ADA4522 voltage follower config with dual supplies

jwyoungster on Jun 27, 2020

using an ADA4522 (dual pack) for a buffer/inverter setup. so, one of theamps setup as typical volt follower, the other a inverting amp. BOth are driven from an AD8221.

The AD8221 is outputting a 20KHz sine biased at 2V. Vpp on sine = 2V...

When I sweep the freq up to about >190KHz...somehwere in there, the volt follower section appears to slew/clamp, oscillate...while the inverting side looks fine.

+-12V dual supplies on chip. Tried inserting a 332ohm in series with the volt follower input..didnt do anything...tried removing DC bias...did nothing....not driving capacitive load.

just looking for the reason this might be happening....???

jwyounghster@verizon.net

0 harrynsc on Jun 27, 2020 6:34 PM

You didn't say which 4522 is oscillating. Usually, it is too much capacitance on the output pin.

You show an off page reference. What is connected to the output of the op amp? A six foot cable?

Harry
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0 jwyoungster on Jun 28, 2020 12:28 AM in reply to harrynsc

a 1megohm scope probe...with super tight gnd.

no cable..measured right at output of device...no 6ft cable you suggest old boy...

its not oscillating...it appears to slew/osc...up in that freq range......i can post pics if you'd like harry old boy...

just seems very strange guvnr...

figured there might be some errata or such...tip top, righto, let me know if anyone has a clue suggestion...righto.

cheers
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0 harrynsc on Jun 28, 2020 2:12 PM in reply to jwyoungster

jw,

Sorry, I didn't read carefully and thought it was oscillating as you went higher in frequency.

I think it is probably just slew rate limiting. I calculate you should see it above 110 kHz.

See:

https://www.ti.com/lit/an/snoa726/snoa726.pdf

Reduce the amplitude from 2V to 1V and see if that makes a difference.

Harry
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