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PTN78000A: Nonceramic Input Capacitor

Charles Gervasi
Expert 2270 points
Part Number: PTN78000A
Other Parts Discussed in Thread: LMZ34002,

The PTN78000A datasheet says on page 10 that "100uF of nonceramic capacitance is required on the input bus." 

Is there any reason all the input capacitance cannot be ceramic?  

Ceramics have become amazingly small.  I can get 100uF at 16V in a 1210 package.  Disadvantage are capacitance decay over time, capacitance decreasing with DC voltage, and piezoelectric noise.  Electrolytics certainly have their disadvantages: packages not smaller than ceramics, shorter lifetime, need to specify low ESR and calculate heating due to ripple current and factor that into component life.  

  • 0
    TI__Mastermind 19891 points
    Hello Charles,
    Let me confirm with the folks who designed this module. I am hoping to get back to you sometime tomorrow.
    Cheers,
    Denislav
  • 0 in reply to Denislav Petkov
    Expert 2270 points

    Denislav Petkov said:
    Let me confirm with the folks who designed this module.

    Thanks for seeking out the people who know the answer and detailed reason.  

  • 0 in reply to Charles Gervasi
    TI__Mastermind 19891 points
    Hello Charles,

    These modules are probably 15 years old and at the time there were probably no high value ceramic capacitors with the proper rating. The ceramic capacitors should work OK, just be sure to consider the capacitance de-rating under voltage bias.

    Question: Have you considered newer modules like the LMZ34002?
    Here is the datasheet for that part: www.ti.com/.../lmz34002.pdf

    Cheers,
    Denislav
  • 0 in reply to Denislav Petkov
    Expert 2270 points

    Denislav Petkov said:
    These modules are probably 15 years old and at the time there were probably no high value ceramic capacitors with the proper rating. The ceramic capacitors should work OK, just be sure to consider the capacitance de-rating under voltage bias.

    Question: Have you considered newer modules like the LMZ34002?

    I considered LMZ34002 but decided against it b/c it would be harder to solder and real estate is no a big issue for me.

    I am now reconsidering it.  Do you suspect it has a longer product life-cycle ahead of it before EoL than PTN78000A?  

    Added Feb 12: I'm marking this as Resolved, but it would still be useful if you could point me to product lifecycle info.