Brown out on 3.5v?

1

I see brown out messages in the logs like the below every 24 hours. This is from a NBNAN notecard on the latest 8.1.4 firmware in a custom carrier board. Is this an indicator of a faulty card or not enough voltage? Interesting it happens every 24 hours:

Notecard logs

Sun 04:43:43 PM: boot (brown-out & hard reset [17149] G:Gp2W~..ERspsh)
Sat 04:42:31 PM: boot (brown-out & hard reset [17149])

From health file:

file": "_health.qo",
  "body": {
    "text": "boot (brown-out & hard reset [17149] G:Gp2W~..ERspsh)",
    "voltage": 3.5292969
  },
2

@bkauf

I’ve been advised that you should take a look at the power path for VIO. When the modem powers on (using the VMODEM net), if it causes a glitch on the VIO net, then it can cause that to reset. Generally, it’s worth designing strong traces between the battery supply and the buck/boost regulator serving VIO, allowing for a good amount of capacitance on the output of that regulator. This ensures there is stability if there is a slight glitch.

Also, we advise not using an LDO for VIO; use a super low Iq buck/boosts that are typically capable of delivering at least 300 mA.

Thanks,
Alex

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