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LM5050-2 / Behavior of VGATE at start-up

S.Satoshi
Guru 21685 points
Other Parts Discussed in Thread: LM5050-2

Hi All,

Our customer has evaluated LM5050-2 at momentary power failure and then they confirmed the VGATE is not fully discharged. I believe that this is due to the device is stopped before fully discharging VGATE. Next they confirmed the VGAET is dropped to zero voltage at restart timing. Does this mean that the LM5050-2 discharged VGATE at start-up first and then start to regulate FET?

Best Regards,

Sonoki / Japan Disty

  • 0
    Guru 21685 points

    Hi All,

    I'm looking forward to your response.

    Best Regards,

    Sonoki / Japan Disty

  • 0 in reply to S.Satoshi
    TI__Intellectual 2980 points

    Sonoki- san,

     When  the input power fails abruptly... as your case is , the MOSFET current reverses from Vout to Vin ,  Now the  voltage across the LM5050-2 IN and OUT pins is more negative than the VSD(REV) voltage of -27 mV (typical), the LM5050-2 will quickly discharge the MOSFET gate through a strong GATE to IN pin discharge transistor.

     So after power fails, VGate will be discharged as explained above and at every start up   it will  regulate the MOSFET gate-to-source voltage if the voltage across the MOSFET source and drain pins falls below the VSD(REG) voltage of 27 mV (typical).

    Let me know if you have further question.

    Regards

    Dinesh

  • 0 in reply to Dinesh Kumar6
    Guru 21685 points

    Dinesh-san,

    Thank you for your response. Now I'm assuming that the VIN fall to 0V quickly then the MOSFET gate can not be fully discharged and the gate voltage is remained. But you also commented that that the gate will be discharged at every start up, so I understand that the remaining charge at gate is discharged at every start up.

    Is my understanding correct?

     

    Best Regards,

    Sonoki