Designing Fsw of hysteretic mode ;MP9486A

DC-DC Power Converters
#1

Hello,

Would you please let me know about how to design the switching frequency of

hysteretic mode converter; MP9486A ?

If I used VIN=60V, VOUT=5V, L=33uH, Iout=1 and if I assume K=0.8 on Equation (2)

of MP9486A data sheet, I would have Fsw = approx.174KHz.

It seems close to data sheet page 7 waveform ( Cout=100uF、stady state Iout=1A: T=around

5.6us)

Is above correct ?

If I want to increase Iout from 1A to 2A, and if I want same Fsw,

I should decrease K from 0.8 to 0.4 by increasing Cout from 100uF to any value?

( I don’t have EVB now in addition to simulation model)

Best Regards

#2

You need an eval board. Per the datasheet you need to alter K but no mention of what factors go into K. The implication in the datasheet is that ESR in the output cap is used to generate a ramp signal to force commutation. The it looks like the switching points are at ±7.5% of nominal but the scope shots show 100mv ripple on 5V which is ±1% so much better than a quick look would lead you to expect. The “adaptive threshold block” must be doing quite a bit to improve the situation.

#3

Hello jshannon,
Thank you for your comment about ESR in the output cap.
I understood that I need eval board.
Thank you again