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LM5022: vs LM3478?

Olli Mannisto
Expert 1750 points
Part Number: LM5022
Other Parts Discussed in Thread: LM3478, LM5155

I have used the LM5022 on a previous design, however with the friendly scalpers in HK purchasing all parts they can, it's in short supply like many other TI SMPS controllers and regulators. 59 weeks factory lead time for TPS54335ADDA? Ouch.

Looking at the selection I've found LM3478 as a potential replacement, it's not pin or function compatible but both can do the same job more or less. Is there a reason to prefer one over the other? LM5022 is somewhat more capable but nothing drastic as far as I can tell:

  • Max Fsw is 1MHz vs 2.2MHz
  • Operating voltage is 3-40V vs 6-60V
  • Mad duty cycle is 100% vs 90%
  • Error amplifier is transimpedance vs regular
  • LM3478 does not support external sync, LM5022 does

None of these really matter for 12Vin 48Vout 0.5A boost converter I'm designing.

LM3478 has better supply situation although scalpers have been purchasing them like they were going out of fashion, with half a million or more in hoarded to China depending on variant. But you can still buy it in normal distributors, at least for now.

  • +1
    TI__Genius 17560 points

    Hi Olli,

    Sorry to hear you've been having sourcing issues. In your application, there does not seem to be a crazy difference assuming it is just 12Vin 48Vout 0.5A boost. One thing to note is that the LM5022 does have adjustable soft-start time and UVLO, which can give you more control over the start-up. Other than that, I think it is fine to use the LM3478 as a potential replacement. 

    If you are also curious, the LM5155 is a next-gen variant of the LM3478 part, which you can find here. The main difference here is that the quiescent current is much smaller with the LM5155 than with the LM3478.  

    Thanks,

    Richard

  • 0 in reply to Richard Fu22
    Expert 1750 points

    Hi,

    Everyone's having sourcing issues. I was just talking to my boss that we should place order for 1-2k pieces of TPS54335ADDA that has some stock becoming available one year from now so we don't have to pay HK scalper prices when our stock exhausts. Going rate for that chip is now $20+, some 20x more than the list price.

    For the same reason LM5155 is a non-starter, it has essentially zero stock, even including scalpers. Plus it's a WSON chip, not very friendly if you have to hand assemble proto circuits.

    I'll (have to) go with LM3478, as a bonus it's got useful appnote AN-1286 https://www.ti.com/lit/pdf/snva067 which together with Sheehan's seminar paper https://www.ti.com/seclit/ml/slup340/slup340.pdf makes it easier to suss out the feedback loop.

    Hopefully the feedback loop tweak functionality in old Webench comes back any year now, that actually "made things easy".