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POF warning question

John

Hello,

This is a quick question regarding the behavior of the Power Supervisor POF warning. We implemented a fairly naive use of the POF warning where we would log an POF event whenever we received a POF warning. We set the POF warning threshold to 2.7V. After seeing the event when we didn't expect it, we added some debug to log a very recent battery voltage measurement to our log when we logged the POF warning. It showed the battery voltage to be 3.4V.

This led to a number of questions regarding how the POF works. Most of which I could answer based on the reference manual and questions and responses on the forum. However, there were two questions I could not answer.

One, was how long a duration of the voltage below 2.7V is needed to trigger the POF warning. My guess based on what I see in the reference manual is any transient below 2.7V will trigger the warning (assuming of course that the voltage went back above the hysteresis level after each trigger). Is this correct, or does the voltage need to remain below 2.7V for some small amount of time before the warning is triggered?

Two, was is it possible to see false triggers of the POF warning?

Thanks, John

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  • 0

    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.

    1. Do I understand it correctly that you measure 3.4V right before and/or right after the POF warning?
    2. 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?
    3. Is it possible for you to use an oscilloscope to monitor the supply voltage?
    4. 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.
    5. If the problem persists you might consider using LPCOMP instead and see if that helps.
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  • 0

    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.

    1. Do I understand it correctly that you measure 3.4V right before and/or right after the POF warning?
    2. 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?
    3. Is it possible for you to use an oscilloscope to monitor the supply voltage?
    4. 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.
    5. If the problem persists you might consider using LPCOMP instead and see if that helps.
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