Tool/software: TINA-TI or Spice Models
Hello!
I'm trying to model UCC28950 IC with some special conditions.
My goal is to use an external error amplifier on COMP pin instead of an internal OpAmp.
I made a model like the one in the picture:
And got the following results:
The cursors are attached to show (approximately) the limits within which the duty cycle changes
After IC starts the voltage on COMP pin changes from 5 to 0V. The duty cycle changes from max to min where min duty is set by resistor on TMIN pin. As a result the duty cycle changes in the range of 3.7-1.8V on COMP pin. But the datasheet says that RAMP voltage changes in the range of 0.8-2.8V. The question is, why doesn’t the model work according to the datasheet? It looks like the duty cycle must change in the range of 0.8-2.8V on the COMP pin, but the model shows it doesn’t.
