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LM5146-Q1: Negative Buck Converter Using LM5146-Q - HO MOSFET damage

Julia Jonsson
Prodigy 30 points
Part Number: LM5146-Q1


I am working on the design of a negative buck converter that uses the LM5146-Q1 as the driver. The converter has been operating successfully in approximately 50 systems. However, in 3 systems, the high-side MOSFET was damaged—possibly after the HO driver failed.

My questions for TI are:

  1. What could be the root cause of the damage in these three units?
  2. What internal behavior in the driver circuit could lead to MOSFET damage through the gate?

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  • 0
    TI__Guru* 77752 points

    Hi Julia,

    Have you got a completed quickstart calculator for this design? Stability is more challenging with negative Vout. Also, these are very capacitive MOSFETs - please send the gate and SW waveforms. Remove the low-side FET gate resistor.

    Regards,

    Tim

  • 0
    Prodigy 30 points

    Hi Timothy, 

    Thank you for your reply.
    Please see the attached waveforms: V_G–GND (pink), V_SW–GND (yellow), V_GS (green), and V_OUT (blue), for V_OUT = 9 V.


    The figure below shows a persistent mode, Vout adjusted from 3 V to 9 V.

    The previous designer of this circuit used the Quickstart Calculator, and we have not experienced any stability issues—except when operating with an external current-control loop. 
    Do you see any design flaw that could lead to damage of the upper MOSFET’s gate?
    What kind of disturbance could have happened?
    Best regards, Julia