TPS40200: Application note slva301

Ram Sivanehru

Part Number: TPS40200

Hi,

I am referring the application note slva301 for designing the compensator network for the buck converter.

could some one please explain to me the following equation in page 18; how did they derive it, ,and how did they come up with the answer 1.35.

Thank you

Siva

over 7 years ago

0 JohnTucker over 7 years ago

TI__Guru**** 191445 points

Page 18 contains several equations. Which one are you referring to?

0 Ram Sivanehru over 7 years ago in reply to JohnTucker

Prodigy 90 points

Hi John,

I have placed the equation, somehow it isn't there anymore.

Step 6 : calculating the required gain of the compensator at the desired crossover frequency.

Thanks

Siva

0 JohnTucker over 7 years ago in reply to Ram Sivanehru

TI__Guru**** 191445 points

Normally i would assign this to the app note author, but he is not with TI any longer. I can tell you generally what that equation is about. At crossover by definition the loop gain is unity (0 dB). To achieve this, the gain of the compensated error amplifier must be equal and opposite of the gain of the modulator and output filter. That is what is being calculated in step 6.

0 Ram Sivanehru over 7 years ago in reply to JohnTucker

Prodigy 90 points

Thanks,

I think the author used one (1) capacitor CCM filter response (page 32) equation, so now I know where the equation comes from.

The LC filter response depends on the number of capacitors (1, 2, and 3), when you lump them together the response is different.

In step 6, I have managed to get answer 1.35, only when I placed the value for ESR equal to 10.5m and for C = 247u (220+22+5).

I need to know the reasons behind the values selection for the capacitor and the ESR.

Siva

0 JohnTucker over 7 years ago in reply to Ram Sivanehru

TI__Guru**** 191445 points

Those are just that values that the author chose. I doubt there is any specific reason for it. Since the author is no longer here, it is impossible to know why he chose them.

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TPS40200: Application note slva301