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BQ76920: Bq7692003 broke itself After a bit work

Davide Renzetti
Prodigy 215 points
Part Number: BQ76920
Other Parts Discussed in Thread: BQ76200,

Hello,

the problem Is that when I turn on for first time the circuit, It seems to work fine. After some time, the bq7692003 stop working! It happen that the TS1 has a strange voltage: I have a 2.2k resistor beetwen TS1 PIN and 3.3V. I read about 1V on TS1 PIN!

The 3.3V out from regulator of  device Is good, but After some time It goes about 6V! The schematic I adopted Is similar that One on the datasheet. I have 4cells Only with VC4 and VC5 connected togheter. Moreover I note a supply current coming in the regout about 10mA with nothing cooncted on 3.3V PIN output.

When I made these test, I connected the gnd and Bat only, I hadn' t connect the other celle.

Thank you in Advance,

Davide

  • 0
    TI__Guru* 81034 points

    Hi Davide,

    It sounds like the device is indeed being damaged. When you say you connected GND and BAT only - did you connect VC5 and REGSRC as well? Can you send your schematic?

    Thanks,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 215 points

    Thank you Matt,

    yes I also think it is demaged. But I changed it several times!!! It demages after some minutes of working! When I say that I connect GND and Bat only I meant  that for testing, I'm not connecting all the cells, bat only gnd and +12.5V on Vcella4 of scheme. Here there is the scheme:

  • 0 in reply to Davide Renzetti
    TI__Guru* 81034 points

    Hi Davide,

    Thanks for sending the schematic. I see a few things that are different from our typical recommendations, but most of these things should not cause damage to the device. The SRP/SRN pin connections is the thing that might be most likely to cause damage. Normally a sense resistor should be connected between these two pins. If the coulomb counting feature of the device is not used, SRP and SRN should be tied directly to ground.

    If you have not seen this video, it might be helpful to watch: https://training.ti.com/how-create-schematic-bq76920-bq76930-and-bq76940

    The capacitance values used on some of the pins are different from what we use on the EVM and reference designs (CAP1 and REGSRC are usually 1uF). I'm not sure where the V_AFE signal is connected on your schematic - does it connect to something off-page? It would also be good to see the FET portion of the schematic if you are still not able to resolve the issue.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 215 points

    Thank you Matt,

    the sense resistor are in other page and the V_AFE signal doesn' t go to other part of circuit. I can try to change the the CAP1 and REGSCR capacitor, but I don't think they demage the bq7692003! What do you think?

    Regards,

     

  • 0 in reply to Davide Renzetti
    TI__Guru* 81034 points

    Hi Davide,

    I agree - I don't think the capacitor values should cause the damage. However, it might be good to monitor the voltages on these pins during power-up to make sure they get to the correct voltage.

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 215 points
    Hello Matt,
    I assembled in my board, only  the components that you see on scheme that I sent you, without the Bq76200 part. Moreover I assembled the microcontroller for comunicate with Bq76920003. The Bq7692003 is new.
    I supply 12,6V beetwen gnd and Vcella4. I didn't  connect Vcella1, Vcella2, Vcella3. I put 100ohm resistors beetwen Vcella0-Vcella1, Vcella1-Vcella1, Vcella2-Vcella3, Vcella3-Vcella4. I made some measures, I hope they will useful!
    I lifted the REGOUT pin and I meausured the current from REGOUT to 3.3V, it was about 7mA. I lifted the R30 resistor and I measured the current from Vcella4: about 7mA. I put the oscilloscope on pin beetwen R30 and R?:
    I put the oscilloscope on 3.3V:
    It's very strange!!! IT seems that bq7692003 need much current!!!!!!! IT's no possible. When I disassembled the bq7692003, I measured with tester, on the board,  the resistence beetwen REGOUT pin and GND,  beetwen Bat pin and GND and beetwen 3.3Vpin and GND. Always had hundreds kilo ohm.
    Maybe can be the PCB, but I don't know where investigate!
    Regards
  • 0 in reply to Davide Renzetti
    TI__Guru* 81034 points

    Hi Davide,

    This is strange - the BQ76920 should never pull this much current. Is REGOUT supplying power to circuits besides the MCU?

    Matt

  • 0 in reply to Matt Sunna
    TI__Guru* 81034 points

    Hi Davide,

    I haven't heard from you in a while. Have you been able to resolve this issue?

    Thanks,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 215 points

    Hi Matt,

    sincerally, I tried another assembled PCB and I didn't find the same problems. Maybe the problem is on PCB… it's very strange! Iwill update you in the future… sure.

    Thank you again and have a nice day.

    Davide