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WEBENCH® Tools/TPS53315: Cin value selection.

Karthik B
Expert 1310 points

Part Number: TPS53315

Tool/software: WEBENCH® Design Tools

Hi,

How the input capacitor value is selected in the design(by Webench Tool) with,

  • Vin=5V
  • Vout=1V
  • Iout=10A

There is nothing specified in the datasheet also about Cin,Is there any particular formula so that it can be selected(For other designs)? 

can you please help me so that i can use when i do design with different voltage (Vin &Vout) levels.

Regards,

Karthik

  • 0
    TI__Guru**** 191445 points
    Since this is primarily a Webench question, I will move this to the Webench forum. For other cases, you can use this approximation:

    Cin = ( Iout max * 0.25) / (Fsw * Vinripple) where Vinripple is the amount of ripple voltage you want to allow on Vin. As an example for your case lets assume 500 kHz and 100 mV ripple, then Cout minimum is 50 uF. as a reference, the data sheet designs use 4 x 22 uF. That is probably a good rule of thumb for TPS53315.
  • 0 in reply to JohnTucker
    TI__Intellectual 1710 points
    Hi Karthik,

    The above equation by John Tucker can be used for Cin selection in TPS53315.

    However Webench takes Vin ripple factor , Irms current through the capacitor, Voltage derating, power loss and few other parameters into consideration while selecting input capacitor.

    Hence you can set a safety margins up to 150% to 200% on the calculated value of capacitance for better performance. It is also recommended to take Irms and ESR into consideration while selecting the capacitor.

    Regards,
    Vishwanath