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bq25505 opertion with only primary battery

K. Sasaki14
Guru 10200 points
Other Parts Discussed in Thread: BQ25505

Can bq25505 operate with primary battery only? 

Our customer is considering about the following condition,

-VIN_DC is open

-secondary battery is deep discharge condition. ex) around 0V.

Our customer confirmed the supply current increasing. it is from several hundred uA to 2mA at dozens uA load condition.

If bq25505 is connected to primary battery only (VIN_DC and VBAT_SEC are open), is there possibility of increasing supply current?

Best Regards,

Kohei Sasaki 

  • 0
    TI__Mastermind 20570 points

    The MUX circuitry of the IC can be powered by the primary cell at VBAT_PRI. The /VB_SEC_ON will be pulled high when VBAT_SEC voltage drop below VBAT_OK threshold disconnecting the load from VSTOR. /VB_PRI_ON will be pulled low connecting the load to the primary cell through the external PFET. The IC does not have the control of the current from the primary cell to the load.

    Keep in mind, when the VBAT_SEC voltage dicharged below VBAT_OK, /VB_SEC_ON is pulled low and the load is disconnected to VSTOR. However, VSTOR will continue discharging to power the IC. Since VBAT_SEC is shorted to VSTOR when the voltage on VSTOR is higher than VBAT_UV, the secondary rechargable battery will still be discharging at 325nA typical until VSTOR drop below VBAT_UV.

  • 0 in reply to Jing Zou
    Guru 10200 points

    Jing-san,

    Thank you for your reply.

    According to your answer, bq25505 can operate with primary cell only, it is VIN_DC and VBAT_SEC are open condition.
    Do you have the VBAT_PRI supply current data at the above condition?

    Best Regards,

    Kohei Sasaki

  • 0 in reply to K. Sasaki14
    TI__Mastermind 20570 points
    Sasaki-san,
    The primary cell can only power up the MUX circuitry not the entire IC. Other funcitons of BQ25505 cannot operate with primary cell. The leakage current from the primary cell to the IC can be found in the electrical characteristics table on page 6. We are not able to provide the VBAT_PRI supply current to your load since that is not controlled by our IC.
    Regards,-Jing