How to calculate Loop Bandwith (MP9942 - current mode)

[frank.koenig]

Hi
Is there a way to calculate the Loop Bandwidth.
This is my schematic

It would be great, if there is a formula.

Thanks

Kind regards
Frank

[Kareem]

Hi Frank, the datasheet has typical values for the FB and RT resistors for a 5V out application that put the bandwidth in the correct place. Can you try these values?

[frank.koenig]

Hie Kareem,
thanks but with the proposal from the datasheet, the required phase margin (for a stable system) is smaller than 45 degree.

[frank.koenig]

Here is my solution (best compromise).

Instead of 22.1kOhm I take a 22kOhm resitor.
So I have values from E48 row.

[Kareem]

Hi Frank, the reason the phase margin is reduced in your original setup is because of the pole introduced in the feedback loop with C6.

If you simulate the recommended values from the datasheet for Vo = 5V, you should see a healthy phase margin of roughly 53 degrees.

[frank.koenig]

Hi Kareem
I choose this variant, because I want to use your MPS MPL4030 22uH Inductor.

[frank.koenig]

Is this also possible, because “Phase Margin” is smaller than 45degree?

[mpsnow.bryan]

Hi Frank,

It is possible but we would still recommend keeping the phase margin above 45 degrees for better stability.