STMicroelectronics ULN2002A

Overview

ULN2002A from STMicroelectronics is a high-voltage, high-current seven-channel Darlington array with integrated clamp diodes, rated for 500 mA continuous output current per channel (600 mA peak), 50 V output voltage, and TTL/CMOS/PMOS-compatible inputs optimized for 14–25 V logic systems. It serves as a robust interface between low-power control logic and inductive loads such as relays, solenoids, and DC motors in industrial automation and appliance control.

For engineers reviewing the ULN2002A datasheet, ULN2002A pinout, ULN2002A application, or ULN2002A equivalent, key selection criteria include its 50 V open-collector output rating, 1.1 V typical V_CE(SAT) at 200 mA, input compatibility with 14–25 V PMOS logic, thermal resistance of 70 °C/W (DIP-16), and built-in flyback diode protection - all critical for reliable relay-driving designs.

Technical Context

The ULN2002A integrates seven independent NPN Darlington pairs with common-emitter outputs and on-chip suppression diodes connected from each collector to the common cathode pin (pin 9). Each channel operates as an open-collector switch, requiring external pull-up to load supply, and accepts direct drive from 14–25 V PMOS logic without level-shifting.

Its input stage is designed for high-impedance, low-leakage operation (≤65 µA at 85 °C), while the Darlington configuration delivers high DC current gain (h_FE ≥1000 at I_C = 350 mA) and fast switching (t_PLH/t_PHL ≤1 µs), enabling efficient control of moderate-power inductive loads in space-constrained PCB layouts.

Key Specifications

Pinout & Package

ULN2002A is supplied in a 16-pin plastic dual in-line package (DIP-16L) with copper leadframe for enhanced thermal performance. Pin numbering follows standard DIP convention (pin 1 at top-left corner, notch or dot marking orientation).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar Darlington array applications.

Compared with ULN2003A and TD62003APG, ULN2002A uniquely balances 14–25 V PMOS input compatibility, integrated protection, and industry-standard DIP-16 pinout - making it the optimal choice for retrofitting legacy industrial controls without redesign.

Availability

ULN2002A is available at Aetrix Electronics and suitable for industrial relay control, appliance motor interface, automated test equipment, and thermal print head driver applications requiring stable component supply and long-term obsolescence management.

Supply support for ULN2002A includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing analog, digital, and mixed-signal ICs for automotive, industrial, and consumer markets.

The ULN2002A belongs to ST's high-voltage interface product line, engineered specifically for robust, low-cost driving of inductive loads in harsh industrial environments where reliability and ease of integration are critical.

FAQ

Can ULN2002A drive a 24 V relay coil drawing 40 mA?

Yes. With a 24 V supply and 40 mA coil current, ULN2002A operates well within its 500 mA continuous rating and 50 V output voltage limit. Its typical V_CE(SAT) of 1.1 V at 200 mA ensures only 44 mW power dissipation in this case, resulting in negligible self-heating and high reliability over extended duty cycles.

Is a pull-up resistor required on the output pins?

Yes. ULN2002A outputs are open-collector Darlington sinks, so each output requires an external pull-up resistor connected to the load's positive supply rail. For a 24 V relay with 40 mA coil current, a 620 Ω resistor provides proper bias while limiting power loss to <1 W at full on-time.

What is the purpose of pin 9 (COM)?

Pin 9 is the common cathode connection for all seven internal clamp diodes. It must be tied to the positive terminal of the inductive load supply (e.g., +24 V) to provide a low-impedance path for flyback current when the Darlington turns off - preventing voltage spikes that could damage the IC or adjacent circuitry.

How does ULN2002A differ from ULN2003A in practical use?

ULN2002A accepts 14–25 V PMOS logic inputs directly, while ULN2003A is specified for 5 V TTL/CMOS. Using ULN2003A with 18 V PMOS signals risks excessive input current and potential latch-up. ULN2002A's input structure is hardened for higher voltages, making it the correct choice for legacy PMOS-based control systems.