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BQ76200: BQ76200 is getting 12V on DSG+CHG EN, but no reaction on CHG and DSG pins

Ran Aloni
Expert 2386 points
Part Number: BQ76200
Other Parts Discussed in Thread: BQ76940, BQ78350-R1

Hi all,

I'm using a BQ76940 + BQ78350-R1 + BQ76200 system.

everything is functioning well except one crucial element.

DSG and CHG fets are open - not passing signal.
BQ76940 is sending 12V signal on both CHG and DSG EN lines - meaning a command to open is being sent.

I can measure ~VBAT on DSG and CHG pins, meaning I have 0 to 0.4V on Vgs of transistors.
in other words - no signal to open the FETs on the other side (typically VBAT + 10V).

the schematics is below - any idea why it doesn't work?
can the chip be malfunctioned?

 

BTW, I can measure 50V on BAT ping and ~58V on VDDCP so it should work.

I can see that PCHG is working properly.

Regards, Ran.

  • 0
    TI__Guru 54715 points

    Hi Ran,
    If the board is built as shown D27 is reversed and will short DSG low. If you look carefully DSG is probably pulsing to the diode voltage pulling down VDDCP and causing CHG to not turn on. I would expect more like 10-11 V between VDDCP and BAT if it is operating properly. To confirm that the part is otherwise OK you might try to disable the DSG FET in the bq78350-R1 controls to see if CHG will come on. Causing a UV condition will likely transition to PCHG mode turning off CHG also, but you could check the VDDCP voltage. Or just remove or turn D27 around and see if it works.

  • 0 in reply to WM5295
    Expert 2386 points

    thanks Willy,

    flipped D27 and it worked perfectly.

    when I just removed it, short circuit ruined the BQ76200 (DSG PIN was not pushing the signal - 0V).

    I took another board and flipped the D27 and it carried the short circuit.

    regards, Ran