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Schematic review request

Madhuri Akkenepalli
Expert 1215 points
Other Parts Discussed in Thread: BQ78Z100

Greetings ESC,

My customer is working on a new design with the BQ78Z100 and requesting for schematic review. Can you please check the attached schematic and give your feedback?

Thanks.6646.power.pdf

  • 0
    TI__Guru* 76230 points
    Hi Madhuri,
    -Your schematic has some errors.
    -Your discharge fet is flipped. The source and drains are connected wrongly.
    -i do not see connections for your second battery, is this a 1s or a 2s pack?
    - Why do you have your thermistor as DNP? The gauge needs the external thermistor to monitor the temperature of the battery otherwise you will have to use the internal temperature sensor of the gauge. If that is the case, i recommend you have a 10k resistor on the Ts pin instead of leaving it flaoting.
    -Are there pull-ups for your clock and data lines?
    - where does the other end of the sense resistor go to. One end ought to go to the ground of the charger and the other end ought to go to the ground of the gauge.
    -It appears your gauge and charger have the same ground, effectively shorting out your sense resistor. This is wrong. The ground of your charger and that of the gauge ought to be separated. pls refer closely to the reference schematic in the user guide of the device.

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    TI__Prodigy 330 points

    Hi Onyx,

    The customer has the following response (Madhuri is out):

    Can you please relay this back to the engineer that made these comments ?

     

    -Your discharge fet is flipped. The source and drains are connected wrongly.

         You are right , I will fix that.

    -i do not see connections for your second battery, is this a 1s or a 2s pack? 

         This is what I don't get it. It s a 2S battery pack which mean 2 cells in series 7.4V , There is  Power and Groud wires coming out of the battery pack . Can you explain to me what is going on here ? 

     

    - Why do you have your thermistor as DNP? The gauge needs the external thermistor to monitor the temperature of the battery otherwise you will have to use the internal temperature sensor of the gauge. If that is the case, i recommend you have a 10k resistor on the Ts pin instead of leaving it floating.

       I'm not planning to use the NTP pin on this chip because the battery pack has an internal thermistor. I was told by you guys that can just leave it floating and disable it from a register. Your datasheet doesn't mention anything about that. I'll fix that.

     

    -Are there pull-ups for your clock and data lines?

        Yes, there are pull ups on the i2c lines.

     

    - where does the other end of the sense resistor go to. One end ought to go to the ground of the charger and the other end ought to go to the ground of the gauge.
    -It appears your gauge and charger have the same ground, effectively shorting out your sense resistor. The ground of your charger and that of the gauge ought to be separated. please refer closely to the reference schematic in the user guide of the device.

           I'll take a look at these. Also it would be very helpful to mention the refdes .

     

     

  • 0 in reply to Farshad Farahbakhshian
    TI__Guru* 76230 points

    Hi Farshad,

    like i said earlier, pls reference the schematic in the user guide of the EVM. The reference schematic has chggnd and gnd. The chggnd is on the other side of the sense resistor. ie the pack + and Pack- pins. The gauge  IC has to have a different ground so you are not shorting out the sense resistor.

    pls look at the ref schematic on how the battery connectors for the terminals of the battery should be

    thanks

    Onyx