I've constructed a circuit model showing an LT1246 current-mode PWM regulator that thinks it's regulating a DC output, but isn't.
The AC stability is gratifying, but is not believable while DC characteristics are up the stump.
The whole circuit responds ~ linearly to a varying clamp on the LT1246 'comp' terminal, showing compliance that includes the intended point of regulation.
The feedback circuit will sort of adjust the point of regulation - shunting it gives open loop gain at the primary current limit, controlled at the 'Isense' pin, as is expected.
The impedances attached to the 'FB' pin are all high enough to be handled by the error amplifier's output capabilities, and the feedback pin is a flat line at 2V497 ~ as expected..
I suppose a separate error amplifier added to the model could get around the problem - but the circuit model's credibility suffers.
There were some early issues with the LT1246 model - duty cycles of
100% being one of them. Is anyone aware of other troubles that could account for the DC error amplifier's behavior?
Mr Engelhardt at Linear Tech is on sabatical till early January, so inquiries there are a little difficult.
RL