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BQ77915: BQ77915 15-cell consult

Jimmy Zhou95
Intellectual 870 points
Part Number: BQ77915
Other Parts Discussed in Thread: BQ76940, , BQ78350

Customer has used BQ76940 with communication interface. Now they want to implement OV/UV and balancing function. There are some consults for it.

a. Customer only want UV/OV indication signal without external MOS and do not need OCP, OT, UT and OW now. Can they only use DSG/CHG for indication。

b. BQ77915 should support hot plug, ex, when plugging first cell first or third cell first, BQ77915 is not broken. If we use three IC in series, power on first one or second one, BQ77915 should not be damaged.

c. OV indication signal(CHG) should be safely turned on when BQ77915 fail. As in UL2595 standard, battery should not be over-charged in case any of device fails.

  • 0
    TI__Guru* 81034 points

    Hi Jimmy,

    The DSG/CHG pins can be used to indicate a fault, they will just need to translate the voltage levels to the appropriate levels for their controller. 

    The BQ77915 might be able to connect in different order when stacked, but it does have cell balancing FETs internally. I would highly recommend connecting the device power from the bottom up (bottom device first, then middle device, then upper device). 

    I'm not sure I understand the last question. The CHG signal will indicate a OV condition until the cell voltages fall below the OV voltage minus the hysterisis. 

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    TI__Intellectual 870 points

    Hi Matt,

    Still need your help for third question.

    For third questions, I have some details to address. In UL2595 standard, IC safety has been given out at 9.9 and 18.6.1. Overchaging will lead battery to explosion. Considering any BQ77915 failure, CHG should indicate a OV condition. Do you have some comments with it? Thanks! 

    Jimmy

  • 0 in reply to Jimmy Zhou95
    TI__Guru* 81034 points

    Hi Jimmy,

    The UL spec is a system level specification. The BQ77915 can detect and indicate OV. I am not familiar enough with the standard or the customer system to advise whether that is sufficient to meet the requirements.

    Some battery gauge devices (like the BQ78350) have an additional Overcharge Protection feature (in addition to OV), but this might not be required by the UL spec, I'm not sure.

    Best regards,

    Matt