Constant off time control and RHPZ

[cupoftea]

Page 19 of the LM3421 datasheet says there are issues with the RHPZ.
But LM3421 is a constant off time controller (COT).
COT controlled SMPS dont have RHPZ's.
So why does it say it?

LM3421

https://www.ti.com/lit/ds/symlink/lm3421.pdf

 

[mtwieg]

COT controlled SMPS dont have RHPZ's.

Yes they do. Not sure where this myth originated but constant on/off time control has no effect on the RHPZ (or any poles and zeros).

 

[cupoftea]

Thanks, but,
Page 8 (actually 9th page) of the below "current mode control" by Venable (you have to give your name and email to download it) says that Constant Off time control makes the RHPZ frequency higher, and so its less of an issue.

Principle of Current Mode Control

This white paper details the principle of current-mode control, how it is supposed to work, and how to test a current-mode converter.

www.venableinstruments.com

But yes i see we have spoken of this before..

Solving the RHPZ problem of boost converter using Fixed Off-time PWM Control

Hey guys, I've read this pdf file which I saw in one thread here. https://www.venable.biz/uploads/files/05-Technical-Paper-Current-Mode-Control.pdf It discusses about minimizing the RHPZ effects with the use of Fixed off-time control. It discusses it based on a time-domain figure which looks...

www.edaboard.com

 

[Easy peasy]

Fixed off time control has it's limitations, as soon as the on time allows for continuous current in the magnetic you are in RHPZ territory . . .