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LM5017 Power up Issue

Andrew Meikle
Prodigy 90 points
Other Parts Discussed in Thread: LM5017

I have designed a product using the LM5017.

When I powered up the second unit I assembled, It worked fine at 30v. I then powered it up at just under 80v, and the input leg (VIN) on the LM5017 vaporised.

I have a 2.2 uf and a 100nf capacitor on the incoming power rail.

I tried My third sample and it also blew the LM5017 VIN pin.

I then added a 10uf capacitor to the incoming rail of my forth and fith sample and it works fine.

In the documentation It said that a 2.2uf is ok for the incoming supply.

What is going on, why did the 2 samples blow.

I don’t want to start production on this product if there is some issue with the LM5017

Andrew

 

 

  • 0
    TI__Genius 11490 points

    Hi Andrew,

    What application are you using it in? I will need some more information about the experimental setup, e.g., power supply, wiring etc. Depending on the power supply, slew rate, wire inductance, and capacitances at the output of power supply and at the input of converter, turning on the input power supply results in higher VIN spikes at the input of the converter. Were you able to capture the input voltage waveform during power up. That will clearly show if the voltage at the VIN pin exceeded 100V.

    Regards,

    Vijay

  • 0 in reply to Vijay86929
    Prodigy 90 points

    Hi Vijay

    Thanks for getting back to me.

    It is powered by batteries, so there is no serge from that side.

    I do think that it was caused by a spike that the LM5017 may have created during its boot sequence.

    I was thinking about adding a 100v zener diode from the supply rail to ground, to clamp out any spikes above 100v. A 99v zener would be ideal, as it would clamp the spike prior to reaching 100v. But I only saw 91v and 100v from my supplyer.

    I haven’t had a chance to check if there is still a spike present with the 10uf capacitor. But I will check and get back to you on that.

    Andrew

  • 0 in reply to Andrew Meikle
    Prodigy 50 points

    Hi Meikle,

    Did you find out what the problem was.  I'm having similar problems here.  It appears to me the evaluation design cant handle transients?

    Regards

  • 0 in reply to paul wilkinson
    Prodigy 90 points

    Yes I did resolve the Issue.

    You need to increase the size of the capacitor on the incoming voltage supply.  

    I used a 2 separate capacitors, a 2.2uf 100v and 10UF 100v electrolytic due to restricted space.

    If you can use a 22UF or larger, that should resolve your issues. 

    Note: It must be connected directly between VIN and RTN pins on the IC (see below)

    supply + [Diode>]  [22uf +] [VIN on IC] 

    Supply -                [22uf - ] [RTN on IC]

     

    Regards

    Andrew

  • 0 in reply to Andrew Meikle
    Prodigy 50 points

    Thanks for the prompt response.

    TI have asked to have the board back for analysis.  In the mean time I have ordered another board and will try what you suggested.

    Thanks again!