Amplifier settling time.

martin b

Other Parts Discussed in Thread: OPA350

Hi.

I have been reading: “TIDU181, 400KSPS, 4-Channel MUX DAQ System For High Voltage Inputs”

and in reference to Figure 14: Back to Back Diode in Traditional Op Amp Introduces Settling Time Delay, page 13 the author comments:

“To achieve the fastest settling performance, it is important to select an amplifier without back to back diodes at its inputs as shown in Figure 15.”

How do I know which op amps have or do not have these back to back diodes at the inputs? and if I use a very fast slew op amp with input protection diodes, are there any issues for or against that I should know about?

Thanks

m.b

over 10 years ago

0 Marek Lis over 10 years ago

TI__Guru 68541 points

Martin,

Without getting into the merits of the statement you quoted about the relationship between the settling time and back-to-back input protection diodes (this usually becomes problem in certain mux’ing configurations), you can find in most of our newer datasheets a simplified diagram showing the diodes – see examples below.

For the older datasheets that may not show them, a rule of thumb is that most of the bipolar input op amps (IB>1nA) as well as high voltage CMOS op amps (Vsupply>+/-5V) require these diodes to prevent EOS damage whereas low supply CMOS (Vsupply<+/-5V) and most JFET input op amps do not need them.

For more info, please read the blog below:

http://e2e.ti.com/blogs_/archives/b/thesignal/archive/2012/03/21/differential-input-clamps-can-they-affect-your-op-amp-circuits.aspx

0 martin b over 10 years ago in reply to Marek Lis

Intellectual 560 points

Thanks for the reply Marek, one last thing does the OPA350 have input protection diodes? I cant seem to make it out from the data sheet for this part, is there another tell tale sign?

cheers

m.b

0 Marek Lis over 10 years ago in reply to martin b

TI__Guru 68541 points

Martin,

I had designed OPAx350 family some fifteen years ago and since it is fabricated on low voltage CMOS process there is no need for back-to-back input protection diodes.

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Amplifier settling time.