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BQ78350: BQ78350+BQ76930 abnormal power consumption

Part Number: BQ78350
Other Parts Discussed in Thread: BQ76930, BQ76200

Hi

The customer design with BQ78350+BQ76930 with 8 series cells. They found the 7th cell have 0.7mA current consumption.

When removed the cell balance circuit still have 0.7mA current.

Attached the schematic for your reference.

8741.BQ76930+BQ78350修改.pdf

Please give some suggestions.

Thanks

Star

  • Hi Star,

    I am not sure why they are seeing 0.7mA on Cell 7 - are they measuring the current across by looking at the voltage drop on RF7? Have they tried replacing the IC?

    I do see a few things in the schematic that may cause additional problems:

    • Pin 11 and 12 of the device should connect directly to the CAP2 pin (should not use 1k resistors).
    • It is good to use a filter capacitor on the Alert pin in addition to the pull-down resistor. This can prevent false ALERT_OVRD protection triggers due to noise. See the BQ769x0 schematic video for more information: https://training.ti.com/how-create-schematic-bq76920-bq76930-and-bq76940 
    • The CAP1 and CAP2 pins should not connect to additional circuitry. It looks like CAP1 is being used to drive the base of Q1 to enable LEDs.
    • The BQ76930 is driving several parallel protection FETs. It is recommended to use individual gate resistors on each FET to prevent oscillations which is a common issue when controlling many FETs in parallel. Also, since many FETs are in parallel, a FET driver like the BQ76200 may be needed. These resources may be helpful:

    Best regards,

    Matt