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UCC29910A: SmartBurst Mode not turning off

Nick Naylor
Prodigy 65 points
Part Number: UCC29910A

I actually have more than one question, but let's start with the smartburst. This is on the eval board, I haven't changed or modified anything. Running at 120VAC in and I'm using a resistive decade box for the load. I turn it on at a very small load and it does indeed do the burst mode. However, even up at 90 Watts, it still appears to be bursting. If I zoom in onto the switch waveform, I can definitely see the pulse width changing within the bursts.

Second question, the users guide mentions that you should start into a 0.2A or less load until the output is established. Is this based on the current sense resistor (as some percentage of maximum current) or is it something fixed within the IC?

  • 0
    Prodigy 65 points

                       Q5 Drain - 2mS                                                                                Q5 Drain - 5uS

                                    Q5 Gate - 5mS                                                               Q5 Gate - 5uS

    Ok, here's an update. I looked at the PCF drive right at TP10, the gate of Q5 (main switching FET). That looks OK, no pulsing at all. But if I look at TP11, the drain of Q5, I get what appears to be some sort of burst-mode. Maybe I'm not understanding the functionality of the circuit correctly.

  • 0 in reply to Nick Naylor
    TI__Genius 9140 points

    hello Nick,

    in the  page 8 of datasheet, the light load detect and burst mode control section, the author point out that During the burst, th power train is efficiently operated at close to full power. So my understanding is the burst power should be close to full power.

    for the test of mosfet to judge whether it is in burst mode, I suggest to probe the VGS.

    for the no greater than 0.2A start up, it is related to the current sense for the ocp protection.

  • 0 in reply to David Huang33
    Prodigy 65 points

    I was incorrect in my first assessment. It was not in burst mode. The scope shots are correct and it's doing what a PFC is supposed to do. I'm relatively new to the world of AC (have mostly only done DC/DC).

    My new question is whether or not the input and/or output can be scaled? I know this has been mentioned before in these forums, but since the voltage is sensed through a divider, it should be able to be changed. For example, if I wanted 110V out instead of 84V (assuming the input is high enough) I should just be able to change the divider to achieve that. The only difference being that the pulse width would change. Is this assumption correct?

    This project was handed to me and I'm concerned whether it will work or not. Ultimate goal is 3 phase 480V (we're starting with single phase first) with 375V output at 1kW.

  • 0 in reply to Nick Naylor
    TI__Genius 9140 points

    Hi Nick,

    the assumption is correct.

    Since this controller do not limit the power and input, I suppose it can support 480VAC in 375VDC single phase.

    how will you handle the three phase? the three controllers should not have the same Ground. if you have three DCDC stage to isolate the ground, that should be works.

  • 0 in reply to David Huang33
    Prodigy 65 points

    Thank you for the answer. I haven't gotten to the three phase part yet. I need to get something going on single phase first. Right now, I am working on increasing the power on the evaluation board. After that, I want to try to adjust the output and see how that works.

  • 0 in reply to Nick Naylor
    TI__Genius 9140 points

    ok, so let me close this post. if you have new question, please create a new post.