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Other Parts Discussed in Thread: LM3743

Hi

I read the TI paper about AN-1997 Error Amplifier Limitations in High Performance Regulator Applications, and I have some questions

1.)in this figure I don't understand why the DC gain (Low frequency) can't match the ideal compensator, in the high frequency why the compensator would follow the open-lop EA Gain

2.) If I want to use marhcad to simulate the type III compensator (nonideal EA), is my formula wrong? the green line can not match the figure 5.

over 4 years ago

0 Dorian Brillet de Cande over 4 years ago

TI__Genius 14876 points

Hello User,

I am not sure what is the App note you are referring to.

Can you share it here ?

Did you use the equation from the App Note ?

Let me know.
Thanks a lot!

Regards,
Dorian

0 J over 4 years ago in reply to Dorian Brillet de Cande

Expert 1065 points

HI

This is the app note link I use the equation from the APP Note

0 Dorian Brillet de Cande over 4 years ago in reply to J

TI__Genius 14876 points

Hello user,

Did you use same value as in the App Note? Or did you use something specific to your Application?

How does this relate to your use of LM3743?

I would first check, the left part of the non ideal equation.

I am trying to understand what you are trrying to achieve to best help you here.

Thanks a lot!

Reagrds,
Dorian

0 J over 4 years ago in reply to Dorian Brillet de Cande

Expert 1065 points

Hi

I think the EA in the low frequency should be the same with the ideal compensator, but in this document the ideal EA and non-ideal EA in the low frequency can not match, I can't understand why?

0 Dorian Brillet de Cande over 4 years ago in reply to J

TI__Genius 14876 points

Hello user,

It is specified in the App note that "The frequency range is purposely wide to capture the low and high frequency regions where the non-ideal EA most affects the compensator characteristic."

This means that the Equation 7 is a good simplification for frequencies in the range of 10^2 to 10 ^7.

It is also very likely that the (Zi//Zf)/Rfb2 factor is not neglectable at very low frequency.

Thanks a lot!

Regards,
Dorian

0 J over 4 years ago in reply to Dorian Brillet de Cande

Expert 1065 points

I got it

Thanks

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