COMP and external reference

RE: COMP and external reference

Stefan Birnir Sverrisson — Fri, 23 Sep 2016 12:36:04 GMT

Good idea! It has been confirmed that there is in fact a hardware bug in COMP peripheral when using external reference in single mode. No workaround reported yet.

RE: COMP and external reference

Thomas R. — Sat, 17 Sep 2016 07:49:45 GMT

Hi Stefan Thanks for the confirmation, for now I will keep using the internal VDD as reference and try to manage the noise with filtering by software.

RE: COMP and external reference

Stefan Birnir Sverrisson — Fri, 16 Sep 2016 13:39:55 GMT

Hi Thomas

I am trying this using the nrf_drv_comp driver. It seems I experience the same things as you, if I set the comparator to external reference, the settings in the TH register do not seem to work. As you said, it seems like the comp is in differential mode. I need to do further verification to see if this is a hardware bug. At this point I see no way around this.

RE: COMP and external reference

Thomas R. — Thu, 15 Sep 2016 11:16:59 GMT

Hi Stefan

I'm using the comp in single ended mode, ISOURCE and is off, the behaviour is the same on both reference input pins. Hysteresis is off, too, the threshold voltage is reconfigured after up events to measure the time needed to charge the capacitor from 24/64Vin up to 40/64Vin and discharge back to 24/64*Vin.

I did some further testing with different input voltages on the reference input. The output is not always zero, but with REFSEL set to 7 the comparator seems to be always in differential mode, regardless of the setting in the MODE register.

RE: COMP and external reference

Stefan Birnir Sverrisson — Tue, 13 Sep 2016 15:44:50 GMT

Hi Thomas

A few questions from my side: Are you using the comp in single or differential mode? What is your hysteresis setting? Do you have ISOURCE enabled? Have you tried both AIN0 and AIN1 for the reference input?