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LM5180EVM-S05: LM5180EVM rework to application of 12Vin to 24Vout not able to regulate

San Lee Khor
Prodigy 40 points
Part Number: LM5180EVM-S05
Other Parts Discussed in Thread: LM5180

Hi,

I was trying to rework the LM5180-Q1Single-OutputEVM board to produce 24V output.

Below are the parameter that we get from the PSR Flyback design tool:

We reworked the EVM board as below;

  • Removed the output zener diode.
  • Change the Cout to 10uF 50V.
  • RFB changed to 121K.

We believe we change all the necessary rework, but we are not able to get the voltage regulated (see ~31V unload and the volage will go low when we enable the E load expected to be loaded with only 1-5mA).

When we increase the Vin to 16.5V then we get the Vout to be 24.8V bit still not able to be load.

Any idea what will be the issue here? 

Thanks,

San Lee

  • 0
    TI__Guru 72565 points

    Hi San,

    It should work for this transformer was verified on EVM.   Which Cout of the EVM do you change to 10uF 50V?  There are C6, C7 and C11 on the PCB. Also, you need to change the output diode D4 to a higher voltage rated device.  In this case, I would suggest a 100V diode.

    Thanks,

    Youhao

  • 0 in reply to Youhao Xi
    Prodigy 40 points

    Thanks Youhao for your confirmation.

    We Changed C6 as from 100uF 6.3V to 10uF 50V. C11 is still remain open and C7 is kept at 0.1uF 25V.

    When you said the output diode, D4 are you meant to be the rectifying diode D2 or the Reset diode D4?

  • 0 in reply to San Lee Khor
    TI__Guru 72565 points

    I meant D2.  Sorry for not being explicit.  

  • 0 in reply to Youhao Xi
    TI__Guru 72565 points

    Hi San Lee,

    Seeing no further comments from you for more than a week, may I assume the issue is resolved so I can close the thread here?  You are welcome to re-open it by adding a new post.

    Thanks,

    Youhao

  • 0 in reply to Youhao Xi
    Prodigy 40 points

    Hi You Hao,

    Are the Transformer trimmed to be operate with Vin >18V? 

    We got a weird waveforms. The Vin is set at 12V. (Chanel 1 is SW and Chanel 2 is Input Current)

    With no load.

    With 5mA

    With 50mA

    With 0.1A

    The Internal MOSFET was not fully turn on? Why it was not pulled to 0V?

  • 0 in reply to San Lee Khor
    TI__Guru 72565 points

    Since you are playing with our EVM by changing parts on it, could you show me a markup schematic with your latest part values or part numbers?   Please make sure the values or part numbers accurate.

    Thanks,

    Youhao

  • 0 in reply to Youhao Xi
    Prodigy 40 points

    Here is the markup on the EVM.

    Highlighted in RED.

  • 0 in reply to San Lee Khor
    TI__Guru 72565 points

    Thank you San Lee.  The schematic looks fine, and it should work.  Sorry to ask, but could you double check your D2 polarity? 

    By the way, could you also take a photo picture of the board?  I wish to read the components.

    Best Regards,

    Youhao

  • 0 in reply to Youhao Xi
    Prodigy 40 points

    Thanks for the confirmation. based on the waveforms shared, do they looked normal to you? Aside, when we load the output at max of 0.15A, the Iin stay  constant at 0.57A?

    We are also seeing the similar waveform with the default condition on the EVM board. Which is diffent from what being share in the datasheet.

    Can you advice where the waveform should we plot. 

    We were plotting the waveform on the test point  between Tp2 & Tp4.

    We are mocking up another EVM to to make sure the consistency. Will share the pic of the board soon.

    Aside, what is the expected Vout  tolerance range? Any way to improve the tolerance? with 10%?

    Based on the understanding, the Transformer that we are using was tested with LM5180. Do you have the test data or any information about the verification with the transformer that we are using??

  • 0 in reply to San Lee Khor
    TI__Guru 72565 points

    If you see the similar waveform before you make the changes, that means the EVM's circuit has already been damaged somehow.  The two datasheet waveforms that you referred to are real and accurate.

    Before you mocking the other EVM, please try to duplicated these datasheet typical waveforms first to make sure the EVM is good. 

    Regarding the transformer, I don't have the test data because the original engineer doing that is not available, but Coilcraft only release the part after verification with the IC.

    Thanks,

    Youhao