UnderVoltage shutdown fail

[edmondhung]

Hi Communities,

I have a custom board build on i.MX6D and PF0100F0A PMIC which powered by a 1-cell Li-po battery.

When the battery voltage is at ~3.1V open, the boot up sequence will make it drop to ~2V then stay at 2.7V.

From the datasheet, this should trigger the PMIC undervolt detect and put it into coincell mode.

But on our board, this fail to happen. The board just shutdown and bootup again and again until the battery protect circuit completely cut the power.

I have tried to pull the PWRON pin to 3V by external power supply, supply the VSNVS by external supply but nothing change.

I just want the undervoltage detection works, shut the system down and stay power off until the battery is about 3.1V which is datasheet stated rising threshold of UVDET and someone press the power button again.

[igorpadykov]

Hi Edmond

seems this is copy from sabre spf-27392 p.19 schematic

when processor powered off, voltage between G2-S2 is equal so

p-fet nonconductive and PWRON should be = 0, pulled down by R571.

On your circuit this is C398. When G2 goes to ground p-fet conducts

and PMIC_ON_REQ (high) goes to PWRON, turning on PMIC.

When PWRON=0 input voltage will not turn on PMIC with

configuration PWRON_CFG=0.

Best regards
igor
-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

[edmondhung]

Hi igor,

Thanks for your help.

Should I replace my C398 to 200k pull-down as sabre schematic?

I have tried this but no help.

[igorpadykov]

I believe yes.

Seems it is necessary to attach permanent licell to VDD_SNVS_IN,

then check signals with oscillosope.

Best regards
igor

[edmondhung]

I have tried your solution:

1. Apply 3VDC as licell to PMIC

2. Change the C398 to 200k pull down

But no help. Exactly same situation as before.

Is there anywhere you think it's suspicious?

Regards,

Edmond

[igorpadykov]

so what is voltage between G2-S2  ?

~igor

[edmondhung]

Thanks for the reply.

measured as below.

Tried remove D17 pin 1, which isolate the un-initialize GPIO from CPU, but no help.

[igorpadykov]

you should try to find why G2=0, it should be the same

as S2. If removing D17 does not help, then you used wrong fet

or there are some layout errors, like short circuits.