About bodeplot of TPS62590.

watanabe

Hi,
My customer has four questions.

Q1.
When the phase margin below 45deg, Do you have concerns such as oscillation?
Q2.
Do you have a method for improving the phase margin?
Q3.
I have changed the feedback capacitor from 22pF to 33pF, And then the phase margin grew bigger.
Why, the phase margin improved?
Q4.
Should I increase the feed-forward capacitor?

Best regards,
Watanabe

over 9 years ago

0 Michael Helmlinger over 9 years ago

TI__Expert 5055 points

Hi,

Please have a look in following application note. There you should find the right information.
www.ti.com/.../slva289a.pdf

What are your conditions like input voltage, output voltage, load current?

Regards,
Michael

0 watanabe over 9 years ago in reply to Michael Helmlinger

Expert 1740 points

Michael-san,

I appriciate for deployment of application notes.

My customer changed to Cff33pf from Cff22pF,
The phase margin has been improved to 40.37deg from 36.62deg.
What is the cause of this phenomenon?

Conditions:

Vin=3.3V Vout=1.2V Iout=0.1A

I will attach the circuit image.

Best regards,

Watanabe

0 Michael Helmlinger over 9 years ago in reply to watanabe

TI__Expert 5055 points

Hi Watanabe-san,

This is described on page 2 and 3 in the application note.
A Cff provides a boost in gain and phase. Increasing the value of Cff shifts the boost to lower frequencies.

So in your application you will get better phase margin due to phase boost at your crossover frequency.

Regards,
Michael

0 watanabe over 9 years ago in reply to Michael Helmlinger

Expert 1740 points

Michael-san,

I really appreciate your quick answer.
I understand to get better phase margin.

Best regards,
Watanabe

Power management

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About bodeplot of TPS62590.