Earlier this week a group of DigiKey Application Engineers had an informal conversation about Operational Amplifier (op amp) selection. We reviewed the 22 parameters described in DigiKey’s system as we contemplated the fundamental question:
How do I select the best op amp?
DigiKey offers over 30,000 op amps plus a wide range of evaluation boards. Given the variety, we define the best op amp as the one that best suits your project’s needs. This definition is supported by the very existence of so many unique products. Some devices such as the venerable 741 are over 60 years old while others were released this year. Each fills a niche application.
Figure 1: DigiKey’s parametric search for amps.
Tech Tip: The op amp is worthy of additional study. Recommend you refer to these classic resources for additional information. Some of the author’s examples as shown in Figure 2.
Figure 2: Classic books from the author’s library.
Which op amp parameters should I focus on?
As a rule of thumb, there are 3 to 4 parameters that are critical for any given project. Your critical parameters will change depending on the nature of the project. We can illustrate this using a few case studies. The subjectively critical parameters for each case are included in Figure 3.
Example 1: Low-cost battery powered consumer product
With cost as a driving factor, our first instinct is to power the op amp directly from the battery. Consequently, we should prioritize low voltage with allowances for battery charge and discharged voltages.
Rail-to-rail operation is also important as low-voltage operation does not provide the overhead associated with the traditional op amp. For example, the classic 741 is an excellent part for education but will not operate in a 1.5 VDC system.
To further refine the search, we consider the project’s specific signal to select an appropriate Gain Bandwidth Product (GBW). We would also consider cost as well as general availability.
Tech Tip: Common op amps and transistors are informally classified as Jellybean components. These are devices that have been around for many decades and are manufactured by many different OEMs. They are generally low cost and widely available.
Figure 3: Table summary of critical parameters for each example including consumer low power battery, automotive, RF, and education applications.
Example 2: Harsh environment automotive sensor
Automotive parts are subject to temperature extremes. As an example, consider the dashboard of a vehicle operating in Northern Minnesota (home of DigiKey). On an extreme day, the component can go from –30°F (–34°C) to 180°F (82°C) as the vehicle goes from the frigid ambient to full heat with the cabin heater running. In this case, one of the most important parameters is “automotive grade” and compliance with ACE-Q100 environmental stress testing.
Once these critical parameters have been selected, the designer can switch to other considerations such as amplifier type and GBW
Example 3: Radio Frequency
Op amps may be used for high frequency Radio Frequency (RF) applications. The primary consideration is to ensure usable gain into the GHz region by selecting for GBW or the -3 dB point. There may also be consideration for packaging to provide low-impedance PCB layout. Like the other cases, the designer can then select for desirable secondary characteristics.
Example 4: Education
Education is a broad topic with many different needs depending on the student’s knowledge. For first experiments, the ability to breadboard is a critical factor. Advanced students will shift to their requirements such as when they conduct analog experiments with microcontrollers high-speed Analog to Digital Converters (ADC).
Let’s take a moment to mention op amp evaluation boards such as the Texas Instruments LM5401 as shown in Figure 4. This is ideal from an education perspective as the student may explore the amplifier performance without the time-consuming effort of designing a dedicated PCB.
Figure 4: Image of the Texas Instruments LMH5401EVM evaluation board.
Parting thoughts
There are thousands of op amps to meet your circuit needs. Selecting the best op amp demands a project-based approach. We see that each application has a handful of must meet criteria. We use this as our first pass when using the DigiKey parametric search engine. We then refine the search to locate the best op amp for the project.
We would love to hear your thoughts on this topic.
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Do you agree with the tech tip list of resources?
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Can you identify cases where this “critical parameter” worked for you or where it fell short?
Give DigiKey’s op amp selector tool a try and let us know what you think.
Best wishes,
APDahlen
Related information
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About this author
Aaron Dahlen, LCDR USCG (Ret.), serves as an application engineer at DigiKey. He has a unique electronics and automation foundation built over a 27-year military career as a technician and engineer which was further enhanced by 12 years of teaching (interwoven). With an MSEE degree from Minnesota State University, Mankato, Dahlen has taught in an ABET-accredited EE program, served as the program coordinator for an EET program, and taught component-level repair to military electronics technicians. Dahlen has returned to his Northern Minnesota home and thoroughly enjoys researching and writing articles such as this.
Battery powered 1.5–3.5 VDC →
Texas Instruments TLV9062
dirt cheap (pennies in volume)
