Switch Mode DC/DC Power Supply Design

[varunkoganti]

Preface-

I am designing a drone, My choice for stepping down voltage is to use a DC/DC switching converter, after using the parametric search of Digi-key, I selected TPS54495RSAT‎ as my SMPS.
TPS54495RSAT‎ is a dual SMPS capable of 4A@Output1 & 2A@Output2. My SMPS design will output 5V,4A@output1 & 3v3,2A@output2.
It has 2 soft start pins, as per my understanding from datasheet they are used to protect devices ie to reduce inrush current during startup as the SMPS switches with full PWM.

Problem Statement -
What should my soft start time be?
10ms ? 50ms? 100ms? this timing is what determines my capacitor value connected.



Hyperlink to the part(TPS54495RSAT‎ ).
https://www.digikey.in/en/products/detail/TPS54495RSAT/296-TPS54495RSATCT-ND/4291940?itemSeq=386099797

[jwet]

My advice is to commit to a PCB and build it.  It will probably work ok but you might find some anomalies that you can investigate and correct.  SMPS are very layout senstive- minimize high current loop area and have very low impedance grounds especially at these current levels.  A 25 milliohm resistance (like a fuse) creates a 100 mV drop at 4 amps.

[palpurul]

You can change your soft-start time later in your design.
Just slap a 0805 cap footprint from ss to GND and test what works best for your design.
4A is not low just focus on layout I think.