I'm looking at the LM2596S datasheet and notice that on page 7 (figure 3) it recommends a "feedforward" capacitor for the adjustable variant.
The example schematic on page 9 shows a capacitor labelled CFF:
Underneath there is a note saying "CFF - See Application Information Section". I have looked through the application information section and searched the PDF for variants of "feedforward" and "CFF" but it does not appear to be mentioned anywhere else.
What is the function of this capacitor? Why is it only recommended for the ADJ variant of the buck converter IC?
My guess is that it acts to negate some of the resistance of R2 during transients, since current will flow across the capacitor when there is a voltage differential. Perhaps this is to speed up the feedback response time, but I'm not sure.
If the feedback voltage is instead provided by an opamp and shunt resistor for constant-current operation, such as in the example below, should this capacitor be placed in parallel with the shunt?
simulate this circuit – Schematic created using CircuitLab