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BQ77915: BQ77915

Ercan Ergin
Prodigy 60 points
Part Number: BQ77915

Hello,

I want to use BQ77915 for 4cell balancing an protection. The voltage references of my batteries seem to be BQ7791501 (acc to Dec2018 version of the daasheet). I have already contacted to my local TI supplier a few days ago. 

On the otherside I want to get direct information, is this version available or is it in the design phase?

Thank you

Ercan

  • 0
    TI__Genius 10830 points
    Hi Ercan,
    bq7791501 is in production and your local TI supplier will be able to provide you parts for your design.
  • 0 in reply to David Hien
    Prodigy 60 points

    Hi everyone,

    As far as I understood from the datasheet, balancing is active while charging. What about discharge?

    The charging current is 1A, but balancing current is 50mA. One of the cells reach the OV and protection stops charging.

    The balancing stops, too. But the cells have not been balanced yet. The voltage difference between cells more than V(CBTH)-V(CBTL)

    Can you offer any solution?

    Thank you,

    Ercan

  • 0 in reply to Ercan Ergin
    TI__Guru* 81034 points
    Hi Ercan,

    Can you provide some more details? Are you able to capture waveforms of the cell voltages for the different cells?
    This video might help explain better what happens as the cells approach OV: www.youtube.com/watch

    Best regards,
    Matt
  • 0 in reply to Matt Sunna
    Prodigy 60 points
    Hi Matt,

    Thank you for the reply. I have already watched that video. If the cell voltages are close to each other, the system works well.

    My questions are:

    If one of the cells reach the OV and the protection stops charging, what happens to balancing? As far as I understand it stops. So the pack is not balanced, right?

    Is there any chance to activate balancing function without charging?

    Our battery pack charge current is 1A, The balance waveforms are same as expected. But do you think that 50mA balancing current is enough? Or external FETs are the only solution?

    What is your suggestion for the ratio of balancing current to charging current?

    I appreciate your help
    Best regards,
    Ercan
  • 0 in reply to Ercan Ergin
    TI__Guru* 81034 points
    Hi Ercan,

    This OV condition is illustrated in the video at around the 4:30 mark. Balancing will occur in OV even though the charging current has stopped. The OV cell will balance if CBI is enabled.

    It is possible to activate balancing without charging by configuring the device as an upper device of a stacked solution. However, you would lose the overcurrent detection fault protection by configuring it in this way. Some users who do not need current sense do use the device in this way with cell balancing always enabled regardless of current direction.

    The bq77915 has a resistor programmable behavior on the OCDP pin. If the resistor value is set to 10M ohm the current will be ignored for balancing since the part thinks it is an upper device in a stack. Cell balancing can then be controlled by the CBI pin (and the voltages). SRP and SRN are connected to VSS on the board, no current protection is expected.

    I don't have a good guideline as to the ratio of balance current to charging current. This really depends on your battery and how much you expect the cells to get out of balance.

    Best regards,
    Matt