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TPS549B22: About the capacitor value for the BP pin

tsuyoshi tokumoto
Expert 2630 points
Part Number: TPS549B22

Hello team,

  My customer wants to use a 10uF ceramic capacitor between the BP pin
  and DRGND from the viewpoint of easy availability.
  Is it usable?


Sincerely,
Tsuyoshi Tokumoto

  • 0
    TI__Guru**** 191445 points
    Tokumoto-san,
    It is probably ok. Let me double check.
  • 0 in reply to JohnTucker
    TI__Guru**** 191445 points
    Tokumoto-san,

    Actually it is not ok. VREG LDO in TPS549B22 can support a bypass cap as large as 4.7uF. Using a 10uF cap for VREG output can cause LDO’s stability margins to drop, which can show up as load transient settling and oscillation problems.
  • 0 in reply to JohnTucker
    Expert 2630 points

    Hello Tucker-san,

      Thank you very much for your prompt reply and your double check.
       I discussed your advice with my customer this morning.

       Please let me ask you an additional question.

       Could you please tell me the range of values of capacitor which is usable?

       As you know, we have an issue regarding the availability of ceramic capacitors now.
       We will make an effort to obtain the 4.7uF ceramic capacitor preferentially,
       but we want to expand the range of usable capacitor values as much as possible.

       For example, is there any problem with the use of two 2.2uF ceramic capacitors?

       Please lend your expertise.

    Thank you and best regards,
    Tsuyoshi Tokumoto

  • 0 in reply to tsuyoshi tokumoto
    TI__Guru**** 191445 points

    Tokumoto-san,
    For these type pin functions, the circuit is designed for a specific value of capacitance. The device is not characterized for other values. Based on the IC designers comment above, a bypass cap as large as 4.7uF is supported, so I would expect 2 X 2.2 uF would be acceptable. Please check the DC bias rating of the capacitors you intend to use. I would thing 10 V or 16 V rating would have sufficient capacitance at the BP voltage level.

  • 0 in reply to JohnTucker
    Expert 2630 points

    Hello Tucker-san,

      I appreciate your prompt reply and great advice.
      We will design the capacitance value as follows.

       - The first choice
             Using 4.7uF(Rated voltage:10V or 16V) ceramic capacitor

       - The second choice
             Using 2x2.2uF(Rated voltage:10V or 16V) ceramic capacitors

    Thank you and best regards,
    Tsuyoshi Tokumoto