STMicroelectronics L603C

Overview

L603C from STMicroelectronics is an 8-channel high-voltage Darlington array IC with open-collector outputs, common-emitter configuration, 400 mA continuous/500 mA peak per channel, 90 V V_CEX, integral clamp diodes, and TTL-compatible inputs. It drives inductive loads such as relays and solenoids in industrial control modules.

For engineers reviewing the L603C datasheet, L603C pinout, L603C application, or L603C equivalent, key selection criteria include output voltage rating (90 V), per-channel current capability (400 mA), integrated suppression diode presence, input logic compatibility (5 V TTL), and DIP-18 thermal resistance (70 °C/W).

Technical Context

The L603C integrates eight independent Darlington pairs sharing a common emitter connection per channel, each with a built-in reverse-biased clamp diode across collector–emitter to suppress inductive kickback. Input pins are arranged opposite output pins on the DIP-18 package to minimize PCB trace crossovers.

It operates with TTL-level input thresholds: V_i(ON) ≤ 2.5 V and V_i(OFF) ≥ 0.75 V at V_CE = 3 V and 90 V respectively. Saturation voltage is 1.2 V at I_C = 100 mA / I_B = 250 µA, supporting efficient switching of medium-power DC loads.

Key Specifications

Pinout & Package

DIP-18 plastic dual in-line package (23.24 mm × 8.5 mm, 2.54 mm pitch), through-hole mounting, JEDEC MS-001AC compliant. Thermal pad not present; power dissipation managed via PCB copper area and ambient convection.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ULN2803A and TB6549FG, the L603C uniquely combines 90 V blocking capability, integrated clamp diodes, and TTL input compatibility in a single DIP-18 package-making it irreplaceable for legacy 72 V industrial relay systems requiring minimal BOM count and layout simplicity.

Availability

L603C is available at Aetrix Electronics and suitable for industrial control systems, thermal printer manufacturing, and automated equipment requiring stable component supply with long-lifecycle support.

Supply support for L603C 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, designing and manufacturing analog, mixed-signal, power, and microcontroller products for industrial, automotive, and consumer markets.

The L603C belongs to ST's legacy high-voltage Darlington array product line, engineered specifically for robust, low-complexity interfacing between digital logic and medium-power inductive or resistive loads in factory automation hardware.

FAQ

Can L603C drive 72 V DC relays without external components?

Yes. Its 90 V V_CEX rating and integrated clamp diodes allow direct connection to 72 V relay coils. The diode anode connects to pin 18 (V_CC), which should be tied to the relay supply rail to absorb flyback energy. No external diodes or RC snubbers are required under normal switching conditions.

What is the maximum number of L603C outputs that can be safely paralleled?

Up to four outputs may be paralleled per logical channel, yielding 1.6 A continuous current (4 × 400 mA), provided thermal derating is applied. Total package power must remain ≤1.8 W; at 1.6 A and 1.2 V V_CE(sat), dissipation reaches ~1.92 W - thus forced-air cooling or reduced duty cycle is required beyond three paralleled channels.

Does L603C require a base resistor on its inputs?

No. Internal input resistors (2.7 kΩ, 7.2 kΩ, and 3 kΩ networks per channel) provide proper current limiting and logic-level translation. Direct connection to 5 V TTL outputs is safe; no external series resistor is needed, simplifying interface design and reducing component count.

How does L603C differ from L604C in practical use?

L604C uses CMOS-compatible inputs (6–15 V logic high), while L603C is optimized for 5 V TTL (≤2.5 V logic high). Their output stages, clamp diodes, and package are identical. Use L603C with microcontrollers and 5 V logic families; choose L604C when interfacing with 12 V industrial PLC outputs or analog comparator thresholds.