Opa 2227/2228/p/pa question

Discussion in 'General Electronics Chat' started by Bipolar, Jul 7, 2011.

  1. Bipolar

    Thread Starter New Member

    Nov 8, 2009
    Hi All,

    I am considering using an OPA2228 op. as a unity gain input buffer/driver in a summing amp as a virtual earth mixer, but understand these chips should only be used at a min.gain of x 4-5. as they are unstable below this point & hence will oscillate!

    Q; would putting a low pF cap across the feedback loop solve this problem? What value should this be then? Is there any other workabout to make it stable?

    I then found out that OPA2227 is a more suitable chip for my purpose, but I've already bought the opa2228!...haste is waste!

    What are the differences between OPA2227/8 with suffixes P/PA in their characteristics. Couldn't find much info Can someone throw some light on this please.

  2. Audioguru


    Dec 20, 2007
    All opamps have a "frequency compensation capacitor" inside. Most are stable when their gain is set to 1. Some have a smaller capacitor inside so that their high frequency response is better but they are not stable at low gains.

    adding a capacitor axcross the feedback resistor makes the gain at high frequencies 1 and will cause some opamps to oscillate and will not fix the oscillation of a de-compensated opamp.
  3. praondevou

    AAC Fanatic!

    Jul 9, 2011
    P is for PDIP, I think.
    The "A" type has a bigger input offset voltage, see specs.