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TPS54140 switching frequency vs efficiency

nemenem71759
Prodigy 20 points
Other Parts Discussed in Thread: TPS54140, TPS54240

Hi;I am looking for a psu which can give 2A peak current.I have chosen TPS54140.On datasheet a graph( grap) named efficiency vs load current says that max 2a load current is possible (at 1200kHz ).But on EVM datasheet (500Hz) it is given that max 1.5A is possible on Figure 1

My question is :Is there a relationship between switching frequency and efficiency (or max load current)?

 

  • 0
    TI__Guru**** 150620 points

    No, there is no direct relationship between output current and switching frequency.  As switching frequency goes up, there is less ripple current in the inductor which reduces the peak currents in the inductor.  The peak current is what is monitored in the current limiting circuitry.  So, as the ripple current decreases, the peak current will go down and you will be able to get slightly more output current before hitting current limit.  But, most of the time, the ripple current is a percentage of the output current, and from this percentage the inductance is chosen.  So, usually, for higher switching frequencies, the inductance is less which results in the same amount of ripple current.

    There is a relationship between switching frequency and efficiency.  As switching frequency goes up, the switching losses in the FETs and their drivers increase and so efficiency goes down.

    The TPS54140 is a nominal 1.5A part.  This is based on its current limit specification of 1.8A minimum and 2.7A typical.  The minimum specification drives the output current rating for the IC.  So, a typical IC could deliver 2A of output current but no IC could be guaranteed to deliver that much as it is above the 1.8A minimum spec.

    If you need a 2A supply, you should go to the TPS54240.

  • 0 in reply to Chris Glaser
    Prodigy 20 points

    Hi Chris;

    3755.DR1050[1].pdfThank you very much for your response;I want to ask one more question about inductor selection.We wish to use DR1050-220-R inductor from Cooper-Bussman (please check attachment ) instead of MSS1048-223MLB from coilcraft on TPS54140 EVM.We also wish to use DR1050-470-R instead of MSS1048-473MLB .Are these inductors suitable for the designs?

    Thank you very much

  • 0 in reply to nemenem71759
    TI__Guru**** 150620 points

    In general yes, you can use these inductors.

    Please go through the calculations in the applications section of the datasheet.  You enter your system specs at the top of page 28 and then proceed with the calculations.  Which inductor to use depends of your design goals: switching frequency, output current needed, Vin, Vout, efficiency target, etc.