Texas Instruments ULN2001AD

Overview

ULN2001AD from Texas Instruments is a 7-channel high-voltage, high-current NPN Darlington transistor array designed for low-side switching of inductive and resistive loads. It delivers 500mA per channel, supports 50V collector-emitter voltage, integrates input-compatible base resistors and common-cathode clamp diodes, and is used in relay control circuits within industrial PLC I/O modules.

For engineers reviewing the ULN2001AD datasheet, ULN2001AD pinout, ULN2001AD application, or ULN2001AD equivalent, key selection criteria include per-channel current capability, integrated flyback diode configuration, input logic compatibility (TTL/CMOS), thermal derating at elevated ambient temperatures, and SOIC-16 package footprint constraints.

Technical Context

The ULN2001AD implements seven independent Darlington pairs with internal 2.7kΩ series base resistors-enabling direct interface to 5V TTL and CMOS logic without external biasing. Each channel features an open-collector output and shares a common emitter (pin 8) and common cathode clamp diode node (pin 9).

It operates across –40°C to 70°C ambient temperature, with absolute maximum ratings of 50V V_CE, 500mA peak collector current per channel, and 2.5A total emitter current. Switching performance includes 0.25–1μs propagation delay (t_PLH/t_PHL) at 25°C, and V_CE(sat) ≤1.6V at I_C = 350mA and I_B = 500μA.

Key Specifications

Pinout & Package

ULN2001AD uses a 16-pin SOIC (D) package with 1.27mm pitch, 9.90mm × 3.91mm body size, and exposed pad not present. Pin 1 is top-left corner (dot-marked), with pins numbered counter-clockwise.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ULN2001AD, ULN2003AD offers broader logic voltage support and lower minimum operating temperature, while ULN2803AD adds channel count without altering thermal or layout constraints-both retain identical per-channel drive strength and clamp diode functionality.

Availability

ULN2001AD is available at Aetrix Electronics and suitable for industrial automation, automotive lamp control, and embedded motion control applications requiring stable component supply and long-term manufacturing continuity.

Supply support for ULN2001AD 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 for industrial, automotive, and communications markets.

The ULN200x family was engineered for robust, cost-effective interface between low-voltage logic and high-power electro-mechanical loads-targeting relay drivers, lamp controllers, and stepper motor systems in harsh environments.

FAQ

What is the maximum continuous current per channel for ULN2001AD?

The ULN2001AD supports 500mA continuous collector current per Darlington channel under recommended operating conditions (T_A ≤70°C, V_CE ≤50V). Derating is required above 70°C ambient-e.g., ~350mA at 85°C-based on R_θJA = 88.6°C/W and T_J(max) = 125°C. ULN2001AD must not exceed its absolute maximum rating of 500mA even at short durations.

Does ULN2001AD include built-in flyback diodes?

Yes, ULN2001AD integrates seven common-cathode clamp diodes-one per channel-connected between each collector output (pins 10–16) and the COM pin (pin 9). These diodes protect against inductive kickback when switching relays or motors; the COM pin must be connected to the positive side of the inductive load supply for proper operation.

Can ULN2001AD be used with 3.3V microcontroller GPIOs?

ULN2001AD is rated for TTL/5V CMOS compatibility but functions reliably with 3.3V logic inputs. At 3.3V, input current is ~1.2mA (via internal 2.7kΩ resistor), sufficient to saturate the Darlington pair for loads up to 300mA. For guaranteed 3.3V operation across temperature, TI recommends ULN2003AD-documented for 3.3V compatibility in its datasheet.

What is the purpose of the E pin (pin 8) on ULN2001AD?

Pin 8 (E) is the common emitter terminal shared by all seven Darlington pairs. It must be connected to system ground (0V reference) to complete the current path for all sink outputs. Leaving E floating disables all channels; tying E to ground ensures proper biasing and enables simultaneous or independent channel control via inputs 1B–7B and outputs 1C–7C.

How does ULN2001AD differ from ULN2003AD in practical use?

ULN2001AD and ULN2003AD share identical SOIC-16 packaging, pinout, 2.7kΩ input resistors, 500mA/50V ratings, and internal diode structure. The key distinction is documentation: ULN2003AD explicitly specifies 3.3V logic compatibility and –40°C to 70°C operation, whereas ULN2001AD datasheet references focus on 5V TTL and –20°C to 70°C. For new designs, ULN2003AD provides stronger assurance of low-voltage and low-temperature performance.