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BQ25703A: How to config the battery configuration?

user5821506
Prodigy 190 points
Part Number: BQ25703A

Hi

Referring to the specification of BQ25073A, the configuration of 4 cells requires the voltage of CELL_BATPRESZ voltage to be 75% of VDDA, but referring to the DEMO board, its voltage is only 64%of VDDA , is there something wrong with the EVM board design? My product is 4 batteries(4.35V each cell), and the resistor I use is 56K. Is there any problem?Do i need to change it to another value?

The Battery Cell Configuration：

The EVM：

My Schematic：

How to choose the resistor at CELL_BATPRESZ  when the max charger voltage is 17.4V ( 4-cell configuration , 4.35V )?

  • 0
    TI__Expert 5330 points

    Hello,

    Please design to the tolerances of the datasheet, i.e. 75% nominal, 68.4% min as you show.

    The EVM tries to use resistor combinations in a way that will require fewer jumpers, so it doesn't hit each setting as closely as it could, although I believe that it is still within tolerance

    For 4 cells on the EVM, attach JP2 and JP3 and leave J4 open.  JP2 shorts out R24, so it has no effect.  Then with JP2 and JP3 installed, this creates R20 || R21, and this combination is in series with R28, so that the resistor-divider ratio is R28 / (R28 + ( R20 || R21) ). Subbing R20 = 120K, R21 = 64.9K and R28 = 100K.

    R20 || R21 = 1 / (1/R20 + 1/R21) = 42.1 K

    Then 100K / 142.1K = 70.4%

    This isn't exactly at 75%, but it is within the tolerance since it is > 68.4%. 

    That said, you should try to set your divider up to get as close to 75% as possible.

    Regards,

    Steve

  • 0 in reply to Steve Preissig
    Prodigy 190 points

    Thank you very much.

    I miscalculated the resistor value.