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BQ77915EVM-014: DSG and CHG pin issue

Ryan Kelly
Prodigy 10 points
Part Number: BQ77915EVM-014
Other Parts Discussed in Thread: BQ77915,

Hello this is in regards to the BQ77915 IC. I have the evaluation board and tried to discharge three li-ion batteries with three 10ohm power resistors connected in series. The discharge fet was driven low when one of the cells reached 3.1V. After this test both DSG and CHG pins would not go high anymore. VDD pin showed 7.5V. VC5, VC4, VC3, VC2, VC1, and VC0 pins all measured the correct voltage. The board is correctly set up for three cells. All three of the cells were around 3.5V during troubleshooting. Pin 23 and pin 24 both showed 0 volts. The DSG and CHG pins should be high but they are staying low. The voltage measured across pack+ and pack- showed 2.5V but the voltage measured across pack+ and ground showed 10.5V (the voltage of the three cells in series). Is there any reason why after the discharge I would be having this issue? Any other ideas on how to troubleshoot this issue as well? What reasons would the IC not be working after discharging the batteries? Thank you.

  • 0
    TI__Guru 54715 points

    Hi Ryan,

    You have discharged the cells to UV.  The BQ7791500 on the EVM requires load removal for recovery of UV.  Table 5 of the BQ77915 data sheet shows that for UV CHG normally remains on so the battery can be charged. You might check CHG with respect to GND to see if it is actually on.  With a 10.5V battery it might be 9.5 or 10V. 

    If you look at the EVM Schematic in the BQ77915EVM-014 user guide, or figure 26 of the data sheet, with CHG high there will be a voltage divider with the gate resistor, the RLD and RLD_INT.  If the LD pin does not go below VLDT it won't recover from UV.  If PACK- is 8V, LD is probably about 2V and it won't recover.  R30 should drop most of the voltage from CHG, you might inspect the EVM to be sure there is no load remaining on the PACK terminals.  Inspect the EVM circuit for contamination, damage, or unexpected contact with some conductor.

    I think this may solve your issue or let you find it.  Please post what you find.