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UCC28070: UCC28070

Stephen Mantz
Prodigy 80 points
Part Number: UCC28070

Designed a 3Kw PFC with half bridge following.

1] The values shown in the Excel design tool spread sheet are confusing at best. Example it shows RTA and RTB to have values of  "-1.41e+03" How can there be a minus sign?

2] The values f many parts are way different from typical TI schematics.

3] For our design the current sensing XFR [Line 39] is shown with a turns ratio of 1:491. There is no information regarding what turns ratio should be used for a particualr power output design.

4] Some designs show a diode + 33v zener acrosso the current sense secondary, others show a snubber (4.7pF + 1K) yet the spreadsheet calls for 100R for 3Kw...confusing so which is correct? Snubber or diode snubber?

5] In line 84 the value called for is 5.9E-10 but in line 85 the value shown is 2.53E-09

Hope someone can clarify these issues

Steve

  • 0
    TI__Genius 9140 points

    Hi Steve:

    Please see my answer below:

    1] Can you attach the excel calculator you use? I will have a look at it based on your input.

    2] Could you be in more detail, what parts are not the same with TI Schematic?

    3]In the datasheet,TI recommend to set the turn ratio between 50 and 200.

    4]do you mean reset circuit?  there are three kinds of this circuit in datasheet in Page 39 in the datasheet.

    5]Line 85 is in yellow, you should fill in the real value you can find .

    best regards

    wenbin

  • 0 in reply to David Huang33
    Prodigy 80 points

    Dear David,

    Thanks for your prompt reply.

    In looking at the various designs proposed on the TI web site I made a small table for the following:

    Caox has resistor (Rzcb) values from 3K9 to 10K, (Czcb) from0.0033 to 0.01mfd and Cpcb from180pF to 1000pF.

    Rimo sometimes shows a parallel capcitor of about 1000pF

    Rsynth varies from 68K to 215K

    I understand that these various designs have Fosc from 38KHz to 100KHz but you can see on my attached spread sheet that the values in

    YELLOW do not agree with those in GREY and are not even close to the designs on TI site.

    I figured out that the snubber on the sense XFR is best to use a R-C type.

    What is this -1.41E+03 all about?

    Regards

    Steve MantzUCC28070 Zed.xlsx

  • 0 in reply to Stephen Mantz
    TI__Genius 9140 points

    Hi Steve:

    you need to fill in the correct value according to Grey value. Once you changes the input spec, you should get different grey value. Then you can change the yellow item according to the grey.

    for the -1.41e+03, that is because you fill in a too big current sense offset at line 48, Please try to decrease Voff from 0.5 to 0.2.

    thanks.