Q: Using the DK parametric search function to select an op amp

This article will discuss how to use Digi-Key's parametric search function to select an op amp. We assume that you already have a theoretical knowledge of op amps and understand what you are searching for, and based on that, we will guide you on how to effectively use the parameter filtering function to obtain a condensed list of candidate materials. If you need to understand the theoretical and application aspects of op amps, it is recommended to move to this post.

When shopping for an op amp, the first thing you need to do is find this type of product. One way is to simply search for "op amp" and click on the desired main product family near the top of the results page, where you can easily click through to see the relevant results.

The vast majority of op amp materials that engineers typically require are included here, but there are a small number of other product families that may contain related products with more specialized use cases.

If you are looking at the "Linear – Amplifier – Instrumentation, Op Amp, Buffer Amplifier" product family, click the "Integrated Circuits" link in the breadcrumbs at the top of the results page to see a list of all product families in that product category. Other product families that contain op amp products are listed next to each other, and the product family names are all prefixed with "Linear-Amplifier-____".

After finding the main op amp product family, you need to choose from a large number of parametric filters.

People often ask "Which one should I choose first"? So the following will briefly describe the usage of each filter condition in order from left to right. The generic answer in engineering ("depending on…") applies here as well. Most applications have some basic non-negotiable requirements, such as supply voltage and package type (surface mount vs. through-hole). Therefore, it is necessary to start screening from the daily necessary conditions. Beyond that, there are usually only one or two performance parameters that are particularly important, so it needs to be confirmed which parameter is critical for a given application. This is a matter of theory and application, and will not be repeated in this article.

manufacturer

If you're a big fan of a brand or have sworn off a brand, you can choose from this column to match those preferences. This simple filter avoids confusion due to the product confusion caused by the recent mergers and acquisitions of electronics companies.

Package

Packaging refers to how the product is packaged and includes some purchasing implications – say, you want to buy 3 op amps in total, you don't need to look at the results for the package style with a minimum order of 5,000, and you may not be happy to buy 3 op amps in total. Items are purchased in neatly packaged Digi-Reel packages. In this case, you can choose all options except "Digi-Reel" and "Tape and Reel". For op amps, however, the "cut-to-reel" and "tube" lists already cover a large number of available manufacturer part numbers.

series

The manufacturer's brand or product line name is listed in this condition for you to choose from. While this filter is not as practical for op amps as some other product families, it is listed for specification and DK business practice.

Part status

Here you can filter the list of products based on their lifecycle stage. There is no doubt that "active" (in current production, with no announced imminent end of production) materials are preferred for new design activities. And the combination of "in stock" and "discontinued" is probably just for pranks. Until now, parameter columns have been almost boilerplate content, and these concepts can be translated and applied to most Digi-Key product portfolios. Now, let's move on to the actual op amp-related filters…

Amplifier type

This parameter reflects the primary adjective used by the supplier's marketing team to describe the material. Many of the values ​​listed here represent significant differences in general-purpose op amp architectures (eg, meter, isolation, and logarithm), and are therefore significant and significant enough to be justified as primary adjectives for materials. There are other values ​​in this column that describe relatively small implementation differences of the underlying op amp (JFET, CMOS), reflect undefined marketing terms (audio), reflect common architectural classes that are not mutually exclusive with other terms (voltage Feedback, Current Feedback), and the blunt but not particularly helpful term (generic).

Use this parameter with care and caution due to the mixed environment involved and the non-orthogonal nature of the optional values. While in most cases it's safe to choose the distinguishing differences of the basic op amps (instrument amps, isolation amps, etc.), if the product you're looking for is represented by the standard op amp notation, it may lead to more unnecessary trouble.

Number of circuits

If you have a requirement for the number of different amplifier circuits in a package, you can choose here. For this amplifier feature, one- and two-way products are the most selected, and three-way products are often developed for video applications.

output type

This condition reflects the output structural characteristics of the product. This parameter is still a work in progress, and while the data set from which it is derived is fairly accurate, it is far from complete—about half of the materials in this product family have yet to be assigned a value. Therefore, if you have selected parameters in this column and wish to obtain comprehensive screening results, select the dashed (null) value to avoid missing viable candidates. Although you will need to filter out a lot of false positives, it avoids hastily removing half of your product mix.

Slew rate

The slew rate characteristics of an amplifier are affected by a variety of factors, and each manufacturer does not manufacture op amps to a single standard. Therefore, you should treat the data shown here as approximations with many qualifications not shown in parametric searches. When filtering with this parameter, it is recommended to include values ​​that deviate slightly from the target value, values ​​that are significantly outside the target value range, and dashed values. This minimizes the risk of removing valid product candidates.

Gain Bandwidth Product (GBP) and -3dB Bandwidth (BW)

GBP and -3dB BW are common metrics for measuring the overall "speed" of an amplifier and are directly related to the slew rate. It is also recommended that you broaden the selection of parameters – you only need to "choose the continent where you live, not the street address" for the amplifier.

