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BQ77905: 3s charger & protector => BQ24618 & BQ77905: VTB of bq77905 always remains 0V

Part Number: BQ77905
Other Parts Discussed in Thread: BQ24618

Hello,
           
         I testing BQ24618 as an 3's Li-ion charger with BQ77905 as an protector. BQ24618 charger works fine but in bq77905 i observe that VTB pin always stay on 0V.  I think it should be arround 3V.
Because of VTB Pin remains 0v TS Pin is also getting 0V. so bq77905 always remains in fault  & DSG AND CHG turn off. Can anyone tell me what is the issue?

  • Hi Prathamesh,

    Our experts on this device are out this weekend, someone should be able to look into it when they return in the next few days.

    Thanks,

    Terry

  • Hi Prathamesh,

    VTB is pulsed, it is only turned on for the time to make the measurement, then off again.  When checked casually it will look low.  Inspect VTB with a scope, it should approach the AVDD level during the samples. TS will be lower amplitude depending on the temperature of the thermistor.  Be sure the RTS_PU and RTS (thermistor) are not shorted or open, any will cause a permanent fault. Also note in table 8-3 that open wire and current faults can turn off both FET outputs.