Hi,
I used the excel sheet to design LM25149 buck.
When verifying loop stabilty with generator and oscilloscope, I see quite a shift in crossover frequency compared to calculated values (14KHz measured, however calculated value was around 60KHz). I verified the component values assembled on board and they seem to be correct.
-Cout entered to sheet is correctly derated, also ESR at the specified fsw frequency
Could such a difference be caused by additional capacitance spread across the board outside of the regulation loop? Basically, there are additional bucks cascaded after this converter, each having their own Cin. All are connected to a plane, distance is within 10cm. If I try to de-rate all additional caps on the plane and re-calculate comp values, the measured value is just about 6kHz lower than the calculated.
Is it possible that the shift is caused by "remote" caps outside of the loop or could there by any underlying issue?
Many thanks
Petr
