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PTH08T240W Stability question

carl armstrong
Prodigy 20 points
Other Parts Discussed in Thread: PTH08T240W

Hello,

I have a design that requires 20 SFP optical transceivers (3.3V). The recommended power circuit requires 2 10uf caps per SFP module. That would be

40 10uf caps. Using ceramics with an ESR of 2milliohm would give an equivalent ESR of 1/40... 50picoohms!! Correct??. I'm targeting the PTH08T240W

12v in 3.3v out powering also the io of 4 fpgas, 12 sdram chips and misc for a load of 8A max(no transient response issues in the design).  The datasheet specs

non-turbo trans max 0f 500uf ceramic and a min of 7milliohm of non-ceramic ESR.  of Will this configuration be stable with a 220uf poly-tant(18mohm ESR) on the output

of the module? If not, any suggestions?

Regards,

Carl

  • 0
    TI__Mastermind 38230 points

    The   PTH08T240W requires at least one  220µF polarized capacitor on the output bus. The 18mΩ 220µF is fine  when using the 400µF ceramics( 40 x10µF) The only requirement  is maximum ceramic capacitors limit is 500µF. ESR  is not a factor when using ceramic capacitors. The turbo trans function cannot be used with the PTH08T240W.

    There is a module, PTH08T241 which requires only  ceramic capacitors , located in the PTH08T24X product specification .  It only requires all ceramic capacitors on the  Vout bus. The only other requirement is the minimum output ceramic capacitance is 300µF and maximum capacitance is 3000µF.  Input capacitor can be polarized or ceramic type capacitance .

    Tom