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BQ28Z610: Battery charging & gauging circuit

Eduardo Barcellos
Intellectual 420 points
Part Number: BQ28Z610
Other Parts Discussed in Thread: BQ25883,

Hello,

I've finished my battery charging and gauging circuit, and I'd like to ask a few questions about it before I send the board to fabrication.

This is the circuit:

My questions are:

1) At label A: I assume that the I2C pullups should be only at the master's side, on the other side of the N1 connector. However, my concern is that if I leave the I2C pins of both chips open without pullups, noise might send unwanted data to the chips. I assume it can indeed be left open, but I'd like to make sure: Can I remove the I2C pullups (R7 and R6) from this board and leave it only at the master's side?

2) At label B: Those 2 capacitors (C12 and C13) are for ESD protection. However, note that VBAT comes directly from the BQ25883 on the same board (no connectors). I left those 2 capacitors there thinking of protection against possible ESD discharges when removing/placing batteries. But looking at it closely, it's not clear if C12 and C13 will even protect against that at all. Will C12 and C13 offer any ESD protection in this configuration? Should I just remove them?

3) What if the user plugs a cellphone charger at N2 (USB connector) with no D+/D- connection. Will the BQ25883 simply disregard D+/D- after trying communication and begin charging the battery with only the provided VBUS?

Thanks!

Eduardo

 

  • 0
    TI__Genius 10385 points

    Eduardo,

    I can take question #3.

    Without D+/D- present the BQ25883 will detect it as an unknown adaptor and set the input current limit to 500 mA. Once the detection scheme is complete, you can override the setting in the IINDPM register to set a new input current limit.

    Alternatively you can short D+/D- to have the detection report USB DCP and set the input current limit to 3.0A. When USB DCP is determined, the charger will automatically execute the ICO algorithm and set the input current appropriately.

    Best Regards,

    Ricardo

  • 0 in reply to Ricardo
    Intellectual 420 points

    Thanks Ricardo.

    What about the GND2 / GND configuration at the BQ28Z610 at the bottom of the circuit? Does it look right? I checked with the datasheet and it does look right (image below):

    But this is still new to me, so better to be sure. The power ground trace shown on the image is indeed for GND2, and has no connection with GND, right?

    Thanks,

    Eduardo

  • 0 in reply to Eduardo Barcellos
    TI__Guru** 105760 points

    Hello Eduardo,

    The I2C lines are actually pulled to ground internally with a 1Mohm resistor, so even if they are not pulled up they will be tied to ground. You can reference the SBS manual for operation when the lines are low: sbs-forum.org/.../sbdat110.pdf

    If you do not expose any of the connections it wouldn't be necessary to keep the capacitors for ESD.

    Your ground connections look good to me from the schematic. You can also use the EVM user's guide which has a full schematic.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Intellectual 420 points

    Thanks very much for your response Wyatt.

    I did look at the BQ28Z610 Evaluation Module user's guide, and the schematics in there has an BQ294502DRVR before the battery. See below:

    Looking at its datasheet, I see it as only additional protection for each individual cell. So, just to make sure: Can I do fine without that chip?

    Thanks again,

    Eduardo

  • 0 in reply to Eduardo Barcellos
    TI__Mastermind 19195 points

    Hi Eduardo,

    If your application requires the secondary protection you may want to consider. The gauge does have protection integrated already.

    Best regards,