brownout / watchdog reset on voltage drop

[rgrr2]

Hi,

as described here https://devzone.nordicsemi.com/f/nordic-q-a/37056/supervision-timeout-and-unplanned-disconnect our device has a hard current limit of 2mA.

Problem occurs if there is a BLE disconnect due to BLE master getting out of range.  This leads to a retry burst which exceeds the current limit.  To be tolerant against short peaks there is a capacitor bank on the device.  Retry bursts happens until supervision timeout hits (or Vcc drops ;-)).

If these retry bursts last long enough, Vcc begins to drop.

This unfortunately brings the device nRF52832 into an undefined state: watchdog does not occur and even worse, brownout reset also does not do its job.  Not sure, if brownout reset does not occur or if the reset logic does not reset the device to a low power state.  Measurement showed that Vcc is at appr. 1.5V.

Actually only powercycling helps out of this situation which of course is not acceptable.

Any help / suggestion is welcome.

Hardy

[rgrr2]

Ooops... what does that mean?   The system is hold in a reset state until power cycled?  Means that VDD must go down to 0V?  How much current is consumed during this state?

[AmbystomaLabs]

Haakonsh can you please provide a link to the detailed spec describing this aspect of brownout reset? I don't recall reading about it and it does bring up some interesting design challenges.

[haakonsh]

Brown-out reset.

The current consumption is probably equal to the CPU run current. 

The Brown-out detection is a hard limit in any design, you just need to make sure you do not dip below 1.7V and that your dip is not more than 300mV OR you have a slow enough rise time to adhere to:

"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" as per Power-on reset spec.

[mrono]

haakonsh said:

it holds the system in a reset state until power cycled.

So if you ever do get a brown-out event, how do you recover? How is the power cycling going to happen without user intervention?

[haakonsh]

It's designed to require user intervention, like the change of a coin cell battery. 

Do you mind sharing some more information on your power supply and your requirements?