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BQ77905: 84s Battery pack protection

user4619253
Prodigy 50 points
Part Number:

Hi,

    In our project, the number of series  litium cells is up to 84, I wonder if there is any solution for stack up of bq77905 for this application.

    I understand that the maximum series  number for  bq77905 is 20s.

   Can I use a isolator between bq77905's daisy chain signal  to avoid high volt of up to 84s? 

  • 0
    Prodigy 50 points

    user4619253 said:

    Part Number: BQ77905

    Hi,

        In our project, the number of series  litium cells is up to 84, I wonder if there is any solution for stack up of bq77905 for this application.

        I understand that the maximum series  number for  bq77905 is 20s.

       Can I use a isolator between bq77905's daisy chain signal  to avoid high volt of up to 84s? 

     Is there any solution for my application? Thanks

  • 0 in reply to user4619253
    TI__Expert 4640 points
    Hi,

    The bq77905 was not tested beyond 20S, but can be stacked multiple times. Some things to keep in mind is that there may be a long delay when the higher stacked devices trigger a fault and pass down the signal from CTRC / CTRD all the way down to CHG and DSG pins to drive open the FETs. Keep that in mind. Additionally keep in mind of components, if you are using the LD pin for load detect you may need a higher resistor as when there is a fault the pack - may be drawn really high. Lastly, keep in mind on hot plug, when you first connect the cells.

    Thanks

    Miguel
  • 0 in reply to Miguel Angel Rios
    Prodigy 50 points
    From the datasheet, I understand that the bq77905 can be used maximum 20s even by being stacked.
    "Up to 4 devices can be stacked to support ≥6S cell configuration, providing protections up to 20S cell configuration"
    For our project, I understand that 84s is quite beyond the 20s. What I care about is that if there is a way to avoid high common mode voltage from CTRC / CTRD all the way down to CHG and DSG pins for our application. For example, by using a digital isolator or photo-coupler between the CTRC / CTRD and CHG and DSG pins.
  • 0 in reply to Miguel Angel Rios
    Prodigy 50 points
    From the datasheet, I understand that the bq77905 can be used maximum 20s even by being stacked.
    "Up to 4 devices can be stacked to support ≥6S cell configuration, providing protections up to 20S cell configuration"
    For our project, I understand that 84s is quite beyond the 20s. What I care about is that if there is a way to avoid high common mode voltage from CTRC / CTRD all the way down to CHG and DSG pins for our application. For example, by using a digital isolator or photo-coupler between the CTRC / CTRD and CHG and DSG pins.
  • 0 in reply to Miguel Angel Rios
    Prodigy 50 points
    From the datasheet, I understand that the bq77905 can be used maximum 20s even by being stacked.
    "Up to 4 devices can be stacked to support ≥6S cell configuration, providing protections up to 20S cell configuration"
    For our project, I understand that 84s is quite beyond the 20s. What I care about is that if there is a way to avoid high common mode voltage from CTRC / CTRD all the way down to CHG and DSG pins for our application. For example, by using a digital isolator or photo-coupler between the CTRC / CTRD and CHG and DSG pins.
  • 0 in reply to user4619253
    TI__Expert 4640 points
    It doesn't appear that there would be any benefit to using a digital isolator. The part is designed to work with common mode voltages

    Thanks

    Miguel