• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 64 subscribers
  • Views 4073 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.

what is the difference between bypass and decoupling capacitors ? how to size bypass capacitor for analog cicuitry ?

anindya bhattacharyya
Prodigy 90 points

the capacitors generally attached to the power supply pin of the opamps are decoupling capacitors or bypass capacitors or are they the same thing and the terms  can be used interchangeably? how to size them and does psrr play a part in choosing the bypass/decoupling component ? if the value of the capacitance to be added is not mentioned in the datasheet and the opamp  is getting power from a dual output dc to dc converter +/-15v having an output ripple of 120 mv and a switching frequency of 170 KHz ? it would be helpful if someone can throw some light on the design basis of output filter of dc to dc converter to reduce the ripple ?

                                     thanks in advance

  • 0
    TI__Mastermind 25130 points

    Anindya,

    The two terms are used interchangably. Usually for op-amps people will put  a 0.i uF cap across the power to ground rails. For a power converter it is a little more tricky because you have to realize that the power converter will; be pulling the gate charge for the FETs that it is powering from the bypass capacitor (very high di/dt) and it also needs bulk capacitance to allow for startup requirements so often you will see several microfarad capacitor capacitor along witha 1 uF ceramic across the power pins of a converter. The attached article deals with the start up capacitance requirements of a power converter.

    http://ednasia.com/article-7993-inputcapacitorconsiderations-Asia.html

    Hope this helps.

    Regards,

    John