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TPS54428: small chance problem on tps54428

Zhanpeng Li
Intellectual 2130 points
Part Number: TPS54428

Hi Team,

this is brandon.

we met a problem on tps54428 with small chance happening.

we could test the short between VIN-pin and GND-pin. but if we testing with the Multimeter resistance gear for several times, we could find that the device back to normal. is there any insights regard of this kind of issue?

attached the PCB and schemtic below:

br

Brandon

  • 0
    TI__Guru 52105 points

      (Brandon) 

    How are you measuring a "short" between VIN and GND? 

    Are you trying to power up VIN and the sourcing supply is entering current limit as it tries to power-up?

    Or are you using an Ohm-meter on the VIN to GND pin and measuring a low resistance?

    The later test may be misleading, and an artifact of how ohm-meters work along with the semi-conductor effects of MOSFETs.

    Ohm-meters work by driving a small test current between the two terminals and measuring small changes in voltage. That is why using an ohm-meter to measure a capacitor initially reports a very low impedance, and then that impedance slowly rises over time as the capacitor charges and the voltage/current value of resistance increases.

    When measuring a MOSEFT, if there is charge stored on the gate, the MOSFET can have a low resistance. If the high-side MOSFET was left on, for example, and the output capacitors are discharged, or still connected to GND with a load resistance, measuring VIN to GND will report a low resistance.  This is particularly common right after a converter is shut-down rapidly.  When a converter shuts down rapidly, and the driver loses power while the high-side FET is on, it can leave the charge on the gate after the high-side FET driver has turned off, unable to discharge the gate of the high-side FET.

  • 0
    TI__Mastermind 30400 points

    Hello Brandon,

    I looked at your SCH, I do not see an issue with it. 

    For the layout, you can make few improvements, but I do not see how that is related directly to the VIN, GND short you are experiencing? Here are couple comments about the layout:

    • Make the SW trace as short as possible to avoid noise coupling
    • The VIN ground is not layout out in such a way the loop between VIN to GND is going thru a least resistive path.

    Can you please provide a little bit description what is the short you see between VIN and GND? at what conditions? is is showing at all boards or only few...etc?  I am suspecting the input caps to be damaged, but I am not sure of that.

     

    Thanks!

    Tahar