Thanks, yes i just logged on and filled in the contact page with the question. I dont have big orders for them so dont know how they will respond.
The point has been in this app note for many years.
___----_____
So...
The attached (LTspice and PNG's) shows a Buck converter with a feedback loop bandwidth of 10kHz
being fed by an input filter with cut
-off frequency of 15.9kHz.
The Buck is perfectly stable, with no problems even after full load to noLoad transient
and vice versa.
This demo's that the VicorPower App Note stipulation that the Input Filter fco should
be below the SMPS's Crossover frequency is inaccurate.
As such, why have they stated this?
After all, if the Buck's bandwidth is 10kHz, then it wont even be able to "see" any resonance at 15.9kHz...
...so why would this be important? The Buck's input impedance will no longer be negative above 10kHz.
Surely as long as the Buck's input impedance is greater than the input filter's output impedance (as
"seen" from the Buck"), -and this over all frequencies equal to or less than the Buck's
crossover frequency....then all will be well?