The Bode plot simulation of MPQ8633B using the official steady-state model yields inaccurate results. What parameters/settings should I adjust for correct Bode measurement?
Hello,
The MPQ8633B has a COT control scheme. The switching frequency can change by making adjustments to the off time while preserving the on time of the duty cycle. For this reason, the switching frequency changes given differing loading conditions.
Because of this non-linearity, using a Bode Plot (particularly the gain) to evaluate the stability of this system is not reliable. The phase margin is useful for determining transient stability though by looking at the phase at 0dB.
I would suggest a time domain stability analysis like running a transient response instead.
No problem, happy to help.
Here are some load transient data where VIN = 12V, TA = 25˚C, VOUT = 1V, and Fsw = 800kHz:
