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LMR38020: LMR38020 surge test failed

Norbert Nestler
Intellectual 340 points
Part Number: LMR38020
Other Parts Discussed in Thread: LM5085, , STRIKE, LM5168, LM5164

Tool/software:

Hello,

i did a new design with LMR38020 in replacement for the LM5085.

The new design works fine!

But now customer did an emc surge test and LMR38020 died. They told us, that transients with 120V have been measured at the ic.

Do you know, how to improve filter to withstand emc surge test EN61000?

7065.19V-60V-V02.pdf

19V-60V-V02-lay.pdf

  • 0
    TI__Mastermind 26360 points

    Hi Norbert,

    Sorry to hear the design failed. 

    Can you provide the operating conditions, and what methods you may have tried to improve performance, as well as startup waveforms of the VIN, VOUT, and SW?

    I would first suggest incrementally increasing the input capacitance to see if that may help.

    If that does not work, it looks like you may also increase the surge rating of your TVS at the input. It looks like it is rated to only 70V? 

    Let me know how those work out. 

    Thanks,

    Richard

  • 0 in reply to Richard Fu22
    Intellectual 340 points

    Hi Richard,

    thank you for reply.

    The circuit without emc testing works well, it passed also the emission tests.

    The board should have the highest possible immunity against lightning strike.

    The surge pulse (simulation of lightning strike) is applied at max. Vin (60V DC). This makes a 120V transient on the LMR38020 - IC died.

    The recommendation of the tester was, to find an IC with bigger Vin (e.g. 150V). Do you know such a part?

    (Vin 19V to 60V, Vout 15V 1A). The other way should be to improve the input filter.... Is there TI knowhow for lightning input filter?

    Kind regards

    Norbert

  • 0 in reply to Norbert Nestler
    TI__Guru* 76525 points

    Hi Norbert,

    Sorry for the delay, because Richard is out of office and I just found your post today.  Our product line have 120V rated devices like the LM5168/9, but not yet 150V devices. Is 120V rating enough?  

    Thanks,

    Youhao

  • 0 in reply to Youhao Xi
    Intellectual 340 points

    Hi Youhao Xi,

    thank you for your reply.

    120V rating would be great!

    But i need a output current of min. 700mA at 14,5V Vout

    Regards

    Norbert

  • 0 in reply to Norbert Nestler
    TI__Mastermind 26360 points

    Hi Norbert,

    Unfortunately, we may not have any converters that can support such a high-voltage test. If you can clamp down to 100-V, you may also try the LM5164, which is 100-V rated, 1A output. 

    If that doesn't suit your application, you may try the UCC controllers.

    Thanks,

    Richard