STMicroelectronics L6221AS

Overview

L6221AS from STMicroelectronics is a monolithic quad Darlington switch IC with four non-inverting TTL-compatible inputs, a common enable pin, and open-collector outputs rated for 50 V and 1.8 A per channel. It integrates fast recirculation diodes and features low saturation voltage (1.6 V at 1.8 A), making it suitable for driving inductive loads such as solenoids and relays in industrial control systems.

For engineers reviewing the L6221AS datasheet, L6221AS pinout, L6221AS application, or L6221AS equivalent, key selection criteria include output current capability per channel, integrated clamp diode performance, thermal resistance (R_{th j-pins} = 14 °C/W), and compatibility with 5 V logic interfaces in high-voltage switching designs.

Technical Context

The L6221AS implements four independent Darlington transistor stages sharing a common emitter node and dual clamp diode networks (CLAMP A/B), each protecting two adjacent channels during inductive load commutation. Its enable-controlled architecture allows synchronous activation of all four switches while maintaining individual input control.

Designed for direct interface with TTL/CMOS logic, it operates with logic supply voltage (VS) from 4.5 V to 5.5 V and supports peak collector currents up to 3.2 A (non-repetitive, 10 μs), with turn-on/off delays under 2 μs and 5 μs respectively into 10 Ω loads.

Key Specifications

Pinout & Package

E-L6221AS uses a 16-pin Power DIP (Dual In-line Package) with exposed thermal pad on the underside for enhanced thermal dissipation. Pin layout follows standard ST Power DIP footprint with GND pins positioned for optimal grounding and thermal conduction.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ULN2803A and TB6549FG, the L6221AS uniquely combines 1.8 A per channel, dual CLAMP terminals for Zener-tuned inductive decay, and matched channel pairing-making it optimal for high-reliability, high-current unidirectional actuator control where thermal and timing precision matter.

Availability

L6221AS is available at Aetrix Electronics and suitable for industrial PLC output modules, automated valve actuation systems, printer paper feed mechanisms, and test equipment relay drivers requiring stable component supply and long-term manufacturing continuity.

Supply support for L6221AS 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, mixed-signal, power, and microcontroller products for industrial, automotive, and consumer markets.

The L6221AS belongs to ST's high-voltage power driver product line, engineered specifically for robust, thermally efficient switching of inductive loads in harsh industrial environments with minimal external components.

FAQ

What is the maximum allowable junction temperature for continuous operation of the L6221AS?

The L6221AS has a specified operating junction temperature range of –40 °C to +150 °C. For reliable continuous operation, junction temperature must remain below +150 °C under worst-case ambient and power dissipation conditions, which requires proper PCB copper area or heatsink attachment per Figure 23 and Figure 24 in the datasheet.

Can multiple L6221AS outputs be paralleled to increase current capacity?

Yes - the datasheet explicitly recommends paralleling IN1/IN4 and IN2/IN3 due to closely matched electrical characteristics, enabling up to 3.6 A per pair. However, collectors must be placed close together on the PCB to avoid current imbalance at turn-off, and external Zener clamping must be applied per CLAMP A/B terminals.

Is the L6221AS RoHS-compliant and lead-free?

Yes - the E-L6221AS is offered in ST's ECOPACK® package, meeting RoHS Directive 2011/65/EU requirements. The device is lead-free, halogen-free, and complies with ST's environmental specifications as documented on www.st.com/ecopack.

How does the CLAMP A and CLAMP B functionality differ from standard freewheeling diodes?

CLAMP A and CLAMP B provide dedicated anode terminals for external Zener diodes, allowing programmable flyback voltage (e.g., V_Z + V_F) to accelerate inductive current decay. Unlike passive diodes, this configuration controls energy dissipation rate and reduces turn-off time - critical for high-speed solenoid or valve actuation.