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BQ76200: BQ76200 bidirectional pre-charger/discharger config and EVM606 cap

BingXie
Intellectual 360 points
Part Number: BQ76200

hi,

i am making a design that using li-iron battery to instead of the Pb battery in vehicle at 24V voltage level.

can i using PCHG funtion for bidirection? which can be used for charge and discharger like the drawing below or is there another way to do it?(Q3 and Q4)

Another question is when i looking at the BQ76200 EVM-606 schematic, there are something i don't understand, why the C1 and C2 are connected there in series? i understand the cap are using for sunnber the over shout, but why two??

Thanks and best regards,

  • 0
    TI__Guru 54715 points

    Hi BingXie,

    1. This may work.  The PCHG is driven with respect to an internal voltage a diode OR of the BAT and PACK pins.  In steady conditions it would match the C31 voltage in your schematic.  When OFF PCHG will match that voltage, when ON it will be about 12V below, see the data sheet for specifications. For precharge during turn on Q3 would be a diode until enhanced, then it would be ON.  For predischarge, as the current increased the voltage across the resistor would drop the source voltages so that they began to turn off.  Q4 would act as a diode, Q3 could drop significant voltage at that current and may get hot. 

    2. C1 and C2 are connected in series so that if one were to short and the other were still good it would not bypass the FETs.  A single component fault would not defeat the FET switching.  The 2 capacitors are often mounted at right angles so that they experience different stresses.

  • 0 in reply to WM5295
    Intellectual 360 points

    Thank you,

    this resolved my issue!