nRF52840 Power-On Reset circuitry

[JordanYates]

Section 18.6.2 of the nRF52832 datasheet (Power-On reset) specifies the following:

---

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.

---

Does the same condition also apply to the nRF52840 chipset?

[Håkon Alseth]

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

[JordanYates]

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.

[Håkon Alseth]

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).

[JordanYates]

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.

[Håkon Alseth]

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?