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Battery drains when BQ2057 charge completed

Sachin Tiwari
Prodigy 100 points
Other Parts Discussed in Thread: BQ2057

Hello,

I have been regularly using BQ2057WTS and the battery charge seems to work fine.

Very recently I loaded only the charging section to check the charge behavior. After charging was completed, I disconnected VCC (Adaptor) and left the circuit as it is with battery connected.

Next day, I saw that there was a drop on battery voltage which shouldnt happen ideally since VCC is less than VBat, BQ2057 enters into sleep mode and @sleepmode it should take 10UA 

I am using a P Mosfet configuration and the internal diode conducts and provided Vcc to BQ2057. In this case too, BQ should be in sleep mode as VCC < VBat

Note: The voltage dropped from 8.3V to 8.02V (With only BQ2057 circuit connected and no load whatsoever)

  • 0
    TI__Guru**** 166626 points
    When using PFET, the reverse blocking diode needs to be on the BAT side of the PFET not the VCC side. If not, the PFET internal body diode provides a leakage path to the bq2057 input pins. The datasheet is in the process of being updated.
  • 0 in reply to Jeff F
    Prodigy 100 points

    Jeff,

    Was about to reply the same, I did change the reverse blocking diode to BAT side and it worked fine. I will be testing it for a couple of days with more change/discharge cycles.

    Do make sure that the datasheet is updated so that the future new designers on this product will not have same issues.

    Cheers