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LM5180: Surge Immunity Compliance of LM5180

Avik Bhowmik
Prodigy 90 points
Part Number: LM5180
Other Parts Discussed in Thread: , LM25180, LM5161, LM5017
Hi
We are testing EMI/EMC compliance testing of our product which is based on LM5180 converter IC.
We are facing issues in the Surge Immunity Test (IEC 61000-4-5) as the LM5180 IC is getting damaged during test.
The Surge Voltage level applied was +500V and pulse waveform was 1.2/50uS.
The required compliance level is +/- 1000V but failure occurs at 500V itself.
The operating range of the power supply design is 10-60VDC. The design is same as the LM5180EVM-DUAL schematic.
Right now we have used a MOV (60 Vrms rated) in parallel to the Aux Input terminals for protection, but the IC is still not protected.
What is the recommended protection circuitry for this IC for Surge Immunity?
Thanks
Avik
  • 0
    TI__Expert 8130 points

    Hello Avik,

    I will check with the team internally and see if we have any available data on this.

    Regards,
    Alejandro

  • 0
    TI__Guru 74052 points

    Hi Avik,

    One option is to choose an appropriate TVS to clamp the incoming transient voltage event. The abs max on VIN is 70V. Given that Vin-max is 60V here, there isn't much margin. However, you can also include a damped LC input filter to attenuate the incoming transient.

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    Prodigy 90 points

    Hi Tim

    The 10V margin is the main reason for concern. All the shunt types of clamping devices like TVS, MOVs, etc have a much higher breakdown margin. If I select a device with a clamping voltage of around 70V, then it will interfere within the normal operating range itself i.e. before 60V. But, still for trials I tried using an SMBJ TVS diode to see where it actually clamps the transient voltage and the TVS itself got blown!

    I have played around with several values of inductors and there are two issues I came across-

    1. The inductor seems to damp the transient but then the lower point of my power supply gets shifted and that I can't do. Since the required power supply range is 12-60VDC, I need it to start from at least 11V and lower the better. Because of the additional drop across the inductor the starting point gets shifted to greater than 12V.

    2. After selecting an appropriate value of inductor (approx. 500mH) considering the above tradeoff, the clamped voltage reaching Vin is around 80-85V which is still dangerous for the IC.

    Please share your thoughts on how to counter these points or any other clamping mechanism we can work with.

    Thanks,

    Avik

  • 0 in reply to iAlejandro
    Prodigy 90 points

    Hi Alejandro

    Any Surge / Transient compliance-related data for LM5180 or any other similar part would be very helpful.

    Also, you must have done internal EMI/EMC testing for these parts. Please share some related schematic or design inputs so that I can implement the same.

    Thanks,

    Avik

  • 0 in reply to Avik Bhowmik
    TI__Guru 74052 points

    Hi Avik,

    Please consult the TI Designs for the LM5180/-Q1 and LM25180/-Q1 provided in the respective product folders. Also, EMI results are available in the datasheets and EVM user's guides.

    Given that Vin-max of the application is 60V and you need to clamp prior to 70V, a TVS may not work as its clamping voltage for the surge current level is well above its standoff voltage. An input LC filter would attenuate the surge waveform, something like 10uH and 100uF (500mH above sounds excessive). This should not affect input UVLO as the DC drop across the input inductor is minimal.

    Another option to consider is our 100V Fly-Buck converters such as the LM5161 (100V/1A) and LM5017 (100V/0.7A). This gives increased Vin margin to manage incoming transients.

    Regards,

    Tim