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BQ77905: BQ77905 help check schematic

Star Xu
Genius 9645 points
Part Number: BQ77905

Hi 

Please help check the schematic, the problem is VTB PIN, CHG,DSG no output voltage. We have connected the10K NTC.

We do not need the current sense function. The LD pin is connected to the ground. the schematic not show this modify. 

Waiting for your reply.

Thanks

Star

  • 0
    TI__Genius 11315 points

    Hey Star,

    The thermistor is sampled for temperature measurement as shown in figure 9 of the datasheet. If you are measuring the VTB pin with a meter, it will measure about 0v. If you inspect the signal with an oscilloscope, you should see it pulse high approximately every 120ms.

    DSG and CHG are most likely disabled due to a fault. Depending on how you are connecting your cells, there could be a voltage spike/dip during cell attach that is causing the device to go into OV or UV, and is staying in a fault due to the recovery hysteresis threshold. I recommend connecting the cells starting with BAT- and keeping an eye on transients while connecting. Keep in mind that resetting the device will not clear the faults until the fault recovery conditions are met. 

    Thanks,
    Caleb