STMicroelectronics ULN2805A

Overview

ULN2805A from STMicroelectronics is an 8-channel Darlington array IC designed to sink high-current TTL/Schottky TTL logic outputs, with each channel rated for 350 mA continuous output current, 50 V off-state voltage, and integrated clamp diodes for inductive load protection. It is used in industrial relay drivers, stepper motor controllers, and LED matrix displays where high-current sinking capability and logic-level compatibility are required.

For engineers reviewing the ULN2805A datasheet, ULN2805A pinout, ULN2805A application, or ULN2805A equivalent, key selection criteria include guaranteed 350 mA per channel sink current at TTL-compatible input thresholds (Vi(on) ≤ 2.4 V), common-emitter Darlington architecture with integral suppression diodes, and DIP-18 input-opposite-output layout for simplified PCB routing.

Technical Context

The ULN2805A implements eight independent NPN Darlington pairs with shared emitter terminals and built-in flyback diodes connected anode-to-emitter, enabling direct drive of inductive loads without external protection components. Each channel features a minimum DC current gain (hFE) of 1000 at IC = 350 mA and VCE = 2 V.

It is optimized for standard and Schottky TTL interfacing: input threshold (Vi(on)) is specified at 2.4 V with IC = 350 mA, and input current (Ii(on)) is 1.25 mA at Vi = 3 V - confirming robust low-voltage TTL compatibility without external pull-up or level-shifting circuitry.

Key Specifications

Pinout & Package

ULN2805A is housed in an 18-lead plastic DIP (dual in-line package) with copper leadframe, measuring 23.24 mm × 8.5 mm × 3.3 mm (0.915″ × 0.335″ × 0.130″), featuring input pins on one side (1–8) and corresponding output pins on the opposite side (10–17), with pin 9 as common emitter and pin 18 as ground.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ULN2803A and TD62003APG, ULN2805A uniquely guarantees 350 mA continuous sink current specifically for Schottky TTL interfaces, with tighter V_i(on) (≤2.4 V) and validated performance at Vi = 3 V - making it optimal for legacy TTL systems requiring margin against voltage droop and temperature drift.

Availability

ULN2805A is available at Aetrix Electronics and suitable for industrial relay control, stepper motor phase driving, LED matrix displays, and printer head actuation requiring stable component supply across long-lifecycle embedded programs.

Supply support for ULN2805A 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 ULN280x series belongs to ST's high-voltage, high-current driver product line, engineered specifically for logic-to-power interfacing in industrial automation, factory control, and electromechanical actuation systems.

FAQ

Can ULN2805A drive 48 V solenoids?

No. ULN2805A has a maximum output voltage rating of 50 V, but its absolute maximum continuous collector-emitter voltage is specified at 50 V with strict derating above 25 °C ambient. For 48 V solenoids, transient voltage spikes during turn-off may exceed this limit even with internal clamp diodes. Use only with 24 V or lower inductive loads unless external TVS clamping is added.

Is ULN2805A pin-compatible with ULN2803A?

Yes - ULN2805A shares identical DIP-18 pinout, input-opposite-output layout, and common-emitter configuration with ULN2803A. However, ULN2805A omits the internal 2.7 kΩ input resistors present in ULN2803A, requiring external current-limiting resistors if driving from CMOS sources with high output voltage.

What is the maximum allowable duty cycle at 350 mA per channel?

At 350 mA continuous per channel and Tamb = 25 °C, ULN2805A dissipates ~0.46 W per channel (350 mA × 1.3 V). With total package P_tot = 2.25 W and R_{th j–amb} = 55 °C/W, sustained 350 mA across all 8 channels exceeds thermal limits. For full-load operation, duty cycle must be limited to ≤35% to maintain T_j < 125 °C.

Does ULN2805A require external flyback diodes when driving relays?

No. ULN2805A integrates clamp diodes with cathodes tied to pin 18 (V_CC) and anodes connected internally to each emitter. When the common emitter (pin 9) is grounded and V_CC is connected to the relay coil's positive rail, these diodes provide complete flyback protection without external components.