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BQ28Z610: new PCB can't access battery.

Keith Wilbern
Prodigy 60 points
Part Number: BQ28Z610

I have a motherboard-like PCB with processor,ram, etc. and I integrated the BQ28Z610 to monitor 2 series Li batteries that are attached to the motherboard.  I expected the BQ28Z610 to allow the battery voltage to pass through the NFETs and allow a fresh board to power up.  However, this part blocks the battery voltage and thus the board can't power up to talk to the chip with the I2C bus.  Classic chicken and egg issue.   I had to short around the NFETs to allow the battery voltage to get to my regulators so that I could start debugging the rest of the board.  I have basically finished debugging the board and now want to get the fuel gauge chip to work.  Am I missing something obvious?  It seems like the chip is expecting to be turned on /programmed from the I2C port before it allows battery access, but I have to power up the board before I can use the I2C port.  Is there another part that I should be using instead? 

Thanks,

Keith

  • 0
    TI__Mastermind 42535 points

    Hi Keith,

    The gauge wakes up from shutdown when it sees a PACK voltage (charger connection). Once it sees a PACK voltage, if you have sent a FET_ENABLE command before, the FETs will be closed. You seem to be using the gauge independently from the batteries, that is OK, but in reality this gauge was designed to be integrated with the battery pack and then the smart pack would be connected to the system.

  • 0 in reply to Batt
    Prodigy 60 points

    My system does have pack voltage from the charger, but the fuel gauge chip doesn't allow any current to flow through the NFETs.  I have never written to this part, as it is a brand new built board.  As the datasheet is lacking on the first start up sequence, what should happen when a brand new fuel gauge is connected to the batteries?  Should there not be a pack voltage to simulate the battery pack removed from the unit and then I should connect the charger to provide pack voltage?  I believe I have tried this scenario and the fuel gauge chip doesn't turn on the FETs.  Does this chip assume that your product is powered from some other means and can talk I2C even though the fuel gauge keep the FETs turned off?   For example, if I short around the FETs to allow my unit to turn on, then talk I2C to the fuel gauge to possibly do the SHA authorization, etc.  then will the fuel gauge start working?

    Keith

  • 0 in reply to Keith Wilbern
    TI__Mastermind 42535 points

    Hi Keith,

    You need to provide a pack side voltage to wake the gauge up. If your gauge's FETs have not been enabled, please keep the pack side voltage on until you send the FET enable command. Once your FETs are enabled, the gauge will stay on even if the PACK voltage drops to 0, until either a shutdown command is sent or the battery voltage drops below shutdown voltage.