ULN2004A Technical Summary

ULN2004A High-Voltage, High-Current Darlington Transistor Array

Overview

The ULN2004A is a high-voltage, high-current Darlington transistor array designed for interfacing between low-level logic circuitry and multiple peripheral power loads. This device is part of the ULN200x series, which includes seven NPN Darlington pairs capable of sinking up to 500 mA per channel. The ULN2004A is particularly suited for driving relays, lamps, LED displays, stepper motors, and other high-current or high-voltage loads.

This component is available in both dual in-line (DIP) and small-outline IC (SOIC) packages, designated as the ULN20xxA and ULN20xxL series respectively. These variants are electrically identical, providing flexibility in board design and space constraints.

Features

Seven Darlington transistor pairs with common emitters
Output current rating of 500 mA per channel (600 mA peak)
Output voltage capability up to 95 V
Integrated suppression diodes for inductive load transient protection
Compatible with TTL, DTL, PMOS, and CMOS logic levels
Inputs pinned opposite outputs to simplify board layout
Available in 16-pin DIP (ULN2004A) and SOIC (ULN2004L) packages
Wide operating temperature range

Applications

The ULN2004A finds use in numerous applications requiring interface between low-power digital circuits and higher power loads:

Relay drivers
Stepper motor controllers
LED display drivers
Incandescent lamp drivers
Logic buffers
Hammer drivers for dot matrix printers
General purpose switching applications

Electrical Characteristics

Absolute Maximum Ratings

Output Voltage (V_CE): 95 V
Output Current (I_C): 500 mA per channel
Peak Output Current (I_C peak): 600 mA per channel
Input Voltage (V_IN): 30 V
Power Dissipation (P_D): 2.25 W (DIP), 1.4 W (SOIC)
Operating Temperature Range: -20°C to +85°C
Storage Temperature Range: -55°C to +150°C

Electrical Specifications (T_A = 25°C unless otherwise noted)

Input Clamp Voltage (I_IN = 3.0 mA): 1.5 V max
Input Current (V_IN = 5 V): 2.5 mA max
Output Saturation Voltage (I_C = 350 mA, I_IN = 0.25 mA): 1.6 V max
Output Leakage Current (V_CE = 50 V, V_IN = 0): 100 μA max
Current Gain (I_C = 350 mA, V_CE = 2 V): 1000 min
Output Clamp Voltage (I_C = 350 mA): 1.6 V max

Package Information

16-Pin Dual In-Line Package (DIP)

Package Designation: ULN2004A
Package Type: PDIP-16
Dimensions: 19.3 mm x 6.35 mm x 4.57 mm
Pin Spacing: 2.54 mm (100 mil)
Row Spacing: 7.62 mm (300 mil)
Lead Material: Copper alloy
Lead Finish: Matte tin

16-Pin Small Outline IC Package (SOIC)

Package Designation: ULN2004L
Package Type: SOIC-16
Dimensions: 9.9 mm x 3.9 mm x 1.75 mm
Pin Spacing: 1.27 mm (50 mil)
Lead Material: Copper alloy
Lead Finish: Matte tin

Functional Description

The ULN2004A contains seven Darlington transistor pairs, each featuring high-voltage outputs with common-cathode clamp diodes for switching inductive loads. Each channel is rated at 500 mA and can withstand peak currents of 600 mA. The Darlington configuration provides high current gain, allowing small input currents to control much larger output currents.

The integrated suppression diodes are connected between each output and the COM pin (pin 9), which must be connected to the positive supply voltage when driving inductive loads. This configuration provides a path for the inductive kickback current when the transistor turns off, protecting both the device and the driving circuitry.

Thermal Considerations

When operating multiple channels simultaneously or driving high currents, thermal management becomes important. The maximum power dissipation for the DIP package is 2.25 W and 1.4 W for the SOIC package. The thermal resistance (θ_JA) is approximately 60°C/W for the DIP package and 100°C/W for the SOIC package.

For continuous operation at maximum ratings, proper heat sinking or derating may be required. The power dissipation can be calculated using the formula:

P_D = V_CE(sat) × I_C × N

Where N is the number of active channels.

Pin Configuration

Pin 1-7: Inputs for channels 1-7
Pin 8: Ground
Pin 9: Common cathode for suppression diodes (COM)
Pin 10-16: Outputs for channels 1-7 (opposite corresponding inputs)

Design Considerations

When designing with the ULN2004A, several factors should be considered:

Ensure the COM pin (pin 9) is properly connected when driving inductive loads
For TTL compatibility, ensure input voltage meets TTL specifications
When driving multiple high-current loads simultaneously, consider thermal effects
For capacitive loads, include current-limiting resistors
Keep input leads short to minimize noise pickup
Use proper decoupling capacitors near the power pins

Reliability and Quality

The ULN2004A is manufactured with stringent quality control measures and is qualified to industry standards. The device undergoes multiple tests including: