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TPS62147: Case of Large output capacitance.

Motoyasu Hattori
Genius 9975 points
Part Number: TPS62147


Hi,

My customer is designing the following:

  • Device : TPS62147 @ 1.25MHz SW-Freq
  • Inductor : 2.2uH
  • Input Voltage : 5V
  • Output Voltage / Current : 1.0V @ 0.9A
  • Output capacitance : C1:44uF near inductor and C2:491uF(total) for next ICs.

On the above case of short distance between C1 and C2, total is 535uF.  On this case, could you please let us know any issues?

If the above case has any issues, do they resolve this issue to add ferrite bead between C1 and C2?   Please advise us.

Thanks and best regards,
M.HATTORI.

  • 0
    TI__Mastermind 25220 points

    Hi Hattori-san,

    Yes, that much ceramic capacitance directly at the output of TPS62147 could cause instability. Some options which will work are to use high ESR caps on the C2, or have a long enough trace from TPS62147 output to the C2 location and have that trace resistance be atleast 10mohm or you can also use ferrite bead since it will introduce a DCR. You need to pick an option and try on your custom board. The basic idea is to dampen the LC double pole Q-factor by introducing ESR or trace resistance or DCR.

    Thanks,
    Amod