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TPS56837: Current Ripple w.r.t. Switching Frequency

Siddhaarth R
Prodigy 20 points
Part Number: TPS56837

Tool/software:

Hi Team,

We are working with a high speed switching load which operates at 8V, The 8V Domain is supplied from a stable 24V Power domain.

While using a TPS56837RPAR Buck Converter, we observed peak currents of around 6A, This was observed with a switching frequency of 500kHz.

Upon experimenting with a Switching frequency of 800kHz by just changing the value of the resistor connected to MODE pin, We observed that the peak current in the 8V Domain reduced drastically to around 2A. We have observed that the mean current remains almost the same while the difference in peaks is drastic. We want to understand the effect of switching frequency on this high switching load. Please do let us know the relation b/w the switching frequency and output current ripple.

I have attached the schematics in our design and the observed peaks for your reference.

Switching Frequency 500KHz 800kHz
Peak Current 6A 1.85A
Mean Current 160.7mA 150.5mA
Observed Waveform
  • 0
    TI__Intellectual 2620 points

    Hello Siddhaarth,

    Please refer the Eqn 8 in the datasheet calculating IL- peak to peak current, which is inversely proportional to Fsw.

    hence you will surely see the decrease in peak current.

     

    -Hitesh.

  • 0 in reply to Hitesh Chandwani
    Prodigy 20 points

    Hi Hitesh,

    Thanks for your feedback.

    Could you please review the above schematic and please let us know if the schematic is appropriate for an input voltage of 24V, output voltage of 8V and an average load current of 150 - 200mA?

    Would you also recommend any snubber circuit across the output inductor for the same?

  • 0 in reply to Siddhaarth R
    TI__Intellectual 2620 points

    Hello Siddhaarth,

    schematic looks correct,

    Just mode pin resistor you can define depending upon the frequency of interest and the current limit you need in your circuit.

    check Table 6-1 in datasheet for mode pin resistor.

    You can even try for 1.2Mhz if your board layout supports that, which may improve your transients.

    -Hitesh