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  • TI Thinks Resolved

UCC28780: It seems that a disturber came in

Expert 2765 points

Replies: 9

Views: 141

Part Number: UCC28780

Hi, All

But I want the opinion of a transformer expert.

A TI's competitor flyback maker seem to be bringing in a large transformer, saying that QR Flyback alone can deliver 93% efficiency @ 27 W for less understood customers.

But that customer want to make small adapter like 30W GaN Anker.

I want to talk to the customer, "With a small transformer such as the size of a 30W GaN USB PD adapter Anker, an efficiency of 93% can not be achieved with a simple QR Flyback IC."

Does someone have the data such as Transformer size vs efficiency at QR Flyback?

  • Hiroshi-san

    You are correct, in order to achieve small solution size and have high efficiency an active clamp flyback will have to be used instead of a QR flyback.

    The size of the adapter is dependent on the switching frequency.  To achieve small solution size the frequency needs to be increased as high as possible.  The following app note, technical training video and TI Power Supply Design Seminar (PSDS) presentation describe how the active clamp flyback is able to reduce losses compared to a QR flyback, allowing it to operate at higher frequencies (which means smaller size) than a QR flyback

    App Note: http://www.ti.com/lit/an/slua871/slua871.pdf

    Training Video Part 1: https://training.ti.com/active-clamp-flyback-part-1?cu=1134585

    Training Video Part 2: https://training.ti.com/active-clamp-flyback-part-2?cu=1134585

    PSDS Paper: http://www.ti.com/lit/slup380

    PSDS Presentation Slides: http://www.ti.com/lit/slup381 

    PSDS Video: https://training.ti.com/psds2018#section-3 

    For a design comparison below are 3 designs that have similar specifications that you can use to compare what the differences are.

    QR Flyback: http://www.ti.com/tool/PMP11451

    ACF with Si FET: http://www.ti.com/tool/PMP21479

    ACF with GaN FET:  http://www.ti.com/tool/TIDA-01622

    Best Regards,

    Eric

  • In reply to Eric Faraci:

    Eric-san,

    Your point of view, TI ACF frequency is higher.

    Everybody knows high frequency reduce inductance.

    But the customer is focusing 27W.

    TI reference design is higher wattage such as 45W and  65W.

    I would like to know at what frequency the already proven compact 94% 27W or 30W ACF GaN adapter is operating.

    And can you say that that 27W or 30W adapter transformer size is kept small by the high frequency?

  • In reply to Hiroshi Doi35:

    Hiroshi-san

    We can't comment on specifics of any design that a customer uses with our products.  If you find or perform a tear down on a product yourself you'll be able to answer your question.

    Best Regards,

    Eric

  • In reply to Eric Faraci:

    Eric-san,

    We have no budget to buy a 30W GaN USB PD Adapter.

    So I will give up to recommend UCC28780 to big volume Japan 27W USB PD Adapter maker.

    I think one QR Flyback competitor is now making 27W 94% efficiency board units, same size as UCC28780EVM-002. It is easy.

    But we cannot show the customer smaller one using smaller 27W ACF transformer.

    Thank you.

  • In reply to Hiroshi Doi35:

    Hi all,

    Some IC makers seem to be releasing ACF GaN controller samples by the end of the year.

  • In reply to Hiroshi Doi35:

    Hiroshi-san

    You don't need to wait, our UCC28780 works with GaN and is available today.  We have the following 45W EVM http://www.ti.com/tool/ucc28780evm-002, 65W reference design http://www.ti.com/tool/TIDA-01622 and 100W reference design http://www.ti.com/tool/TIDA-01623 that all work with GaN.

    Best Regards,

    Eric

  • In reply to Eric Faraci:

    Eric-san

    The 45W reference design is not useful for 27W transformer sizing. Is there no transformer professional at TI anymore?

    Your 65W GaN reference design comment below # two page is,

    http://www.tij.co.jp/jp/lit/ug/jaju496b/jaju496b.pdf

    "This converter operates at a high switching frequency of 600 kHz (max), which helps decrease the size of the transformer and capacitors."

    But it locks like 250kHz waveform at heavy load.

    250kHz heavy load and 600kHz light load
    Which of these determines the size of the transformer?
    Can TI offer size selection formulas?

  • In reply to Hiroshi Doi35:

    Hiroshi-san

    The minimum frequency, which is the operating point at full load, determines what the transformer and bulk capacitor size is.  The reference design TIDA-01622 you provided a link does not operate at the highest frequency UCC28780 can support.  It has a lower frequency to balance between cost and efficiency.

    The highest minimum frequency we recommend to design for is 600 kHz, since the frequency will increase up to the maximum 1 MHz operation over the entire operating range.  We recommend to use planar magnetics for the transformer in such a design.  We currently do not have a reference design that demonstrates this.

    To help with your own design you can use our SIMPLIS model http://www.ti.com/lit/zip/slum626 and Excel Calculator http://www.ti.com/lit/zip/sluc664, which include calculations for key parameters for the transformer. With this information you will be able to work with your preferred magnetics vendor to build the transformer. 

    Best Regards,

    Eric

  • In reply to Eric Faraci:

    Eric-san,

    Many customers can not to use them because they can not visualize design specifications unless a calculation formula embedded in an Excel cell is disclosed. 

    Japanese many customers are going to evaluate another control IC.

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