In this question, the last line of the accepted answer states that - That's why the text suggests using 1/5 or 1/10 of the switching frequency as an upper limit in terms of how fast you should design your control circuit to react in order to keep the output voltage constant.

In the above answer, can someone please tell me what components constitute the control circuitry in a typical buck converter circuit (consider a TPS54260 IC)? is the output inductor and capacitor constitute the control circuit or the internal Op-amps present inside the buck converter IC constitute the control circuitry?

What is the control circuitry that the answer is referring? Either the outside output inductor and capacitor or the internal Op-amp and other components present inside internal to the IC?


1 Answer 1


The control circuitry is internal to the IC; on page 12 of the spec it's in the lower and center left of the block diagram. It takes the feedback signal and uses it to adjust the switching frequency or duty cycle, depending on the chip. It may also introduce other control or filtering techniques.

The loop can be considered a sampled system at the switching rate, which is why the answer suggests keeping the dominant pole of the control loop 5-10x slower for stability.

  • \$\begingroup\$ Thank you for the answer. If the control circuitry is internal to the IC, and suppose of Gain and Phase margin needs to be tweaked a little according to our needs, how can we change or modify the control circuitry when all the components of the control circuitry are internal to the IC? \$\endgroup\$
    – user220456
    Commented Nov 4, 2020 at 2:42
  • 1
    \$\begingroup\$ They're not all internal. The SS/TR pin is provided so that you can use an external capacitor to limit the rise time. RT/CLK can be connected to ground through a resistor to modify the switching frequency. The COMP pin is provided so that the loop response can be adjusted with external passive components. Finally, one can connect a small cap from VSENSE to GND to slow down the loop filter, or from VSENSE to Vout to reduce ripple. (The caps on VSENSE aren't explicitly described in the 54260 spec, but are generic techniques that work on some designs.) \$\endgroup\$ Commented Nov 4, 2020 at 13:24

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