LM5177: Why would you use "Power Save Mode" vs. "Forced PWM Mode" / "Continuous Conduction Mode"?

Hi Paul,

as the name says in FPWM (forced PWM mode) the device runs always with a fixed frequency independent of the load and input and output voltage condition.

This also means that if in one cycle more energy is shifted to the output then in will be push back to the input in the next cycle. Furthermore if the output is higher then the input the energy conversion direction is inverted and energy is moved from the output to the input. 

In PSM mode this will not happen and the controller stops switching and skips switching cycles. This of course saves power (PSM Mode).
On the other hand you do not have a fixed frequency (in this condition) any more.

Also the ripple on the output voltage can be increased in this mode.

Best regards,

 Stefan

Thank you, I understand that is what those modes are.

But WHY would I choose the FPWM mode?
Under what circumstance would I use it?
Why would I not always want the "power saving" mode?

It is simply to get less ripple?  Or is FPWM better for high current loads?
Is there any reason to switch back and forth between modes?

Hi Paul,

But WHY would I choose the FPWM mode?

- Fixed frequency

- bidirectional operation mode

- fastest response on load jumps

- lowest output voltage ripple

PSM Mode:

- better efficiency in lower load

- no backward operation.

Switching of the mode is possible and can be used to get the best performance but this of course depends on the application requirements.

Best regards,

 Stefan

Thanks, Stefan.
"fastest response on load jumps" vs. "better efficiency in lower load" seems to be the trade off that applies to my application.

Is there any data available comparing the load transient response of the two modes?