Instead of using multiple discrete transistors to build Darlington pairs, you can use a ULN2003 or one of its variants. Here’s where you can find a ULN2003 datasheet.
IoT products, environmental products, and anything else that needs analog sensor fusion will operate at a variety of signal levels. The signal type also varies from sensor to sensor with different frequencies and signal levels. Your signals need to be collected and amplified before you can use the results in a larger digital system. Your typical response might be to use an op-amp array for applications involving multiple signals from sensors, but you have another option to amplify signals and send them to a downstream load with high impedance.
A Darlington pair is one type of circuit that provides very high gain for low-level currents. In essence, these components act like a transimpedance amplifier, which is then used to drive a high impedance load, such as an ADC. Rather than build out a Darlington pair from discrete transistors, you can use a transistor array in a standard surface-mount or through-hole package.
One popular option is the ULN2003, which is designed to interface with TTL and CMOS devices. These components are excellent choices for working with high voltage analog systems and can be brought into complex power regulation circuitry, discrete amplifiers, and other applications where low-level currents need high gain. Here’s where you can find a ULN2003 datasheet, CAD data, and sourcing information to help you create your PCB.
Using the ULN2003 and its Variants
Like most components, the ULN2003 transistor array is part of a family of components produced by a range of manufacturers. The ULN200X family of components comprises transistor arrays for a number of different applications and each of these variants has different features and ratings. The ULN2001 and some ULN2002 variants are currently obsolete, but many ULN2002-ULN2004 components are currently in production by many manufacturers. A ULN2003 datasheet normally shows the Darlington pairs as buffers with a diode on the output. This is shown in the logic diagram below.
Pinout and logic diagram for the ULN2003AD from Texas Instruments datasheet.
As can be seen above, the ULN2003 is a 16-pin IC with seven Darlington pairs; the transistors used in each Darlington pair are NPN BJTs. The ULN2003 is designed to interface with TTL and CMOS devices, and the output can be used to drive loads up to 50 V and 500 mA. The ULN2004A and its ULQ2004A variant allow it to interface directly from CMOS devices. For lower-cost products, the ULN2002 can be used to interface with PMOS devices.
The output characteristics of these components make them a good choice for driving inductive loads as the output diode dissipates voltage spikes on the output. The supporting resistors are diodes for which the input and output are integrated into the package, which reduces the cost for a driver circuit. A typical application is driving a motor, which has inductive input impedance.
While most ULN2003 components are designed to operate up to 50 V, one variant is the ULN2003V12DR, which operates up to 20 V. The input features an RC snubber circuit on the input (gate) of an NFET, where the input damps higher frequency noise to provide stable output to an inductive load. An example application for this variant and other ULN2003 variants would be driving a stepper motor with four of the outputs, which leaves 3 outputs leftover for other functions.
Footprints and Packages
These components are available as surface-mount or through-hole components. Overall, this reduces the footprint of your driver system for a range of applications. Typical packages are 16-pin DIP/PDIP, SOIC, SO, or TSSOP. Because the packages for these components are standardized, a designer could create a footprint for their component from the ULN2003 datasheet, or it could be copied from another component with the same package/pin count.
What’s in a ULN2003 Datasheet
As with most components, the ULN2003 datasheet will show the block diagram, logic diagram, and or circuit diagram for each Darlington pair circuit in the component. One point you’ll notice from a ULN2003 datasheet is the various temperature ratings for different ULN2003 variants. The same points apply to other ULN200X components. Temperature ratings should be checked in the ULN2003 datasheet as this will determine the ideal application for each variant. For systems that need to drive large inductive loads, the environment may be rather harsh and would require the driver IC to withstand high temperatures. Each ULN2003 variant will be called out with a string of letters, which corresponds to different ratings and footprints.
Because the specific ratings and footprints for the ULN2003 may vary for different variants, it helps when you have access to a service that helps aggregate these specifications into a single location. So where can you find all these component details aggregated into a single location? The answer is to use an electronic components search engine. This type of service aids component comparisons and helps you narrow down to the exact variant and package you need for your driver circuitry.
In addition to basic electrical output specifications, temperature ratings, and package size, you’ll find some other important data from the right search engine:
- CAD models. With the right search engine, you won’t need to create 2D or 3D CAD models for your components.
- Sourcing information. When you need to source components at scale, you need to see component stocks, prices, minimum order quantities (MOQs), and lead times.
- Approved vs. unapproved distributor list. To prevent counterfeits, you should only source your components from approved distributors.
- Lead-free and RoHS compliance. Instead of looking through datasheets to ensure compliance, it helps to see RoHS and lead-free compliance directly in your search results.
This helps you compare specifications, CAD model access, and prices for multiple components in a single window. Some example search results are shown below.
ULN2003 search results for in-stock and environmentally compliant components from Ultra Librarian.
When you need to find a ULN2003 datasheet or one of its variants, you can use the electronic parts search features in Ultra Librarian. This convenient tool gives you access to verified CAD models in vendor-specific and vendor-neutral file formats, and you can quickly import these models into popular ECAD applications. You’ll also be able to see updated sourcing information from authorized worldwide distributors. All the component data you’ll find on Ultra Librarian can be accessed at no cost and are verified from component manufacturers.
Ultra Librarian helps you build your component footprint libraries by compiling all your sourcing and component information in one place. Working with Ultra Librarian sets up your team for success to ensure any design is going through production and validation with accurate models and footprints to work from. Register today for free!