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LM25088-Q1: broken MOSFET and bead

Dexter Choi
Expert 2795 points
Part Number: LM25088-Q1

Dear Sir,

my customer is using LM25088MH-1 for inverting as below spec.

Vin: 12V

Vout: -2.5V

Iout: -2.5A

sometimes it happened broken MOSFET(Q2) and Bead(FB485,FB486) on testing. 

could you help check attached schematic?

  • 0
    TI__Mastermind 25590 points

    Dexter,

    I assume you mean Q2.

    Are the ferrites or FET overheating? Does the circuit violate the absolute max specs of the FET or ferrites? What other clues can you give me about what is causing the damage?

    -Sam

  • 0 in reply to Samuel Jaffe
    Expert 2795 points

    Hi Sam,

    please check it below clues.

    1. It is presumed that the FET and Bead are burnt out after overheating due to overcurrent.

    2. FET, Bead are not a problem in capacity. (FET 35A, -55℃~155℃ / Bead 600Ω 1A * 2ea)

    3. The problem occurs only after the vehicle is mounted for field test.

    Thanks.

  • 0 in reply to Dexter Choi
    TI__Mastermind 25590 points

    Dexter,

    1. What is causing the overcurrent? Is the load shorting? Or are you thinking the FET breaks, shorts VIN to VOUT, then the ferrite overheats from the current?

    2. The output current is 2.5A as you stated. That means each ferrite bead gets 1.25A if evenly shared (will not be perfectly shared). You will need probably at least 1.5A ferrite beads to handle this current.

    3. If true, this means the device is susceptible to conditions only seen in field tests. What conditions are tested in the field but not in the lab? Load dump, cold crank...? And does this fail after a particular condition?

    -Sam