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Posted by: Andres Ursueguia on 06/11/2022

PI Expert recommends to put a named C_SOFTSTART if the output voltage is greater than 12V o output capacitance is greater than 100uF. But looking into the Datasheet and examples I cannot find where this C_SOFTSTART is supossed to be placed.

Designing a NON ISOLATED BUCK CONVERTER (230Vin-36Vout-5W).

Thanks in advance...


Submitted by PI-Wrench on 06/13/2022

I understand your frustration - it took me a while to find that information myself. What you're looking for is shown on page 12 of App note AN-70, which covers Link TN2. The link to the application note is shown on the Linkswitch TN2 product page at the PI main web site.

Submitted by Andres Ursueguia on 06/13/2022

Thanks a lot.

I saw this Cap also in the Document RDR-912 Design, but with no mention to it, appart of some simple comment like "C6 is an optional feedforward capacitor which may be required on some designs.".

Normally this CAP is called FEEDFORWARD CAP and affects Zeroes and Poles of the whole system.

A google search of SMPS FEEDFORWARD CAP gives some interesting results to better understand what is the effect of adding this CAP, because it is not obvius this CAP simply ADDS a SoftStart.

Thanks a lot again !!!