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WEBENCH® Tools/LM5176: Anyone succeeded building working ± 43V 10A output?

Ce Jacobs
Prodigy 250 points
Part Number: LM5176

Tool/software: WEBENCH® Design Tools

Having difficulty getting the LM5176 WeBench design to run stable (M1 and Cin near M1 get shorted)
and having the 48V output Linear LTC3779 without any issue on the same load
and only seeing a 12V DC output at the LM5176EVM-HP evaluation board,

I started wondering:

Did anyone succeeded in building a working LM5176 buck-boost switcher that outputs around 43V DC 10A with non resistive loads?

  • 0
    TI__Guru* 78380 points
    No. Our max power ref design is 300W. 430W appear to be a stretch for the LM5176. Recommend to use dual phase.
  • 0 in reply to Youhao Xi
    TI__Mastermind 21720 points
    Hi Ce Jacobs,

    For multi-phase operation using the LM5176 please refer to these two application notes
    www.ti.com/.../snva792
    www.ti.com/.../snva794

    As Youhao mentioned the practical maximum power for the LM5176 is around 300W. Adding a second phase will allow high output power.

    Please let me know if you have an questions.

    Thanks,

    Garrett
  • 0 in reply to Youhao Xi
    Prodigy 250 points
    snva794 states: One single LM5176 converter can deliver power greater than 200 W because of its synchronous switching topology; however, at a higher power, the increased switching and conduction losses can eventually overwhelm a single converter due to excessive board heating. This overheating makes it necessary to parallel power stages to distribute heat.

    In the 300W output range the efficiency was over 98.5% (@most inefficient 33V input) and still increasing when increasing the load. Resulting in a maximum of 1.5% of 300W = 4.5W of heat. In the 4Oz test board I could not find a component that even became hand warm at this load.

    The 300W max power ref design statement also doesn't match WeBench output. WeBench even generates a solution for 10.5A at 45V output (473W) and states a total power dissipation of 3.22 watts.
  • 0 in reply to Garrett Roecker
    Prodigy 250 points

    Our LM5176 prototype definitely doesn't fail because of a heat problem: such a heat can't develop within 5-10 seconds of usage with our 220W nominal 645W peak load. Where the LTC3779 can be used for over 15 minutes with the same load that causes the LM5176 proto boards to fail. The average load is expected to be in the 150-180 watts range.

    I can identify 4 possible sources of failure for our 2 protypes that both failed:
    1. WeBench design is faulty -> [a] component selection or [b] altium file generation [TI]
    2. LM5176 IC is just faulty by design [TI]
    3. PCB design change fault(s) from WeBench Altium design source files [our]
    4. Component substitution: 4 out of 6 ELCO's were replaced with 12 MLCC's (too little resonance damping) [our]
    5. other, ...

    Would you like to attach a percentage to each source, how likely it is that that reason will be the cause for our LM5176 prototypes to short at M1 and Cin near M1 and U1?

    PS For possible cause #3 I have attached the Extended Gerber files.

    BuckBooster_GerberX2_V0.10.zip