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BQ78350: BQ78350 add 2 NMOS on SDA and SCL

Star Xu
Genius 9645 points
Part Number: BQ78350

Hi 

The customer want to add two high-voltage NMOS tubes on communicate line. Add a 5V TVS tube to the communication port. In this way, the self-consumption is reduced, Is it feasible？ 

Thanks

Star

  • 0
    TI__Expert 5090 points

    Hi Star,

    I assume the pullup voltage for the bus is off to the right, is this correct?  Then they need to be careful they get sufficient voltage passed through to the device (which I assume is on the left side of the diagram).  For example, if the bus pullup voltage is 3.3V, then if DOUT is also driven with a 3.3V level, there will be a Vgs=Vth voltage drop from the voltage on the right side to what gets to the left side.  The 2N7002 transistor has a Vth max = 2.5V per the Nexperia datasheet, which means only ~0.8V may get to the device.  Realistically subthreshold operation will allow a higher voltage when current is very low, which is expected when the device is not pulling down the pin.  If they can drive DOUT with a higher voltage, such as 5V or higher, then it will be more robust.

    Thanks,

    Terry