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Original question:

UCC28950: Question about operation

UCC28950: PMP8740 pulse generation issue

Nidheesh BR
Expert 1295 points
Part Number: UCC28950
Other Parts Discussed in Thread: PMP8740,

Hi,

I was trying to develop PMP8740 2KW full bridge dc-dc converter. But currently, bypassing the control card used by TI.

I have completed the power section and it is working well with external PWM signals.

Now I want to run it with UCC28950 on the board. But when I am trying to turn it on it is not producing any gate pulses.(the Current transformer is not attached, means ct+ and ct- are kept open )

I have checked the basic condition to turn on.

Vdd pin voltage > UVLO

SS/EN capacitor voltage >0.55 V(around 4.5V is coming)

The 5V ref is available and temp <140 degrees.

still, it is not producing pulses.

So what are the minimal requirements to turn it on(tested with no load)?

whether CT is mandatory to turn it on?

Regards.

Nidheesh.

  • 0
    TI__Expert 3460 points

    Dear Nidheesh,

    I propose you to check the COMP pin signal output  level.

    In addition, if you still have not output pulse, could you please attach your SCH for review.

    Thanks 

  • 0 in reply to Bliss Zhou
    Expert 1295 points

    Dear Bliss,

    thank you for your feedback.

    Now I have checked EA+ pin and is noticed that the voltage at that pin is near to zero. So I disconnected the feedback by removing D1 and D3 then it is started giving pulses(I was running without any power circuit on).

    when I am connecting D1 D3 back again pulses are vanishing.

    what will be the probable reason for this?

    Regards.

    Nidheesh

  • 0 in reply to Nidheesh BR
    TI__Expert 3460 points
    Dear Nidheesh,

    According to PMP8740 EVM, the COMP voltage level follow EA+. There is not pules if the comp is close to 0V. I think you need to check the U1A and U1B output voltage why is closed to 0V.


    thanks
  • 0 in reply to Bliss Zhou
    Expert 1295 points

    Dear Blizz,

    Thank you for your valuable information.

    Yes, you are right. It was an issue from U1A and U1B. When I corrected the feedback from U1 the issue got resolved.

    Now I tested up to 49A at 32V. Still, I am not using CT and it is working well. So whether the CT is mandatory or not?

    Regards

    Nidheesh

  • 0 in reply to Nidheesh BR
    TI__Expert 3460 points

    Dear Nidheesh,

    It is such pleased that I hear from your news. CT or not, it depends on you select the control mode is PCM(peak current mode) or VMC( voltage mode control).

    it must be used if you select PCM.  CT is not mandatory if you select the VMC but Primary current protect function is missed.

    in addition, attention please the CT function as below.

    The signal from the current sense pin is used for cycle-by-cycle current limit, peak-current mode control, lightload efficiency management and setting the delay time for outputs OUTA, OUTB, OUTC, OUTD and delay time for outputs OUTE, OUTF.

  • 0 in reply to Bliss Zhou
    Expert 1295 points

    Thank you so much Bliss.

    I will do it accorndingly.

    Regards

    Nidheesh