• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 64 subscribers
  • Views 437 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM2594HV: LM2594 input capacitor selection

David Wallén
Prodigy 30 points
Part Number: LM2594HV
Other Parts Discussed in Thread: LM2594

Hi Texas Instruments,

I am designing a step-down power management circuit for 48V that should output 5V using LM2594HV.

I am having a problem selecting the input capacitor for the circuit, the datasheet suggests to use a Tantalum capacitor or Aluminium electrolytic with a voltage rating of 1.25 times the input voltage.

The input of 48V doesn't really make tantalum a choice, since all Tantalum caps with 60V (40*1.25=60) costs 50 EUR or more, and it is not in my budget for this board.

The Aluminium electrolytic caps I am finding with 60V rating seem to have quite large footprints (in the range of 3-6 times the size of the LM2594HV footprint), and this ideally does not work on my intended layout either.

When looking at the layout example in the datasheet it is seems that the footprint for the capacitor  you have chosen is quite small (in the same size at LM2594). Did you by any chance use a ceramic capacitor here? If so, why have you done that when you recommend tantalum? What would I be trading off if I choose to use a Ceramic capacitor instead? (Ceramics can easily be found with 100V rating with a small footprint).

What would you suggest me to use if I want to keep to about the same size as the layout example?

Thanks in advance!

  • 0
    TI__Guru**** 191445 points
    Good morning User,
    The layout guideline clearly states the input capacitor is a 10 uF, 35V solid Tantalum , AVX TPS series, not a ceramic type.
  • 0 in reply to JohnTucker
    Prodigy 30 points
    Good morning John,

    Thank you for the swift reply. Yes, you are correct, sorry I missed that. I assume that choice would be fine for input voltages below 28 V then.

    But what would you suggest to use if I want to run an input voltage of 48 V? I.e. requiring a 60V input cap.

    Thanks in advance!
  • 0 in reply to David Wallén
    TI__Guru 62845 points
    This device should be OK with a ceramic input capacitor. However, if the input supply
    has any inductance, this low ESR type of capacitor can cause ringing and over-voltage at the input
    when the input supply is switched-on. This can be cured with an Al. type capacitor to add damping. But then you are back to your
    original problem.
    So, I would try it with a ceramic input cap and test in your environment very carefully to make sure there are
    no issues with over-voltage on the input.