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BQ28Z610: FET Drive Voltage

Part Number: BQ28Z610

I am struggling to get this chip to output the necessary voltages to drive the CHG and DSG FETs.  I have been playing around with the bq28z610EVM and measuring the voltage at the pins results in a roughly 17.9V output when the FET_EN command is sent to the device.  When working with the BQ chip on our custom hardware, the DSG voltage never gets above 2.5V and the CHG pin seems to always be sitting at 8.2V (which in this case is our input battery voltage).  I've gone through the settings quite a few times and I'm running out of places to look.  Just curious if anyone else has had issues with the FET drive on this part.

  • Hello Alex,

    There's no known problem with the drivers that I am aware of. Your voltage at the CHG pin is sitting at your battery voltage at all times or only when you send the command to turn it on? Could you also share some scope grabs of this occurring if it's when you try to manually set it? 

    I would also double check the connections on the PCB, it seems suspicious that the battery voltage is sitting on that pin. We can review your schematic, this sounds like a hardware issue if it was working on the EVM.

    Sincerely,

    Wyatt Keller

  • Wyatt,

    See the above captures of the CHG and DSG pins.  The first image was taken after booting up the chip (applying VC2 to PACK pin).  The CHG and DSG pins are reported as off through BQ Studio.  The second image is after selecting FET_EN in BQ Studio.  The DSG pin slowly charges up to roughly 2V and the CHG pin slightly increases.  Sending the FET_EN command results in a similar behavior with the signals reducing in amplitude.  The measured battery voltage is 8.35V (VC2=8.35V, VC1 = 4.17V).  

    Below are the captures from the development kit as a reference of what should be happening:

    The dev kit captures are using the same battery voltages.

    I have not probed the board yet to confirm any improper connections to the device yet, but I figured I'd at least provide a little more detail as to what is happening on the pins.

    Thanks,

    Alex

  • Wyatt,

    Did some probing and found that our 10Meg resistors on the gate were populated with Jumpers instead.  Replacing these fixed our issue.  

    No need to look into this any further.  

    Thanks,

    Alex