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BQ77915EVM-014: I can't get it to work properly

Part Number: BQ77915EVM-014
Other Parts Discussed in Thread: BQ77915

Hi, I have the Evaluation Board to check the BQ77915.

I´m interested in the develop one BMS to 3 cells (LiFePo4), but with this evaluation board (first check the evaluation board and next desing a PCB with the part BQ77915), when one of the cells voltage above 3.8V i cant see tha balancing (LED dont turn on). The BMS continues working until the voltage of this cells arrives to 4.2V, then the BMS turns off, until, it has a discharge.

I dont know if i´m doing something wrong or not.

I have to say that I configure the evaluation board to 3 cells. The power supply voltage is around to 20V and the charge current 30mA (the BQ77915 internal dicharge current limit is 50mA, perfect for me, to make the balancing well).

Could you help me, please?

Thanks and regards.

  • Sorry, the discharge current could be maximum 1A.

  • Hi Xabier,

    Unfortunately, our engineering team is unavailable for the rest of the week due to holidays. We will get back to you by the 29th of December next week.

  • Hello Xabier,

    Did you place the shunt at J5 to enable cell balancing? CBI must be shorted to GND to enable cell balancing. Cell balancing doesn't automatically start at 3.8-V, it starts once a cell reaches this voltage and there is a cell below Vstart (3.8-V) and another cell with a Vstart +Vstep voltage. So a VSTEP difference between both cells after a cell reaches 3.8-V. 

    It makes sense that the device will continue working until the voltage reaches 4.2-V, this is the OVP value of the EVM. If the cell balancing LEDs are not turning on. If it reaches this point, cell balancing should occur until the over-voltage cell reaches VFC or (VOV – VHYS_OV), if cell balancing is enabled.

    I would recommend you see our training video explaining cell balancing with the BQ77915:

    https://training.ti.com/how-cell-balancing-feature-works-bq77915

    Best Regards,

    Luis Hernandez Salomon