POF warning question

RE: POF warning question

MartinBL — Tue, 19 Sep 2017 06:52:40 GMT

4: It might not be mentioned explicitly anywhere. It is one of those "better safe than sorry"-scenarios. It is generally recommended to shut down your peripherals when not in use.

RE: POF warning question

John — Mon, 18 Sep 2017 19:34:06 GMT

I think I have what I need here so I am marking the question answered and closed. Thanks!

RE: POF warning question

John — Mon, 18 Sep 2017 14:17:35 GMT

Also note, we are making an addtional change to our implementation. We are adding a battery measurement to the event handler rather than using the last measurement made. We are also looking at checking the battery voltage via a timer some short time after the event before taking any action to shut down gracefully. 2.7V actually provides us with quite a bit of margin unless we have something like a short on the board.

RE: POF warning question

John — Mon, 18 Sep 2017 13:48:43 GMT

A1: That's what I thought since brownout looks to be controlled by the same logic.

A2:

1: With the data we have the 3.4V was measured within a minute of the event. Not close enough, but it is doubtful the battery truly discharged below 2.7. A transient dip seems much more likely.

2: Absolutely IMHO. I'm an embedded FW guy, but that seems very likely. We'll see what the HW guys say.

3: We have a meeting in an hour or so. I strongly suspect a HW guy will get that action in the meeting

4: That's good to know. Nothing I read before suggested this.

5: Thanks for the suggestion. Plus the LPCOMP uses less power which is always a plus for us.

RE: POF warning question

MartinBL — Mon, 18 Sep 2017 12:48:36 GMT

Q1. You just need a little dip below the threshold to trigger warning.

Q2. I haven't been able to find reports of false triggers like this.

Do I understand it correctly that you measure 3.4V right before and/or right after the POF warning?
Is it possible that current spikes caused by e.g. the radio turning on or by other circuitry on your device cause a voltage drop low enough to trigger the warning?
Is it possible for you to use an oscilloscope to monitor the supply voltage?
It is advisable to disable/enable the POF right before/after your device goes to sleep. It needs HFCLK to run and it is safer to gracefully turn it off while it is not in use.
If the problem persists you might consider using LPCOMP instead and see if that helps.