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BQ77915: Design review

Part Number: BQ77915

Hi Team,

Could you help our customer's concern. 

I have a question regarding the BQ77915 BMS chip. its about a design circuit shown in the documentation.
Under what circumstances would the transistor highlighted in the picture turn on. It seems like the gate and source are tied to 0V.
Also note that from what I read, it seems like VC0 to VC5 are inputs and don't contribute to these balancing transistors turning on and off, but I could be wrong
Best regards,
Jonathan

  • Hey Jonathan,

    The gate bias voltage necessary to turn on the FET connected to Cell 1 is generated by the resistor RINE connected to VC0. Make sure RINE is 1kOhm, and CINE is 0.1uF. The gate should have a threshold voltage less than 1.7V. This is outlined below Figure 9-2 in section 9.3.4 of the datasheet. VC0 does contribute to the balancing transistor being turned on and off. When stacking devices, VC5 will not be used to turn on the transistor for VC6. VC0 of the upper device will do that. Make sure to keep the VC5 of the lower devices and VC0 of the upper devices separate.

    Thanks,
    Caleb