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UCC28740: Could you tell me about how to use UCC28740?

Pokkun
Genius 4695 points
Part Number: UCC28740
Other Parts Discussed in Thread: TL494, TL2842, LM5021, PMP30276

I made a post below.

https://e2e.ti.com/support/power_management/isolated_controllers/f/188/t/662888

Based on this post I proposed UCC 28740 to the customer, but I got additional questions.

I will write down the question items below, so can you teach?

About how to use UCC28740.

①: Although it is described that the frequency always fluctuates depending on the current value of the IFB, is it possible to use the switching frequency fixed at 100 kHz?

②: Can you respond to the following specifications?

　Input: 154 to 480 V @ AC

　Output: 24 V, 0.1 A @ TYP ⇔ 0.5 A. (10 ms / 1s)

　Fsw: Fixed to 100 kHz (tolerance ± 10%)

③: When the protection function was appling, is latch protection type or temporary stop type?

④: What kind of function is "Low-Line" of protection function?

⑤-1: Is the correct my recognition with the following about the power supply startup related to the VDD pin?

　First, start up by supplying VDD using the voltage of the primary side power supply.

　Next, when the secondary side output is made, this voltage is supplied and operated.

⑤-2: Also, based on this operation VDD_on is not recognized if it does not become 21V@TYP more, Is my recognition correct ?

⑥: I felt it severe to respond to the contents of ①~⑤ with UCC28740.

I think that TL494 or TL2842 is good as one that can correspond to this content and can be constructed inexpensively, but is there any other good device?

Best regards,

Pokkun (Masumi Sekiguchi)

  • 0
    TI__Intellectual 880 points
    Hello Masumi-san,

    Thanks for all the questions! I'll answer them in the order you listed them.

    1: Although it is described that the frequency always fluctuates depending on the current value of the IFB, is it possible to use the switching frequency fixed at 100 kHz?

    You are correct, the UCC28740 operates in frequency and amplitude module modes during voltage regulation. You can configure the transformer specs such that at full load the device will operate near the maximum switching frequency (100kHz) or a little bit less to design for tolerance.

    I would recommend taking a look at the LM5021, which has a programmable frequency pin.


    2: Can you respond to the following specifications?

    The UCC28740 can handle the input/output specifications you are looking at. TI has several reference designs for the UCC28740 which have wide VIN ranges. For example the PMP30276 is a 440VAC input with 6W output. The output can be tailored to fit your design specs.

    Since the UCC28740 is not a fixed frequency device, it would not meet that specification. However, the LM5021 would be a good alternative due to the programmable frequency feature.

    3: When the protection function was applying, is latch protection type or temporary stop type?

    The fault protection for the UCC28740 is a reset and restart, or a temporary stop type of fault protection.

    4: What kind of function is "Low-Line" of protection function?

    The UCC28740 monitors the input line bulk voltage through the VS pin and can determine whether or not the input is too low for the device to run, starting an input undervoltage fault protection cycle.

    5-1: Is the correct my recognition with the following about the power supply startup related to the VDD pin?

    Yes you are correct. On initial startup the high-voltage switch is connected to the bulk-capacitor voltage through the high-voltage pin and charges the VDD capacitor. When VDD reached 21-V UVLO turn on then the controller is enabled and will start switching operation.

    5-2: Also, based on this operation VDD_on is not recognized if it does not become 21V@TYP more, Is my recognition correct ?

    During the startup operation, VDD needs to reach 21V@TYP for UVLO turn on. Otherwise the device will not start switching.

    6: I think that TL494 or TL2842 is good as one that can correspond to this content and can be constructed inexpensively, but is there any other good device?

    I recommend taking a look at the LM5021, which will fit your specifications.

    I hope this answers all of your questions!

    Regards,
    Davit
  • 0 in reply to DavitKhudaverdyan
    Genius 4695 points
    Hi, Davit-san.
    Thanks for the reply.
    Please teach me the following.

    〇About 1 & 2's answer.
    I was understood that LM5021 is better than UCC28740 on this specification.

    But my customer want to use as cheap a device as possible.

    So, I recognized your answer is UCC28740 can be used at fixed frequency by devising transformer design.
    Therefore, if there are no points that can not be used fatally I try to give UCC28740's EVM and samples.

    ・For example, how do you design a transformer design?
    ・Is there anything points that can not be used fatally?

    Best regards,
    Pokkun
  • 0 in reply to Pokkun
    TI__Intellectual 880 points
    Hi Pokkun-san,

    So I want to clarify something. You can design the UCC28740 so that at -full load- the device will be operating near 100kHz, but because UCC28740 has AM/FM modulation at lower loads the converter will switch at a lower frequency.

    In other words, the UCC28740 is not fixed frequency for all load ranges.

    If you still choose to design with the UCC28740, here is a design calculator that you can use to help get you started: www.ti.com/.../sluc487

    How cheap of a device is the customer looking for? What does "as cheap as possible" for the customer mean?

    Regards,
    Davit
  • 0 in reply to DavitKhudaverdyan
    Genius 4695 points
    Davit-san.
    Thank you for the answer!

    >How cheap of a device is the customer looking for? What does "as cheap as >possible" for the customer mean?

    ⇒I am looking for a controller that is less than about $0.18.
    　The customer said,about below ¥20 Japanese yen is the target price.
  • 0 in reply to Pokkun
    TI__Intellectual 880 points

    Hello Pokkun-san,

    Thanks for the info.

    For more questions and information about pricing please reach out to your local TI representative so that they can answer your questions in an appropriate channel.

    Regards,

      Davit

  • 0 in reply to DavitKhudaverdyan
    Genius 4695 points
    Hi, Davit-san.
    Thank you for various correspondence!

    I confirmed the latest situation to the customer.
    If the maximum frequency is 120 kHz or less, the customer says even if the frequency fluctuates depending on load, it can be used.

    For that reason, you responded that they can be used in terms of power supply voltage and output power, so I will proceed with the proposal at UCC28740.