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LM5072: Change from -50 to -80 version of part...

Soren Steen Christensen
Genius 3685 points
Part Number: LM5072

Hi TI Support,

I have a question with respect to a design using TI part number LM5072MH-50/NOPB for a PoE power supply. Design have been build in the 1K+ quantities with no problems, but now on upcoming build we get information that LM5072MH-50/NOPB part no longer exists, but only LM5072MH-80/NOPB. As design is something I have "inherited" I unfortunately don't know it in every detail so I'm trying to understand if the LM5072MHX-80/NOPB part can directly replace the originally used LM5072MHX-50/NOPB part, or if there is anything I need to pay special attention to during this upgrade?

I have of cause gone through datasheet and I can read that -50 vs -80 relate to maximum PWM converter duty cycle and slope compensation (or not), but what this exactly relate to in "the real world" I'm a bit more unsure, but hope that someone of you guys can easily clarify, as LM5072MHX-50/NOPB no longer seem available (despite datasheet still mentioning it at multiple places)?

Hoping question is clear - Best regards and thanks in advance
  Søren

  • 0
    TI__Genius 9230 points
    Hi Soren,

    To summarize your question:
    1. Can the -80 directly replace -50?What is the difference between -50 & -80?
    2. How does "maximum PWM converter duty cycle & slope compensation" related to in the real world?

    Yes, the this part can be used in the exact same fashion. The slope compensation is an automatic feature that is necessary to keep the system stable above 50% duty cycle. What happens is that a sawtooth voltage is subtracted from the output of the error amplifier to compensate for sub-harmonics that occur at duty cycles above 50%. Now, why would you care to have >50% duty cycle? Well, it allows for a wider range of input voltages for the device. Since your system was designed with the -50, your system was not designed for >50% duty cycle so you're good.

    Thanks,
    Thomas A.
  • 0 in reply to Thomas Amlee
    Genius 3685 points

    Hi Thomas,

    Thank for good and fast reply. Exactly what I needed. :-) It was my assumption as well, but based on the datasheet didn't feel 100% sure so I though to better ask (to be better safe than sorry) in case there could be any small difference I should had paid attention to :-) Thanks for confirming that there isn't and that it's supposed to work out the box with no changes needed :-)

    Best regards and thanks again
      Søren