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UCC28910: how to choose Input Line filter parameters and its effect

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Part Number: UCC28910

Hi Team,

There is no explanation  about how to choose L1, L2, R1, and R2 parameter for effective EMI reduction as input AC line filter in the datasheet
(I can understand that those components are used for AC line filtering for EMI reduction from following description in the UCC28910's datasheet )

10.2.1.2.2 Input Stage Design and Bulk Capacitance
4. A line filter (L1, L2, R1, and R2) to reduce EMI generated by switching.

Could you tell me how to choose those parameters properly?
Do you have any app note about the input line filter setting? If yes, please let me know the document number.

I'm also curious what kind of side effects will come out if we don't put the line filter in there since those components are big size and take non-negligible costs.
Could you tell me what kind of case we can remove the filter in the system using UCC28910?(ex, PMP9171)

Regards,

Takashi Onawa

  • Takashi-san

    L1, L2, R1, and R2 are part of the input EMI filter, which enables compliance with required standards such as CISPR 32/EN 55032. The EMI filter is highly dependent on parasitic component effects of the design, such as PCB layout and transformer construction. As a result it is recommended to measure the EMI performance and modify the design as needed to pass.

    Below are some documents that go into more detail on EMI filter design and show different ways to design the filter.

    Overview of EMI standards: www.ti.com/.../slyy136.pdf

    EMI Introduction: training.ti.com/introduction-emi-power-supply-designs-sources-measurements-and-mitigation-methods

    Flyback transformer design considerations of efficiency and EMI
    Paper: www.ti.com/.../slup338.pdf
    Presentation slides: www.ti.com/.../slup339.pdf
    Presentation video: training.ti.com/flyback-transformer-design-considerations-efficiency-and-emi

    Best Regards,
    Eric
  • In reply to Eric Faraci:

    Hi Eric-san,

    OK, I understood that L1, L2, R1, and R2 are part of the input EMI filter and those component might be needed to pass strict EMI exam.

    Could you tell me where we can find how to choose the parameter in the documents?
    I didn't find the discription in the documents, so please let me know where is it.

    Also, Are these components optional? Or we much put them there? 

    In douments below, I found the following sentence and it says those componenets are for ESD protection and to prevent input oscillations. So, I could not judge whether it is mast or arbitrary.

    www.ti.com/.../sluuba1.pdf

    R1, R2 serve the dual function of dampening input filter oscillations and prevent a large voltage being developed across L2 and L3 in the event of an ESD pulse.

    Regards,

    Takashi Onawa

  • In reply to Takashi Onawa:

    Takashi-san

    You are correct about R1 and R2, these specific devices work to reduce the Q for the LC resonant tank of L1, L2, C1 and C2. The ESD pulse is an additional feature they provide. During high transient like an ESD event, the L has a very high impedance so R1 and R2 act as a series resistance to dissipate the energy. If L1 and L2 were not in the circuit another device, like a MOV or TVS diode, could be used to suppress the energy. You need to determine what is required and how to implement it. Surge or ESD event is system level spec that varies between applications and often times has regulatory requirements.

    The UCC28910 datasheet does not explain how to design the EMI filter. Unlike other components in the design, EMI filter design is dependent on non-ideal parameters (such as transformer construction and PCB layout) so it's not as simple to design like other system components. If you follow the the training collateral in my first message you can learn about how noise is generated and common techniques used to filter them. There are multiple ways you can design EMI filters, so I recommend you review all the collateral and identify which way would work best for you.

    Best Regards,
    Eric

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