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Original question:

LM5158-Q1: Fast temperature rise

LM5157EVM-SEPIC: 60V Input Modifications

Garrett Schmuelgen
Prodigy 40 points
Part Number: LM5157EVM-SEPIC
Other Parts Discussed in Thread: LM5158

I was trying to use the LM5157EVM-SEPIC board to test the LM5158QRTERQ1 part. I am trying to test with an input range of 17V-60V and output 25V, so I made some modifications to the board, but it failed when I applied 60V.

Here are the parts that I replaced and what I replaced them with

U1 – LM5158QRTERQ1

L1 – SRF1260-220M

D1 – PMEG6030EVPX

C8 – GRM31CC72A475KE11L X2

Input Caps – GRM31CC72A475KE11L X2

C21 – GRM155R62A104KE14D

R6 - ERJ-2RKF4702X

R9 - ERJ-2RKF1961X

Are there any parts that I missed that need to have a higher voltage rating or is there a different problem?

Thanks

Garrett

  • 0
    TI__Genius 16995 points

    Hi Garrett,

    D1 has a stress of more than 85V. Please replace it with a 100V diode.

    Best Regards,

    Feng Ji

  • 0 in reply to Feng Ji
    Prodigy 40 points

    I replaced the diode with PMEG10030ELPX to make it 60V capable. When doing this the board was only able to supply 120mA. When putting a 250mA load on it, the output produced a lot of oscillation and only supplied 120mA. It worked fine with a 120mA load. This was with an input voltage tested at values between 19V and 32V. This is all with my own prototype board, but the parts are the same as above. With the old diode, PMEG6030EVPX, the design works fine up to a 500mA load, and I have not tested any higher yet. 

    Do you see anything in the datasheet that would point to why this failure may be happening? The only difference that I can see is that the 100V capable diode has a slightly higher forward voltage, but I wouldn't think that this would make a difference in this case. 

    Do you have a recommendation for a diode that would work well for my application? We are trying to design for a small solution size so I'd prefer to not use any massive diodes.

    Thanks

    Garrett

  • 0 in reply to Garrett Schmuelgen
    TI__Genius 16995 points

    Hi Garrett,

    I do not think a bit difference in forward voltage would make this difference.

    LM5158 has an 85V MOSFET which seems not enough for your SEPIC application.

    Best Regards,

    Feng Ji