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UCC28711: UCC28711

user3600966
Prodigy 50 points
Part Number: UCC28711
Other Parts Discussed in Thread: UCC28600,

Dear Sirs!

We used yours controller - UCC28600 type  - with wide input range 400-1000Vdc, with multi output voltages. Here we can adjusted (optimize) the voltage control loop at optocoupler feedback.

In the future we would like to use your UCC28711 controller with a higher input range (400-1200Vdc) and with multi output voltages   (Tidu412a).

How can I optimize the controller parameters- to reduce the overshoot on the outputs - or the controller has a self adapted adjusting function .

How many the overshoot,  when the input voltage our the output load change from minimum to maximum of its value. 

Thanks for your answer : Jeno Csizmazia

  • 0
    TI__Mastermind 40230 points
    Hello Jeno,

    Thank you for your interest in using the UCC28711. The UCC28600 controller uses secondary-side regulation which affords a relatively wide degree of loop-compensation flexibility (within limits).

    The UCC28711 (and similar controllers of this family) uses primary-side regulation (PSR) wherein all error voltage processing and loop compensation is built-in to the IC. There is no external way to optimize the controller response. The only option to improve phase margin is to increase the output capacitance above the minimum required capacitance necessary for stability.

    That being said, the amount of overshoot in the usual applications of the UCC28711 is normally less than a few percent, if any. I’m not sure if that percentage would be the same or not in your application, which is not as usual (as a typical battery charger, for instance). However, the UCC28711 operates under peak current mode control, so for a fixed magnetizing inductance and a fixed peak current turn-off threshold, even an instantaneous jump of input voltage from 400 to 1200V should not result in any increase in overshoot. This is because, ideally, only the primary current slope will change (Vin/Lm) but the peak level does not change and no change in output energy results.

    In reality, time delays could allow some higher peak current at the higher input voltage. The UCC28711 uses a feed-forward current out of the CS pin to compensate for this effect and the datasheet describes how to choose the value of Rlc (line compensation) to counteract the effect of turn-off delay. In the usual off-line charger applications, this works very well with a bulk-voltage max:min variation of 5:1 (375V/75V). Your application is only 3:1, so I do not expect any trouble with drastic changes in input line voltage, and no increase in overshoot as a consequence.

    Regards,
    Ulrich