• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 971 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

UCC28780: start up issue

Zhan Wang
Prodigy 30 points
Part Number: UCC28780

Hello,

I am working on a 100W ACF converter using UCC28780 but found it didn't start up. The waveform below is the start up waveform when I applied 390V DC voltage.

The VHVG ramped up to 17.8V and then dropped to around 11.8V, the run signal went high for around 4.4us. The Vdd voltage is also correct to rise upto 17.8V. However, I didn't find PWML signal started to operate.

The schematic parameters are copied from TI's 100W power adapter reference design.

Does Anyone know what is wrong with my design?

Thanks,

Zhan

  • 0
    TI__Guru 73215 points
    can you use PWML as your oscilloscope channel trig to see if the oscilloscope is triggered?
  • 0 in reply to Hong Huang
    Prodigy 30 points

    Hi Hong,

    Please see the picture below. I used RUN signal to trigger and PWML signal didn't go high after 2us of RUN going to high level.

    Thanks,

    Zhan

  • 0 in reply to Zhan Wang
    TI__Guru 73215 points
    We ask you to use PWML to trigger to make sure PWML status. If PWML does not trigger, this confirms PWML does not have output, but you need to test to confirm if PWML can trigger or not.
  • 0 in reply to Hong Huang
    Prodigy 30 points

    Hi Hong,

    I used PWML as the trigger source and the level is 3.3V, but nothing was captured...

    Here is the long time scale capture waveform using VHGV as trigger source. Ignore the low-frequency 60Hz swing.  The RUN signal went high only at the first time when VHGV dropped to 11.8V..

    Thanks,

    Zhan

  • 0 in reply to Zhan Wang
    TI__Guru 73215 points

    If PWML no pulse is confirmed, then what we know possible reasons are in the table. Basically, there are connections on the UCC28780 resistors or capacitors are not good. So you need to check each connection to make sure ok. Also, you may solder a new IC to exclude the IC issue.

    If all connections are good, and the IC is good, PWML will show at least one pulse after RUN becomes high. If you cannot get the PWML after RUN becomes high, just need to check all connections on IC are correct and the IC is good, and these are what we know based on our experience.