up. An other alternative is to use a crowbar or a boost converter which guarantees output discharge when disabled.

RE: Input protection

Andrew Mowry — Fri, 09 Dec 2022 23:06:51 GMT

Thank you-- is that the same issue that you mentioned here:?

Protection diodes on NRF52840: clamping current

I'm not sure I totally understand the implications of this, but that other thread you make it sound bad :). Is the issue basically that the MCU won't be able to restart if the power is momentarily interrupted for some reason?

RE: Input protection

hmolesworth — Fri, 09 Dec 2022 22:41:23 GMT

You may find a reset is affected where the pin provides phantom power to the MCU and reset circuit via the schottky clamp diode if power is removed from the MCU after being applied. At low VCC this is tiny, few 10's nA, and so the 10k won't help. No worries if MCU power is not removed and restored by the boost converter being truned on, then off, then sometime later back on. I have experienced this.

I would suggest a test to illustrate this if you have time. The workaround is often to use a buffer/level shifter powered by the MCU VCC.

RE: Input protection

Andrew Mowry — Fri, 09 Dec 2022 21:05:10 GMT

Great, thank you!

RE: Input protection

ketiljo — Thu, 08 Dec 2022 09:20:03 GMT

You can use a 10k series resistor here. This will limit the current in the ESD protection diodes and clamp the voltage to VDD + 0.3 V.