Texas Instruments ULN2004AIDR

Overview

ULN2004AIDR from Texas Instruments is a 7-channel high-voltage, high-current Darlington transistor array designed for driving inductive loads such as relays, solenoids, and lamps. Each channel delivers 500 mA collector current, supports 50 V output voltage, integrates input series resistors (10.5 kΩ), and features built-in common-cathode clamp diodes. It operates across −40°C to 105°C and interfaces directly with TTL/5-V CMOS logic.

For engineers reviewing the ULN2004AIDR datasheet, ULN2004AIDR pinout, ULN2004AIDR application, or ULN2004AIDR equivalent, this device serves as a robust, integrated relay-driver solution requiring no external base resistors or flyback protection components - critical for industrial control, automotive body electronics, and programmable logic output stages.

Technical Context

The ULN2004AIDR implements seven independent NPN Darlington pairs, each with a monolithic 10.5-kΩ input resistor enabling direct TTL/CMOS compatibility. Its internal clamp diodes are connected to a shared COM terminal, allowing simultaneous suppression of back-EMF from multiple inductive loads.

Each Darlington stage exhibits low saturation voltage (≤1.6 V at 350 mA input drive), fast switching (tPLH/tPHL ≤10 µs over full temperature range), and high off-state input impedance (II(off) ≤65 µA). The device's thermal design supports continuous operation at up to 105°C ambient when mounted on standard PCBs with adequate copper area.

Key Specifications

Pinout & Package

ULN2004AIDR is housed in a 16-pin SOIC (D) package (7.4 mm × 10.3 mm, 2.00 mm max height), RoHS-compliant, with moisture sensitivity level (MSL) 1 and lead finish NiPdAu.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ULN2003AIDR, ULN2004AIDR offers guaranteed 5 V logic compatibility and reduced external component count; versus STPIC6C595MTR, it provides simpler parallel control and integrated flyback protection - making ULN2004AIDR the preferred choice for deterministic, low-latency relay and lamp switching.

Availability

ULN2004AIDR is available at Aetrix Electronics and suitable for industrial automation, automotive body electronics, and commercial lighting applications requiring stable component supply, long-term lifecycle support, and RoHS-compliant sourcing.

Supply support for ULN2004AIDR 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 specializing in analog, embedded processing, and connectivity technologies, with decades of experience in industrial and automotive-grade power interface solutions.

The ULN2004AIDR belongs to TI's ULN family of Darlington arrays, engineered specifically for robust, low-cost switching of inductive and resistive loads in harsh electrical environments - emphasizing reliability, integration, and ease of use.

FAQ

What is the maximum continuous current per channel for ULN2004AIDR?

The ULN2004AIDR supports a maximum continuous collector current of 500 mA per Darlington channel under specified thermal conditions (T_A ≤ 105°C, adequate PCB copper). This rating assumes proper heat dissipation - exceeding 500 mA risks thermal shutdown or permanent damage. Derating is required above 25°C ambient; consult the datasheet's thermal curves for precise limits at elevated temperatures. ULN2004AIDR maintains this rating across its full operating temperature range.

Does ULN2004AIDR require external flyback diodes when driving relays?

No, ULN2004AIDR does not require external flyback diodes. It integrates seven common-cathode clamp diodes connected to Pin 16 (COM), which safely dissipate inductive kickback energy when switching relays or solenoids. To use this feature, connect Pin 16 to the positive supply rail of the inductive load. Omitting this connection disables clamp protection and may damage the ULN2004AIDR or other system components.

Can ULN2004AIDR be used with 3.3 V microcontrollers?

Yes, ULN2004AIDR accepts 3.3 V logic inputs reliably. Its input threshold (V_I(on)) is specified down to 2 V, and the 10.5-kΩ internal base resistor ensures sufficient drive current even at 3.3 V. However, for marginal noise immunity or worst-case low-V_CC scenarios, verify that the MCU's high-level output voltage exceeds 2.0 V under load. ULN2004AIDR has been validated for interoperability with both 3.3 V and 5 V logic families.

What is the purpose of the COM pin (Pin 16) on ULN2004AIDR?

Pin 16 (COM) is the common cathode connection for all seven internal clamp diodes. It must be connected to the positive supply rail of the inductive load (e.g., +12 V or +24 V) to provide a return path for flyback current. Leaving COM unconnected disables clamp protection and exposes the ULN2004AIDR to destructive voltage transients. ULN2004AIDR relies on this single-pin configuration to simplify PCB routing while maintaining full protection across all channels.

How does ULN2004AIDR differ from ULN2003AIDR in practical design?

ULN2004AIDR includes 10.5-kΩ internal input resistors optimized for 5 V TTL/CMOS logic, whereas ULN2003AIDR lacks these resistors and requires external pull-ups for reliable 5 V operation. ULN2004AIDR also specifies tighter V_CE(sat) and higher input current tolerance across temperature. In practice, ULN2004AIDR reduces bill-of-materials cost and layout complexity - especially in new designs targeting 5 V microcontrollers - while ULN2003AIDR suits legacy 3.3 V or open-collector systems.