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BQ77915: MOSFET are over heating

Part Number: BQ77915
Other Parts Discussed in Thread: BQ34Z100-R2

Hi all,

I am working on a BMS project based on the BQ77915 protection IC, and I have made a second revision board. where, as in my first revision, everything is good and the cutoffs are working as expected. In the second revision, I just added the SOC IC (BQ34z100-R2), but for initial testing, I didn't populate the SOC section on the PCB. The MOSFET's are overheating for less current, like 62°C at 2.5A current flow. Second, I found that the charge MOSFET gate signal is ~0.5V (the battery is at 50%), whereas revision 1 has 11.5V with the same battery. My question is:

1. What happens if the discharge operation is carried out without the charge MOSFET enabled in the series FET configuration?

2. If all conditions stated in the datasheet were met, what could be the cause of the charge MOSFET off condition?

Regards,

Janardhan

  • Hi Janardhan,

    The device should turn the CHG FET back on if it detects a current flowing through the body diode of the FET (which is likely the source of the heat).

    Would you be able to observe the voltage between the SRP and SRN pins of the AFE to see if this current is being properly measured.

    The possible faults the device could be experiencing are highlighted below. I recommend checking each of these as well.

    Regards,

    Max Verboncoeur