STMicroelectronics ULQ2803A

Overview

ULQ2803A from STMicroelectronics is an 8-channel Darlington transistor array optimized for 5 V TTL and CMOS logic interfacing, featuring integrated clamp diodes, 500 mA continuous output current per channel, 50 V off-state voltage rating, and DIP-18 package with input-opposite-output pinout. It drives inductive loads such as relays, solenoids, and stepper motor windings in industrial control modules.

For engineers reviewing the ULQ2803A datasheet, ULQ2803A pinout, ULQ2803A application, or ULQ2803A equivalent, key selection criteria include input resistor value (2.7 kΩ), VI(ON) threshold (≤3.0 V at IC = 200 mA), VCE(SAT) (≤1.1 V at IC = 100 mA), thermal resistance (55 °C/W), and parallel-output capability for current scaling.

Technical Context

The ULQ2803A integrates eight independent NPN Darlington pairs with common-emitter outputs and monolithically integrated flyback diodes-each rated for 500 mA continuous and 600 mA peak collector current. Its 2.7 kΩ on-chip input resistor sets VI(ON) compatibility with 5 V TTL/CMOS logic levels while limiting base drive current to ~1.35 mA at 3.85 V input.

Designed for direct logic-to-load interfacing without external biasing, it supports paralleling of outputs to increase current capacity and operates across –40 °C to +105 °C ambient temperature, with thermal derating governed by RthJA = 55 °C/W and total package power dissipation limited to 2.25 W.

Key Specifications

Pinout & Package

ULQ2803A is housed in a standard 18-lead plastic dual in-line package (DIP-18) with copper leads and ECOPACK® environmental compliance. Pin numbering follows top-view orientation with inputs (1–8) on one side and corresponding outputs (11–18) directly opposite - enabling straight-through PCB trace routing and minimizing crosstalk.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ULN2803A, ULQ2803A reduces external component count and improves layout efficiency; compared with TB6570FG, it offers lower system cost and simpler integration for multi-channel 500 mA switching, though with lower efficiency and no PWM-native interface.

Availability

ULQ2803A is available at Aetrix Electronics and suitable for industrial relay control, stepper motor phase driving, solenoid actuation, and LED array switching requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for ULQ2803A 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 ULQ2803A belongs to ST's high-voltage Darlington array product line, engineered specifically for robust logic-to-inductive-load interfacing in harsh industrial environments with minimal external components.

FAQ

What is the maximum safe continuous output current per channel?

The ULQ2803A is rated for 500 mA continuous collector current per Darlington channel at TA ≤ 70 °C with adequate PCB copper area. At 105 °C ambient, derating applies per Figure 13 in the datasheet: maximum continuous current drops to approximately 350 mA to maintain junction temperature below 150 °C, assuming RthJA = 55 °C/W and no forced airflow.

Can outputs be paralleled, and what is the resulting current capability?

Yes - outputs may be paralleled to increase current capacity. Two channels yield ~900 mA continuous (accounting for mismatch and thermal coupling), and three channels support ~1.3 A. Derating is required: total package power must remain ≤2.25 W, and shared emitter (Pin 9) and clamp cathode (Pin 10) connections must handle summed current with appropriate trace width and thermal relief.

Does ULQ2803A require external flyback diodes when driving relays?

No - each channel includes a monolithic clamp diode with cathode connected to Pin 10. When driving a relay coil between VCC and an output (e.g., Pin 11), Pin 10 must be connected to the same VCC rail. This configuration safely recirculates inductive energy without external components, verified per Figure 9 test circuit and IR ≤100 µA at 105 °C.

How does ULQ2803A differ from ULN2803A in practical circuit design?

ULQ2803A integrates 2.7 kΩ input resistors, enabling direct connection to 5 V TTL/CMOS outputs without external biasing. ULN2803A lacks these resistors and requires eight discrete 2.7 kΩ pull-ups. This makes ULQ2803A preferable for space-constrained layouts and automated assembly, while ULN2803A offers flexibility for non-standard logic voltages or adjustable input thresholds.