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WEBENCH® Tools/LM5085: Short circuit VCC to Vin

Evg Bar
Prodigy 20 points
Part Number: LM5085

Tool/software: WEBENCH® Design Tools

Good day E2E,

The power supply was designed through WEBENCH on output voltage 9.6V.
With a load, the power supply produces 10.2V, and with an input voltage Vin 14.4V - sometimes the chip fails with a short circuit Vcc to Vin.

There have been attempts to add a Schottky diode to Vcc (optional diode), this has not solved this problem.

At the bottom schematic of the WEBENCH, and my circuit.

  • 0
    TI__Mastermind 23845 points
    Hi,

    Do you have the normal switching waveform before the part fails?
    Also do you have the layout for the design?

    Thanks
  • 0 in reply to Arief Hernadi
    Prodigy 20 points

    If you load the device with non-inductive load (LM5085 is used to power the digital part of the circuit), the LM5085 works normally. When the device controls the DC motor, the input voltage pulsates, after which the motor at a voltage of 15V and above begins to resonate, then the PFET switching oscillogram is distorted, if the voltage is further increased - the microcircuit fails with Vcc short to Vin. The voltage ripples from the motor were smoothed by an array of input capacitors (20 capacitors — 20.000uF 63v), but this did not solve the problem.

  • 0 in reply to Evg Bar
    TI__Mastermind 23845 points
    Hi,

    Looking at the SW node waveform above it seems that the part is running in DCM (Discontinuous Conduction Mode) meaning the current is small. This is a normal behavior at light load current.

    As far as the motor goes, it seems that this is an inductive type a load, could you try to put a diode between the motor and the output of the LM5085 converter? What is the motor current requirement?

    Thanks
    -Arief