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BQ27750: CFET and DFET

Rahul Kumar92
Intellectual 415 points

Part Number: BQ27750

Hey,

I'm working on BQ27750 single cell unit in my project and facing some following issue:

1. Communicate the BQ27750 with PSOC 4 micro controller via I2C, when Load is connected  DFET and CFET is on after some threshold DFET gets off but still some negative current is shown and battery still get discharge with slow rate. (command is ( 0xAA + 0x3E + 0x20 + 0x00 ) for DFET  & for CFET ( 0xAA + 0x3E + 0x1F + 0x00 )).

2.  On Every reset  the BQ27750 go into the sealed mode. Please tell me the Command of Unseal mode or full access mode and how to write via I2C.

3. On reading Operation_Status Register, it show that BQ27750 is in Reserved mode but I unable to write the register like Shutdown Threshold, Sleep Threshold etc. 

Regards

Rahul Kumar

rahul1.kumar@vnl.in

8860719701

  • 0
    TI__Guru* 76230 points

    Hi Rahul,

    1.if you are able to see some leakage, then you need to debug your board. If the discharge fet is turned off, there shouldn't be a leakage path for discharge current to continue to flow. Can you share your schematic?
    2. Once the gauge is sealed, you can never go back into a permanent unseal state. When you unseal, if a reset command is issued or if there is a POR the gauge will go back to sealed mode. You will need to unseal the gauge to be able to have access to the data flash parameter. You need to send the commands 0x1404,0x3672 one after the other to unseal the gauge. If you use bqstudio, the tool has a once click button that sends both commands one after the other. You can snifff the bus to under stand how to send the commands the way bqstudio does it.
    3. There are still some commands, that are available even if the gauge is sealed. See TRM.
    thanks
    Onyx

  • 0 in reply to Onyx Ahiakwo
    Intellectual 415 points

    I m waiting for your response.

    Regards

    Rahul

  • 0 in reply to Rahul Kumar92
    TI__Guru* 76230 points
    Rahul
    Your schematic for the discharge portion looks ok. You need to check the voltage on the gate of the discharge fet to make sure it is indeed low and not keeping the discharge fet on. Check to ensure the by pass caps across the fets are not shorted. Carry out basic debug of your board to trace where the leakage is coming from.
    thanks
    Onyx