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Connecting BQ29312 to à battery pack VS Absolute Maximum Ratings of BQ29312

Charles-Elie Demarty
Intellectual 705 points
Other Parts Discussed in Thread: BQ29312

Hello,

On sluu205 (bq20z80EVM-001), page 12, is  writen : the cells should be connected in following order :
4-Cell (in my case) : 1N (BAT-), 1P, 2P, 3P and 4P (BAT+).

However, in BQ29312 datasheet, is writen : -0.3V < Vcn - Vcn+1 < 8.5V.

My problem is the following : connection between the 3P and 4P, Vcn - Vcn+1=  Vc3 - Vc4 = 3*4V - 0V = 12V. (the input capacitor fixe the voltage)

The Absolute Maximum Rating of Vi isn't respected even with respect connection cell - BQ...

There is there a max time to respect between every connections ?

 

  • 0
    TI__Genius 10225 points

    The connections sequence you described is correct. The sequence must be this way, otherwise there is potential for the internal balancing FET to (it has an absmax Vds of 8.5V) to get damaged. This can happen if the lowest cell, 1N, is attached, then the 3P or 4P cell is attached. This allows the potential for >8.5V to be across one of the balancing FETs if it happens to be open and the rest are closed. You should never see 12V between 3P and 4P. In normal operation, this will voltage will be equivalent to that of a normal cell voltage (i.e. between 3 and 4.2V).

  • 0 in reply to Chase7071949597
    Intellectual 705 points

    Thank for your answer.

    But after rereading, I correct a error : I confused nP and Vcn for : -0.3V < Vcn - Vcn+1 < 8.5V
    So for the connection between the 3P and 4P : Vcn - Vcn+1=  Vc1 - Vc2. And, if I understand, just before connection 4P : Vc1 - Vc2 = 0V and not -12V, because the FET balancing is closed.