Output capacitor of buck converter

[crazy4analog]

I am reading a datasheet and it says output capacitor of buck converter affects its transient response. Can someone help me in understanding this statement?

And how is the transient response measure for buck regulator.

 

[Miguel Gaspar]

Yes it affects. How?
Well the time the buck converter takes to get the final Vo. Like the proportional control settling time.
Please let me know if it respond your question.

 

[sec]

The impedance of your capacitor at your frequency can also affect a lot, you hate to compensate for it in your feedback ... the ESR of a capacitor in switching is a very important thing to consider.

 

[jwfan]

OK, it is a big question. Let me try to answer it.

1. It's important to the whole transfer function of the power stage and will determin the compensation design. (Bandwidth is directly related to transient response)

2. The ESR will help the stability but will generate more ripple. For old Non-linear controls, this ESR will generate ripples which is necessary for control

3. For computing power system, VR12 have detailed information about the output capacitors.

 

[vsemi]

Transient response measurement means load step
You can measure it by change load of output between two certain value

Output cap affect to bandwith so it will affect to transient response (timming and undershoot/overshoot)

 

[masa_2010]

well.

The output capacitor really affect the transient response for buck converter.

The output capacitor and inductor values affect the double pole of LC low pass filter and determine the locations of these poles.This ,off course, determine the final shape of the frequency response for the buck converter.

Another important thing is the ESR of the output capacitor. If you wrote the transfer function for the LC filter you will see that the ESR result in a zero. This zero is a problem cause its location control also the frequency response of buck converter and affect the phase margin of the total system.

The phase margin is an important thing on the closed loop design cause it directly affect the transient time for the buck.

Hope that I helped you and for more answers about this problem you can contact me at :

masa_2010@live.com