nRF52840 Power-On Reset circuitry

RE: nRF52840 Power-On Reset circuitry

Håkon Alseth — Fri, 19 Jul 2019 09:14:04 GMT

If you keep the firmware running on the nRF simple, just toggling a pin in main (add a small delay before entering the while-loop), you should be able to see if this is the source of the reset by scoping both VDD_NRF and the toggling gpio.

Do you have a scope picture of the voltage when this transition occurs?

RE: nRF52840 Power-On Reset circuitry

JordanYates — Fri, 19 Jul 2019 09:00:24 GMT

The 600mv is not ripple, it is a transition from 1.8V to 2.4V when an external peripheral is enabled.

We completely understand that this is not desirable behavior, we are just trying to confirm the root cause of the reset so we can be sure to eliminate it in future revisions.

RE: nRF52840 Power-On Reset circuitry

Håkon Alseth — Fri, 19 Jul 2019 08:57:29 GMT

600 mV ripple is very high. What is your VDD nominally?

If a ripple occurs that is so high that the voltage dips below VDD_MIN, you are highly likely to get a full power-on-reset. As a rule of thumb, we recommend that you try to keep ripple low (100 mV or less).

RE: nRF52840 Power-On Reset circuitry

JordanYates — Fri, 19 Jul 2019 08:48:49 GMT

Thanks for the quick reply Håkon,

Is there still some voltage rise that would result in a system reset?

For example 600mV in 100ms

As some additional information, I am seeing a reset on a rise of 600mV (The excessive rise is due to a hardware issue).

No reset reason is stored in RESETREAS, and the reset doesn't occur if the voltage doesn't rise.

I am not sure about the rise time, but it will probably be less than 100ms.

RE: nRF52840 Power-On Reset circuitry

Håkon Alseth — Fri, 19 Jul 2019 08:39:40 GMT

Hi,

This condition does not apply for nRF52840, as the POR has been improved in this device:

https://devzone.nordicsemi.com/f/nordic-q-a/37777/chapter-18-6-1-of-nrf52832-data-sheet-a-step-increase-in-supply-voltage-of-300-mv-or-more-with-rise-time-of-300-ms-or-less-within-the-valid-supply-range-may-result-in-a-system-reset/152807#152807

Kind regards,

Håkon