Op Amp Condition and Parameter Introduction

Problem:
What do the op amp conditions and parameters mean and what impact do they have on circuit design?

Solution:
This page is about op amp data sheet conditions and parameters. When op amps are qualified a sampling of the devices is exposed to certain electrical and thermal conditions. These conditions are listed on the data sheet in a column usually called "TEST CONDITIONS". The test results, or parameters, are usually placed in one or more columns to the right of the conditions. These are the parameters the successful designer must use to select an appropriate device and to then design the application.

Another location where the test conditions and parameters are found is in graphs. The graphs display an array of data to communicate how a parameter changes with changes in test conditions.

It is important to evaluate both the parameter and the test conditions for that parameter. The parameter can be best reproduced in an application when the test conditions are also similar. For example, a device whose input offset voltage, V_IO, is measured at V_IC=V_DD/2 could not be expected to have the same V_IO when V_IC=1V.

Links from this page are arranged to allow the designer to have speedy access to information about op amp conditions and parameters. Their definitions, typical abbreviations, and units appear in Op Amp Condition and Parameter Abbreviations and Op Amp Parameter Information.

While these conditions and parameters are the ones most commonly used at Texas Instruments, the same ones may go by different names and abbreviations at other manufacturers. Not every condition or parameter listed here may appear in the data sheet for a given op amp. A data sheet for an op amp that is intended only for ac applications may omit detailed dc offset information and vice versa (some ac data may be omitted for devices intended for dc applications). Since there is no such thing as an ideal op amp, or one that is universally applicable, the selection of any op amp must be based on an understanding of what particular parameters are most important to the application.

If a particular parameter that is important for an application cannot be found in the data sheet, a review of the application may well be in order and another part might be more suitable. Texas Instruments manufactures a broad line of op amps that can implement almost any application. The inexperienced designer could easily select an op amp that is totally wrong for the application. Trying to use an audio op amp with low total harmonic distortion in a high-speed video circuit, for example, will not work — no matter how superlative the audio performance might be.

Some parameters have a statistically normal distribution. The typical value published in the data sheet is the mean or average value of the distribution, with one exception, offset voltage. The average input offset voltage, V_IO, is normally close to zero but there is always some variation between devices. Therefore, the typical value listed for offset voltage is the mean or average value of the 1 value. This means that in 68% of the devices tested, the parameter is found to be ± the typical value or better. Texas Instruments currently uses 6 to define minimum and maximum values.

Also refer to the following related links:
Op Amp Parameter Information
Op Amp Condition and Parameter Abbreviations

These pages were extracted from Op Amps For Everyone, Chapter 11, by Bruce Carter, Ron Mancini–Editor in Chief.
Copyright © 2000, Texas Instruments Incorporated