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TPS561201: Output Capacitor Value, high frequency zero value

Ue
Genius 17175 points
Part Number: TPS561201

Hi all

My customer is working on a design with the TPS561201, specs are:

12V => 3.9V/0.5A

In their application they have an output load capacitor of up to 200uF, this is definitely higher than the recommended Datasheet value.

They have these questions:

Is it ok to use an output capacitor of 120uF ... 200uF with the TPS561201 ?

If yes: What inductor value should they choose ?

The Datasheet recommends the LC-frequency should be below the "high frequency zero" 

Please provide a value for the "high frequency zero" 

Best regards

Ue

  • 0
    TI__Expert 6425 points

    Hello Ue,

    Actually, 2*22uF ceramric cap is enough.

    If customer insist on using 220uF output cap. it's also ok. 2.2uH inductor is suggested to be used. I also double check on EVM board, and it can work well.

    best regards,

    edwin.

  • 0
    TI__Expert 8245 points
    Hi,

    You can use a larger Cout but there could be potential risks of unstable over a range of input/output. The range of high frequency zero can be estimated using the recommended Lout and Cout value.
  • 0 in reply to Edwin Zang
    TI__Genius 17175 points

    Hello Edwin

    Thank you for the quick reply, thats very helpful indeed. I copy also your additional comments below.

    Best regards

    Ue

    Actually, when the TPS561201 works with 12 Vin and 3.9 Vout @ 0.5A and a small inductor, it works with DCM (Discontinous Conduction) mode. TPS561201 adopts DCAP2 control mode. For DCAP2 control mode, when it works with DCM, it’s always stable. So if the IC works with DCM mode, we don’t need to care about the loop and the zero frequency. 2.2uH or 3.3uH inductor are both ok. If you use smaller inductors the inductor ripple is bigger.