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BQ25895: BATFET turn off at VBAT_OTG(about 2.85V) in boost mode

Harson
Expert 3700 points
Part Number: BQ25895

Hi, Team

My customer Hytera feedback that when they are using BQ25895, they found a problem doesn't match with datasheet.

If we set BQ25895 in Boost mode, PMID outputs 5V.

Then battery voltage drops eventually, if VBAT gets VBAT_OTG, about 2.85V, BQ25895 will exit boost mode as expected, but it will also turn off Q4, VSYS will lost the power from battery.

If we don't set it in boost mode, it will turn off Q4 until 2.2V which is as expected from datasheet description.

I test it in a BQ25895EVM, it works the same as customer's board.

Meanwhile, I verified this test in a BQ25892EVM, it will not turn off VSYS when VBAT drops <VBAT_OTG.

Can you please kindly help to check if this is a known issue?

What's our solution to solve it?

Any other parts to replace BQ25895?

  • 0
    TI__Guru*** 143940 points

    Harson,

    The 895 was designed to turn off the BATFET if V(BAT) drops below BATLOWV as a redundant over-discharge protection feature. That condition was erroneously omitted from the datasheet.  There is no newer replacement for the bq25895.  The workarounds include using /QON or the register bit to turn the re-eanble the BATFET.  I also suggest using the host to poll the charger's ADC and closely monitor V(BAT) voltage and then notify the user that the battery is almost depleted before shutdown.