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OPA1602: Clipping when used as buffer G=1

Robert Schulte
Prodigy 30 points
Part Number: OPA1602

I used the tidu035crossover as a starting point and then modified the design to build a single low pass filter with the signal path as follows:  I started with the same unity gain buffer stage and 10k input resistance, then two Sallen-Key filters (2nd order Butterworth alignment @ 300Hz)  followed by a unity gain buffer stage.  The unity gain stage is direct coupled from the filter stage.  Input is 1V P-P 20Hz and the power supply is +/-12V.

The output is clipping and refuses to go below zero volts on two out of four of these circuits that were built.  The other two work fine.  I tried adding a 1k resistor to feed the buffer but I still get clipping.

The problem is in the buffer stage... what is going on here?

Thanks for you help!

Bob  

  • 0
    TI__Genius 10850 points

    Hi Bob,

    Thank you for your post. Do you have this circuit built in TINA Spice that you can share with me? 

    -Tamara

  • 0 in reply to Tamara M Alani
    Prodigy 30 points

    I don't have it in TINA but here is a schematic of the whole circuit.  The buffers in the bottom right hand corner are the issue.  One out of two boards has the 50-0Hz output clipped and the other board has the 300-0Hz output clipped.  If I bypass the buffer and the output is fine.

  • 0 in reply to Robert Schulte
    Prodigy 30 points

    I just want to make sure you know that I checked all the obvious things one would suspect... the OPA1602 was replaced and power was checked at the pins of the IC.  A 0.1uF ceramic cap is placed right by each power pin to the ground plane... there are 10uF caps a few inches away on each power source.  In the case of the 50-0Hz output U1k and U1l are in the same package and the output at pin 7 is 1V P-P just as expected.  Has anybody experienced a similar issue with these devices?