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Original question:

LM5050-1-Q1:

LM5050-1-Q1: LM5050-1-Q1

Firas KHALED
Prodigy 30 points
Part Number: LM5050-1-Q1

Hi,

I used the circuit LM5050Q1MK-1 to drive a Mosfet SQM85N15-19 as shown below. The circuit doesn’t work correctly. The voltage on the VGS of the mosfet is about 4V. this voltage is not enough to drive the mosfet. The losses are therefore so high.

In the datasheet on LM5050Q1, the output voltage shall be between 9-14V.

Have you any idea about the problem?

Thanks


  • 0
    TI__Guru 57737 points

    HI Firas Khaled,

    Can you let us know what is the input voltage that you have tested at ? Is the Gate voltage w.r.t VIN should be as per the curve shown in the datasheet below.

    Have you captured any waveforms. Please share them with us.

    May I know the reason for placing R26 = 100 ohms in the circuit ?

  • 0 in reply to Praveen GD
    Prodigy 30 points

    Thank for your replay.

    This resistor is not mounted, its is short-circuited by 0ohm resistor.

    In fact, the voltage VGS is still 4.125 over all the supply voltage, I tested it from 10V to 70V, it didn’t change as in the datasheet. 

    I've also connect the OFF to the ground, i got the same results.

    Thanks again

  • 0 in reply to Firas KHALED
    TI__Guru 57737 points

    Hi Firas Khaled,

    Please see my response below,

    • Is the IC behavior same from initial power up ? Wanted to understand if the IC initially behaved well and later got damaged.
    • Have you tried verifying the IC which is now on your system on a EVM to see if the Gate voltage is still low. This will help us understand if the issue is with the IC or the circuit.
    • Have you tried replacing the IC on your board with a new IC and check the behavior again ?
    • Do you have provision on your board to place R and C on Vs pin as shown below.