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Original question:

UCC29950: Pin Configuration

UCC29950: Power management forum

Victor Zykov
Prodigy 45 points
Part Number: UCC29950

Hello.

I'm trying to make 300W AC/DC converter with using ucc29950.
My schematic made according directions from datasheet (pages 36-37). I connected SUFS pin to VCC voltage. VBULK, AC1 and AC2 line resistances are in allowed range. I applied 110V AC Voltage to the input of the schematic, but there wasn't any voltage at PFC_GD pin. When I tried 220V AC, there still wasn't any signal.

At 110V AC there is such voltages at the pins:
1 - GND - 0
2 - GD2 - 0
3 - VCC - 13,2V
4 - SUFG - 0
5 - SUFS - 13,2V
6 - AGND - 0
7 - PS_ON/MD_SEL - 6,8V
8 - VBULK - 520mV
9 - AC2 - 1,04V peak
10 - AC1 - 1,04V peak
11 - LLC_CS - 0
12 - FB - 0
13 - PFC_CS - 0
14 - GD1 - 0
15 - AC_DET - 0
16 - PFC_GD - 0

Could you please help me to resolve that problem?  Where am I wrong?
In addition, it will help me a lot if you write pins voltages at normal operation.

  • 0
    TI__Genius 13660 points
    Hi Victor, I am looking at this question and will get back to you soon. Thanks. ---Teng
  • 0
    TI__Expert 7080 points
    Hi Victor,

    If your schematic was followed our reference design in datasheet page 36~37 . that means you selected Self Bias mode on power up.
    On the other hand , you measured the voltage on MD_SEL /PS_ON pin is 6.8V , that's also proved is Self Bias mode was selected .
    In this mode , the VCC capacitors was charged by start up depletion mode FET until the voltage reach to VCCsb(start) =16.2V.
    Once the voltage on VCC reach to 16.2V , the controller will start PFC and LLC gate driver .
    Please don't connect SUFS pin to VCC if you choose Self Bias mode.

    Usually, we don't measure the voltage on each pin . I guess you were used a multimeter to measure the voltage . but some pin voltage is a varying voltage , such as gate driver pin , so you can only get a average voltage on this pin .

    Hope can help you.
    Thanks.
  • 0 in reply to Jaden Ning
    Prodigy 20 points

    Hello Jaden!
    Thank you very much. The problem was in pins connection.
    I tested only PFC stage and didn't connect the llc_cs pin to ground. It was my mistake, now ucc29950 works perfectly.

    Best regard,
    Victor.

  • 0 in reply to Victor Zikov
    TI__Genius 13660 points
    Glad to hear, I will close this thread. Thanks.