nRF52 Power-fail Comparator expected current consumption

RE: nRF52 Power-fail Comparator expected current consumption

Simonr — Fri, 12 Jun 2020 09:35:51 GMT

Hi again

If your "risky events" don't start/enable the HFCLK already, it should be fine using sd_power_mode_set() to do so as long as you don't mind the additional current consumption. There shouldn't be any other concerns regarding this approach, so feel free to do so, as I can see that you don't have a good way to implement the low power comp.

Best of luck and regards!

Simon

RE: nRF52 Power-fail Comparator expected current consumption

Sydney — Fri, 12 Jun 2020 05:29:14 GMT

After I posted this, I started coming to this realization. I think in all my test scenarios, HFCLK just happened to be running for other reasons, which made it look like the power-fail comparator was generating the warning event even though I thought my board was in idle. For example, one way I tested was by dialing down the voltage on my bench top power supply and verifying via GPIO that the event was being triggered. But I realized that HFCLK was probably enabling periodically for advertisements, which must've been giving the power-fail comparator an opportunity to generate the event. I've since confirmed that a more sudden power loss, like disconnecting power instead of turning the knob, does not generate the power-fail warning event.

Because my potentially-risky high power events are relatively infrequent and short in duration, I can live with the added current required by keeping HFCLK active. So I think I just need a good way to enable HFCLK just before these risky events start and then disable it again after the risky event ends (typically 2-3 seconds later). It looks like I can do this with sd_power_mode_set() to switch between NRF_POWER_MODE_CONSTLAT and NRF_POWER_MODE_LOWPWR as needed. Besides the additional current, are there any concerns with this approach?

I considered using the low power comparator, but I don't have a good external voltage to use as a reference, and the internal references are all proportional to the input voltage, which is what I need to monitor.

Thanks.

RE: nRF52 Power-fail Comparator expected current consumption

Simonr — Thu, 11 Jun 2020 05:58:31 GMT

Even if you call these functions, they still just enable the power-fail comparator and it won't "kick in" until the HFCLK is started by your application. This is mentioned in its electrical specification. See footnote 8 here.

If you'd like to ensure a safe shutdown from IDLE mode when the HF clock is turned off, please check out the Low power comparator instead, as it consumes less power and can be used to compare the input voltage against a reference voltage like the power-fail comparator as well.

Best regards,

Simon