DO NOT SELECT BOTH Columns!!! CHOOSE ONE OF THEM!!! It is rare (less than 10% of the current list) to use both parameters to characterize an amplifier. Voltage-feedback products tend to use GBP, while current-feedback products are typically characterized by -3dB BW; the more application-independent sensitivity values ​​in both architectures are also different. At the time of writing this post, the DK website is under recent development, so it is not possible to include products with dashed (unspecified/waiting to be populated/not applicable) values ​​in the search results for parameters with scoped search enabled. Because both parameters are defined for the same material, which is a rare case, if selected in both parameter columns (even if all available values ​​in both columns are selected), it will filter out More than 90% of the materials in the product family.

Current Input Bias

Entries in this column usually represent "typical" characterization values ​​provided by the manufacturer, which may be an order of magnitude less than the guaranteed maximum value (if provided by the manufacturer). When bias current is the driving factor, the values ​​should be chosen according to stricter requirements than the error tolerance, which can reduce the difference between the "typical" and "maximum" values ​​and help to condense the list of results faster , to select the most qualified candidates.

Voltage input offset

The values ​​in this parameter column reflect the "Typical" or "Maximum" values, which can also vary by a factor of ten. Offset voltage appears to be more likely than bias current to reach the specified guaranteed limits, but the test conditions for which quoted values ​​apply can vary widely. For example, some values ​​may only apply to a constant temperature environment of 25°C, while other values ​​may apply to temperatures outside the material's rated temperature range. Considering the variability in the qualifying conditions for the values ​​listed in this parameter column, some strategies need to be taken when an application uses offset voltage as a drive criterion. If the parameter selection criteria are more stringent than the application requires, the number of false positives that must be screened can be reduced, but some viable candidates may also be screened. On the other hand, expanding the selection at the beginning helps to limit the application of other important selection criteria, and after selection, you can go back to the offset voltage column and make the final selection accordingly.

Current – Power

The values ​​in this column reflect the manufacturer's typical or guaranteed maximum specifications, and factors such as the supply voltage used and product temperature can affect the actual observed behavior. While this parameter is useful for narrowing down the initial candidate material in applications where a clear power budget exists, it is often used to make the final decision in selecting candidate materials based on other criteria and is not a primary consideration in material selection.

Current – Output/Channel

The values ​​in this column reflect the maximum value indicated by the manufacturer. If an application requires one product to supply a large output current, it is recommended to select all products with marked values ​​greater than the design requirements. If the huge output current is expected to last for a long time, choose a product with some margin between the application requirements and the stated value; usually the results of selecting a product directly by the limit of this parameter will not be very good .

Voltage – Power, Single/Dual (+/-)

Many applications come pre-set with the available supply voltage, and in this case this may be the first parameter you want to choose. The values ​​shown in this column generally take two forms:

The ±X~Y form represents a "dual supply" product, requiring the signal to be biased near the midpoint between the supplies

The 2U~2W and ±U~W formats indicate that the product supports "single supply" operation, which means that the common-mode input range includes the negative supply rail. For "single supply" products, it is common but not necessary for the output voltage to float near the negative rail; if this is a necessary feature, verify against the datasheet before making a final selection.

When selecting a product based on the available input voltage, the first thing to determine is whether the external circuit requires a "single-supply" amplifier, that is, whether the common-mode input will be very close to the negative rail. If so, you do not need to select any parameter values ​​in the form ±X~Y. If not, it is advisable to consider the total span between the power supply rails, as this allows you to look at the options to the left of this column when choosing a product that supports a single power supply.

For the first time, all values ​​containing the expected supply voltage can be selected. Better results are usually obtained when the expected power supply is closer to the middle or upper end of the product's allowable range, as the minimum power supply value is usually slightly larger than the sum of the product's headroom requirements. A product may be technically compliant with a working voltage of only 5V, but in that case it's not very useful for many applications if the input and output voltages can only float in the 0.25V range…

Operating temperature

In a way (sorry…), this parameter describes additional information about the material, equivalent to a description of the material itself. When the manufacturer provides guaranteed limits for non-ideal material behavior such as bias current or offset voltage, that limit will be limited by temperature. Usually, it is referred to as the rated operating temperature range of the material. Whenever possible, select materials with a rated temperature range that includes the expected operating conditions. This way, you don't have to choose to run the device outside the limits specified by the material in the event of a problem. While physics does have some margin in terms of temperature ratings, you're on your own if you violate the limits of those ratings…

Mounting Types, Packages/Enclosures, and Vendor Device Packages

The Mounting Type parameter lets you choose from several common physical product package categories, and can be considered a macro filter for other package parameters. The package/enclosure parameter uses a standardized nomenclature to represent the physical product package, while the vendor product package uses a nomenclature arbitrarily chosen by the vendor to reflect this. Select the package you want. As a looser rule of thumb, if you want small materials, look for materials with a lot of letters in the second half of the alphabet in the package number…

Original title: Operational amplifier selection: This nanny-level strategy will make you fast and accurate!

Article source: [WeChat official account: DigiKey] Welcome to add attention! Please indicate the source of the article reprint.

Reviewing Editor: Tang Zihong

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