Texas Instruments ULN2003AID

Overview

ULN2003AID from Texas Instruments is a 7-channel high-voltage, high-current NPN Darlington transistor array designed for logic-level interfacing to inductive and resistive loads. It delivers 500mA per channel, supports up to 50V collector-emitter voltage, integrates common-cathode clamp diodes, features 2.7kΩ input base resistors for direct TTL/5V CMOS compatibility, and operates across –40°C to 70°C ambient temperature - widely deployed in relay and stepper motor control circuits.

For engineers reviewing the ULN2003AID datasheet, ULN2003AID pinout, ULN2003AID application, or ULN2003AID equivalent, key selection criteria include per-channel sink current capability, integrated flyback diode configuration, thermal derating at elevated duty cycles, input logic compatibility (3.3V/5V), and package-specific R_θJA (88.6°C/W for SOIC-16).

Technical Context

The ULN2003AID implements seven independent Darlington pairs with monolithic integration of input series resistors (2.7kΩ), internal base-emitter pull-downs (7.2kΩ and 3kΩ), and common-cathode clamp diodes tied to the COM pin. Each channel functions as a grounded-emitter, open-collector switch capable of sinking load current while suppressing inductive kickback via the integrated diode path.

It operates in two primary functional modes: inductive load drive (COM connected to coil supply) and resistive load drive (COM floating, external pull-up required). Input logic thresholds are defined by VI(on) ≤ 3V at IC = 300mA, and switching is characterized by tPLH/tPHL ≤ 1μs at 25°C with 50% duty cycle.

Key Specifications

Pinout & Package

ULN2003AID is housed in a 16-pin SOIC (Small Outline Integrated Circuit) package measuring 9.90mm × 3.91mm, with standard JEDEC MS-012AC footprint and gull-wing leads. Thermal performance is characterized by R_θJA = 88.6°C/W and R_θJC(top) = 50.1°C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ULN2003ADR and ULN2003AN, the ULN2003AID offers the best balance of surface-mount compatibility, thermal performance (88.6°C/W), and industry-standard SOIC footprint - making it optimal for volume-manufactured industrial control boards where reflow yield and thermal margin are critical.

Availability

ULN2003AID is available at Aetrix Electronics and suitable for relay control, stepper motor driving, lamp/LED switching, and industrial display interfacing requiring stable component supply and long-term industrial lifecycle support.

Supply support for ULN2003AID 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

Texas Instruments is a global semiconductor leader delivering analog, embedded processing, and connectivity solutions for industrial, automotive, and personal electronics markets.

The ULN200x family was engineered specifically to simplify high-current, high-voltage logic interfacing - targeting cost-sensitive, reliability-critical applications like factory automation, building controls, and appliance motor drives.

FAQ

What is the maximum continuous current per channel for ULN2003AID?

The ULN2003AID supports 500mA continuous collector current per Darlington channel under recommended operating conditions (T_A ≤ 70°C, duty cycle ≤ 100%). Derating is required above 70°C ambient or at elevated duty cycles - Figure 5-4 in the TI datasheet shows maximum current vs. duty cycle for the SOIC package. Exceeding 500mA risks thermal overload and permanent damage.

Does ULN2003AID require external flyback diodes when driving relays?

No, ULN2003AID does not require external flyback diodes when driving relays. It integrates seven common-cathode clamp diodes connected between each collector output (Pins 10–16) and the COM pin (Pin 9). To activate this protection, the COM pin must be connected to the positive side of the relay coil supply - enabling safe recirculation of inductive kickback current.

Can ULN2003AID be used with 3.3V microcontrollers?

Yes, ULN2003AID is fully compatible with 3.3V microcontrollers. Its 2.7kΩ internal input resistors allow direct connection to 3.3V GPIO pins - delivering sufficient base drive (≥1.2mA at 3.3V) to saturate the Darlington pair at up to 300mA output. VI(on) is specified ≤3V at IC = 300mA, confirming reliable turn-on with standard 3.3V logic levels.

What is the purpose of the E pin (Pin 8) on ULN2003AID?

The E pin (Pin 8) is the common emitter terminal shared by all seven Darlington pairs. It must be connected to system ground to complete the current path for all sink outputs. Unlike the COM pin (which serves the clamp diodes), E provides the return path for collector current - grounding E is mandatory for proper operation; leaving it floating disables all channels.

How does thermal performance differ between ULN2003AID and ULN2003AN?

ULN2003AID (SOIC-16) has R_θJA = 88.6°C/W, while ULN2003AN (PDIP-16) has R_θJA = 66.7°C/W - meaning the PDIP version dissipates heat more effectively in still air. For identical power dissipation (e.g., 0.5W), ULN2003AN runs ~15°C cooler. This makes ULN2003AN preferable in thermally constrained through-hole designs, whereas ULN2003AID suits compact SMT layouts where board area is prioritized over thermal margin.