AN136 App note about COT_loop bandwidth

I am reading App note AN-136 " COT Buck Loop bandwidth and Load step response comparison" for good reference .

But I have a question.

The settling time of MP1497S is written as 39.2us on Equation(15), but where should I refer
to this39.2us ?

Isn’t it 47.4us on page 8 Fig8, is it?
If my idea was correct, MP1497S bandwidth calculation should be 14.7KHz where theta=66.5degree.

Best Regards

Hi kanji_shibatani,

Welcome to the MPS Technical Forum. I will look into this for you and provide an update soon.

Hi kanji_shibatani,

Still working on this for you but I wanted to give you an update. This is the graph on Pg 8 and Pg 17 that you and the AN author should be referring to:

Unless I’m mistaken, this is where you and the author are getting your settling times. I am working with our FAE team to validate this measurement and will post an update once available.

Hi Bryan-san
Thank you for your update . AN-136 recommends to use Eq(17), not Eq(13), so it should be
not so important, but if you had find it, please advise.
Thank you for your answer.

Hi kanji_shibatani,

Here’s a response from the author of AN136:

On Figure 8 of the appnote shown below, the right cursor is @ 24mV which is 2% of 1.2V output. The left cursor is at the bottom on the output undershoot. The time delta between cursors is 39.2us which is the approximate settling time. We then use this settling time along with the measured phase margin to calculate/estimate the MP1497S bandwidth.

Remember, the main purpose of the AN136 appnote is to show that the COT part has much better transient response compared to current mode using the same test conditions even if their respective measured bandwidth are almost the same.

Dear Bryan-san
Thank you for your answer. I understood that.
Thank you again.