OPA4192: Question about using OPA 4192 as voltage follower (Buffer Circuit)

Shen Zed

Prodigy 225 points

Part Number: OPA4192
Other Parts Discussed in Thread: TLC2274, , OPA2192, OPA192

HI, I am going to use OPA4192 as voltage follower, buffer circuit. I used TLC2274 before.

I will connect

IN + : ADC Input

IN- : Connect to OUTPUT.

And here is my question.

When I used TLC2274, I didn't put any isolation resistor in the output.

TLC2274 has High cload drive feature but OPA4192 doesn't have. I found High cload feature doesn't need any isolation resistor.

Then, If I use OPA4192 as buffer, then do I need isolation resistor and any capacitor?
If I need, then how can I calculate value?

And If priced doesn't matter then, can OPA4192 replace TLC2274 without any disadavtages as using voltage follower circuit? High Cload? (Unity gain, buffer)

( From the datasheet OPA4192 is much better then TLC2274 in all specs. (BW, Slew rate, low offset voltage), and I think there is no reason to use TLC4192, because OPA4192 is much better. )

And OPA4192 is CMOS OP AMP?

Thanks.

over 3 years ago

0 Raymond Zhang1 over 3 years ago

TI__Mastermind 47966 points

Hi Zed,

When I used TLC2274, I didn't put any isolation resistor in the output. If I use OPA4192 as buffer, then do I need isolation resistor and any capacitor?

It depends. How much Cload capacitive load you are driving? if it is small capacitive load, then you probably do not need Riso. Please provide me a scenario of Cload value in a buffer configuration, I will demonstrate it tomorrow.

Meanwhile, please watch the following video series , and it is fairly well explained.

https://training.ti.com/ti-precision-labs-op-amps-stability-introduction?context=1139747-1139745-14685-1138805-13848

Best,

Raymond

0 Shen Zed over 3 years ago in reply to Raymond Zhang1

Prodigy 225 points

Hi, Raymond.

I just want to use ADC or PWM signal as buffer through OP-AMP.

ADC, PWM signal -> OP AMP -> MCU.

Schematic is very simple. How can I calculate cload capacitve load?

I am still student in EE. Novice. Sorry for not understanding well.

Thanks for your kindness.

0 Raymond Zhang1 over 3 years ago in reply to Shen Zed

TI__Mastermind 47966 points

Hi Zed,

TLC2274 has High cload drive feature but OPA4192 doesn't have. I found High cload feature doesn't need any isolation resistor.

Then, If I use OPA4192 as buffer, then do I need isolation resistor and any capacitor? If I need, then how can I calculate value?

Almost all op amp can be used as for buffer, as long as it meets your BW, Vos. output current sourcing and stability requirements etc. Many op amps are designed as buffer. High performance op amp likes OPA192 (OPA4192 means quad package, OPA2192 =dual, OPA192=single) can certainly use it as buffer, but it may be an overkill, unless the application is very specific for certain performance criteria. In addition, many op amp's datasheets sometimes specify if a part is unity gain stable --> meaning it is good or less problematic to use it as buffer (without further stability compensation).

Enclosed is a thread that may help you to select various op amps for different application.

https://e2e.ti.com/support/amplifiers/f/14/t/891120

Schematic is very simple. How can I calculate cload capacitve load?

The quickest way to find out if an Op Amp has possible stability issues is to read the datasheet first. For instance in OPA192, the open loop bode plot is showing you that the op amp rolls off at -20dB/decade with good phase margin(67.5 degree) up to 10MHz. This indicates that you may use it as buffer.

Next, you will do a pspice simulation to verify if an Op Amp is stable with a given load condition. Large capacitive load will always affect the stability of the op amp. Therefore, you have to simulate and pay attention to closed loop stability.

From the simulation, you check for the phase margin at the unity gain bandwidth for loop stability. The following videos explain Riso compensation method, if you have stability issues when dealing with large capacitive load. There are other op amp compensation methods, but Riso compensation methods work well for large capacitive load.

Enclosed is an article about how to perform small signal injection in Op Amp circuit. The loop stability method in the video training is done differently, but the principle is the same.

/cfs-file/__key/communityserver-discussions-components-files/14/OPA192-buffer-07312020.TSC

/cfs-file/__key/communityserver-discussions-components-files/14/7827.Small-Signal-Injection-Loop-Gain-in-Japanese.pdf

https://training.ti.com/ti-precision-labs-op-amps-stability-measuring-system-stability?context=1139747-1139745-14685-1138805-13851

https://training.ti.com/ti-precision-labs-op-amps-stability-capacitive-loads?context=1139747-1139745-14685-1138805-13952

The best way to learn in how to perform the op amp loop compensation is practicing on your own or follow a particular example. Hope the note and video training series will help you better understanding in op amp compensation techniques.

If you have any questions, please let us know.

Best,

Raymond

0 kai klaas69 over 3 years ago in reply to Shen Zed

Guru 140200 points

Hi Shen,

why do you want to connect a load capacitor to the output of OPAmp at all? Do you want to provide some low pass filtering?

Kai

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OPA4192: Question about using OPA 4192 as voltage follower (Buffer Circuit)