TPS57114C-Q1: Guideline for choosing the crossover frequency

Hi There,

I have a question regarding the TPS57114C-Q1 design guideline in the datasheet.

On page 20, it says “use the lower value of Eq 16 or Eq17 as the maximum crossover frequency”. Can you let me know why you recommend a upper limit of the crossover frequency?

If we use this guideline, then the crossover frequency upper limit is only 40 kHz for a 1 Ohm load when the C(out) is high (100uF for example) and the switching frequency is low (2 MHz for example).

We normally choose much higher fc (Eg. 1/20 ~ 1/10 of fsw) to have tighter transient load response.

And I see the TPS57114EVM design doesn’t follow this guideline either. The fc is 90kHz which is above the values calculated from Eq16 and Eq17.

Thakn you for your help in advance,

Sincerely,

Tom