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TPS546C20A: WEBENCH POWER DESIGNER - Unable to set switching frequency above 568 kHz, inductor value different than datasheet recommendation

Jim Brinkhurst1
Mastermind 43930 points
Part Number: TPS546C20A

Hi Experts

My customer is creating the following TPS546C20A design in WEBENCH® POWER DESIGNER .

TPS546C20A buck regulator in WEBENCH, Vin min = 5V, Vin max = 5V, Vout = 3.3V, Iload = 6.5A max, Iload min = 6A.

Here are the problems being reported:

  • For some reason it is not allowing me to select a switching frequency of 700kHz.
  • Also I used the datasheet to calculate the switching inductor value, however the WEBENC tool generated a design with a different size inductor.

Best regards,

Jim B

  • +1
    TI__Mastermind 48200 points

     

    The TPS546C20A has a minimum "off" time (Low-side FET On-time) in order to allow the low-side FET to collect current sense data using the low-side FET Rdson.  That is limiting the switching frequency for your 66% duty cycle conversion ratio.

    WeBench is preventing you from creating a design that will not be able to support your desired output voltage due to duty cycle limitations.

    For the inductor, WeBench uses equations similar to those in the datasheet to generate a range of inductor values, and then selects the one which best meets the design goals of size, efficiency, and cost, based on your selection criteria and its available selection of inductors, so it's exact value may not match the value you calculated.