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BQ25505: VSTOR without primary battery

Diana Hui
Prodigy 10 points
Part Number: BQ25505

Hi,

My current design is using BQ25505, but the datasheet does not state MUX signal if primary battery is not connected. Will VSTOR keep internal reference to the secondary battery level even if it is lower than the VBAT_OK_PROG when Primary battery is detached? Thank you.

Regards,

Diana

  • 0
    TI__Guru*** 148545 points

    Hi Diana,

    The MUX output pins are powered from the diode OR of VBAT_PRI or VSTOR.  Other than that VBAT_PRI has no effect on charger IC operation.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 10 points

    Hi Jeff,

    Thank you for answering, here is another follow up question. Does the VSTOR keep output VBAT_SEC when VIN does not have enough input power and VBAT_SEC falls below VBAT_OK?

    Regards,

    Diana

  • 0 in reply to Diana Hui
    TI__Guru*** 148545 points

    Hi Diana,

    No.  There is a PFET that connects VSTOR=VBAT_SEC.  If there isn't enough power at VIN_DC to drive the load at VSTOR and charge the battery at VBAT_SEC, both VSTOR and VBAT_SEC voltages fall.  VBAT_OK is the output of comparator monitoring VSTOR voltage and has no effect on charging.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 10 points

    Hi Jeff,

    Will the VSTOR keep output of VBAT_SEC even if the VBAT_SEC falls below VBAT_OK_PROG? Or will the MUX stop working if there are no VBAT_PRI? Thank you.

    Regards,

    Diana

  • 0 in reply to Diana Hui
    TI__Guru*** 148545 points

    Diana,

    VBAT_OK is the output of comparator that reports where the VSTOR=VBAT_SEC in relation to the VBAT_OK_PROG and HYS resistors.  It does not affect the operation of the converter.  The MUX is powered by a diode OR of VBAT_SEC and VBAT_PRI.  As long as VBAT_SEC is up, the MUX is powered.

    Regards,

    Jeff