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TPS54328: backfeed current limit on device

Part Number: TPS54328

Hey team,

I have an application that is taking 12V in to 4V out using the TPS54328DDA, and due to the large output capacitance on this design the 4V output remains after the 12V input goes to 0 and the input side starts to backed current through the switch node of this device.

My question is what is the limit of how much current can pass from the output to the input of this device before it would get damaged? what is the safe limit on that current?


best regards,


  • Hi Saqib,

    Any buck converter with MOSFET highside switch has this kind issue, it depends on how the VIN voltage drops below Vout, in normal application, Vin drops with limited slew rate, the HS body diode will turn on once Vout-Vin differenence higher than Vf of body diode, Vout will tracking Vin drop and you will see dv/dt current which is Cout*dv/dt flows on body diode.

    For example, Cout=220uF, Vin drops at 5V/ms, then I-disc=220u*5V/ms=1.1A. as a rule of thumb, consider it safe current if it's below the HS maximum switching current limit.

    b R
  • HI Saqib,

    From my understanding, the current thru the high side body diode is small. Even if the output cap is big, but it will still be discharged by load and feedback resistor. The current thru high side body diode will be limited by the inductor. The current could not drop abruptly. Current will slowly increase from zero with a changing slew rate due to the discharging of output cap. From my perspective, the concern of using big output cap is on the soft start. The soft start process could be interrupted by current limit if big output cap is used. Thanks!

  • Hey Andy and Anthony,

    Thank you for your feedback, that is good to hear. I appreciate the prompt and thorough responses here. This makes a lot more sense now.

    best regards,

    Saqib Mohammad