OK to swap +/- on GPIO output on nRF52840 for Neg (-3.3V) PWM Output?

[johnwest]

Hello All,

Maybe someone out there has done this - but is it AOK to swap +/- on the nRF52840 output so a -3.3V PWM signal can be generated?

Are there output zeners on the GPIO's that are going to clamp this?

Thanks In Advance,
johnwest

[ketiljo]

I guess it can be done if you connect VDD of the device to the power supply GND and GND of the device to the -3.3 V supply. You must then let the nRF52840's ground plane be the negative supply. All other peripherals connected to the device must have the same negative ground reference. There's no way to generate a negative output signal if the device have a positive supply. 

[johnwest]

ketiljo,

Hmmm, interesting idea, in theory that should work but not practical obviously.

I was wondering if one or two possibly of the GND pins was assigned to the I/O module where this could be possible but of course the rest of the design would be run at 3.3V levels - and I would imagine there are clamping diodes someplace that may be an issue - but just wanted to ask.

Thanks!
johnwest

[ketiljo]

Min voltage allowed on any GPIO is -0.3 before the clamping diodes starts to conduct. I think you will need some additional circuitry to make this work ;-)