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LM5050-2: power IC

Part Number: LM5050-2
Other Parts Discussed in Thread: TEST, TPS23523

I use LM5050-2 for my power supply for -48V input voltage. I want to know the detail about gate pin. I found this text[ 2A Peak Gate Turn-off Current] in your datasheet. What is it meaning?
Why is this happened? how should I do to prevent the damage of N-channel MOSFET. 

  • Hi Jinlong,

    "2A Peak Gate Turn-off Current" is the pull-down strength of the gate circuit during turn-off under reverse current condition.

    Can you let us know under which test condition the damage happened.? It is only the FET or FET + controller ?

    Please share us the schematic for review.

    Best Regards, Rakesh

  • Hi Rakesh


    I want to use LM5050-2 for -48V power supply. Please tell me what circuits is needed to prevent  the N-channel MOSFET damage when gate  turn off peak current reach 2A . I think some circuits is needed for protect the gate of MOSFET. Do you agree with that?

    Jinlong Liu

  • Hi Jinlong,

    Please use schottky and TVS diodes as per Figure 24 in the datasheet.

    Best Regards, Rakesh

  • Hi Rakesh

    Do you mean Figure 24. Typical +48V Application with Transient Protection?

    as the figure 24 is use for protect pin in and out  when input is shorted, Do you mean that the gate turn-off peak current will reach 2A in this moment?

    So could you tell me why this happen? 

  • Hi Jinlong,

    When reverse current flows in the path, the controller turns-OFF the FET quickly with 2A GATE sink current. Under this condition, the energy stored in the parasitic wiring inductances will be transferred to the rest of the circuit. As a result, the LM5050-2 IN pin will see a negative voltage spike while the OUT pin will see a positive voltage spike. The IN pin can be protected by diode clamping the pin to GND in the negative direction. The OUT pin can be protected with a TVS protection diode, a local bypass capacitor, or both.

    Best Regards, Rakesh

  • Hi Rakesh

    I understood the meaning and reason of 2A peak gate turn off current. The gate of MOSFET will be safe because it is sink current to LM5050-2.Right? 

    another question:
    If I want to design a circuit that can protect rest of circuit from input shorted and reversed Input Voltage, too. 

    How should the circuit be designed to?

    I know that

    Figure 24. Typical +48V Application with Transient Protection

    Figure 25. +48V Application with Reversed Input Voltage (VIN = -48V) Protection

    Thanks

    Jinlong Liu

  • Hi Jinlong,

    I understood the meaning and reason of 2A peak gate turn off current. The gate of MOSFET will be safe because it is sink current to LM5050-2.Right? 

    Yes, it is safe.

    With LM5050-2 should be configured as per Figure 25 for input reverse polarity. Other option is to use LM74700 device

    Best Regards, Rakesh

  • lm74700 can not be used when input voltage higher than 48V. There is no option that use LM74700 device for my application.

    Do you have some recommended device and circuit that is already used by someone and passed the lighting surge test for -48V input power supply?

  • Hi Jinlong,

    Can you please check TPS23523 and let me know.

    Best Regards, Rakesh

  • Hi Rakesh

    Thank you for introduce TPS23523. I will try to use it for new design. 

    Best Regards, Jinlong