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BQ24170: SRN sense point

Tommy Tzeng
Genius 5780 points
Part Number: BQ24170

Hi Team,

about BQ24170 for 1-cell design, have one problem that need to be clarified.

if the SRN pin15 voltage is lower than the threshold voltage will be recharge? but this pin is the same as battery voltage,and the battery should be fail? right?

  • 0
    TI__Guru**** 166576 points

    Tommy,

    SRN is the negative sense line for the charge current sense resistor and the sense point for the battery voltage.  If the battery voltage sensed at SRN is below the battery regulation voltage (VBATREG), set internally based on the status of the CELL pin, minus the recharge voltage (VRCH) then the charger turns on to charge the battery.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Genius 5780 points

    Hi Jeff,

    got it, i know the process of recharge. but my question is as follow:

    if i set 2-cell by CELL pin seting(cell is floating),so SRN regulation voltage typically is 8.4v, after minus the recharge threshold voltage 140mV~260mV and than start to recharge.

    but i measure TP70A point is 8.37v and start recharge with a different threshold from the datasheet, the voltage difference is only 30mV, is this the right situation?

  • 0 in reply to Tommy Tzeng
    Genius 5780 points

    Hi Team,

    sorry, have any idea or suggestion.

  • 0 in reply to Tommy Tzeng
    TI__Guru**** 166576 points

    Hi Tommy,

    Is the measurement just before charger starting or immediately after?  If after then the voltage is likely be pushed higher due to board and contact resistance.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Genius 5780 points

    Hi Jeff,

    immediately after, you mean the pin15(SRN) voltage(8.37v) i measured was pushed up by the board trace and contact impedance? why? i don't understand..

    so is the threshold voltage correct inside the IC? should can not measure like this?

  • 0 in reply to Tommy Tzeng
    TI__Guru**** 166576 points

    Tommy,

    After charge starts, the voltage sensed at SRN will be ICHG*(Rtrace+Rconnector+Zbattery) +Vbatterycell.  With no charge current flowing, it is only Vbatterycell.

    Regards,

    Jeff