STMicroelectronics L6221AD

Overview

L6221AD from STMicroelectronics is a monolithic quad Darlington switch IC designed for high-voltage, high-current switching of inductive loads. It integrates four non-inverting Darlington drivers with TTL-compatible inputs, common enable control, integral fast recirculation diodes, and a shared emitter configuration. Each channel supports up to 50 V output voltage and 1.8 A continuous collector current, with typical V_CE(sat) of 1.0 V at 0.6 A.

For engineers reviewing the L6221AD datasheet, L6221AD pinout, L6221AD application, or L6221AD equivalent, key selection criteria include its 1.8 A per-channel drive capability, 50 V sustaining voltage, low saturation voltage, integrated clamp diodes, and SO16+2+2 package thermal performance under industrial motor/solenoid switching conditions.

Technical Context

The L6221AD implements four independent open-collector NPN Darlington pairs, each with a dedicated fast freewheeling diode connected between collector and VS (logic supply). All inputs are TTL-compatible (V_INL ≤ 0.8 V, V_INH ≥ 2.0 V), and a single ENABLE pin controls all four channels simultaneously via active-high logic.

Its internal architecture features common-emitter topology with externally accessible emitter pins (pins 1, 9, 10, 17), enabling flexible paralleling of outputs. The device operates over −40 °C to +150 °C junction temperature and requires no external bias components for basic switching operation.

Key Specifications

Pinout & Package

E-L6221AD is housed in a 20-pin SO16+2+2 surface-mount package (20-lead small outline with two extra pins for thermal/ground enhancement), measuring 20.0 mm × 8.80 mm × 3.30 mm. Pin pitch is 2.54 mm, and the package complies with ECOPACK® environmental standards.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ULN2803A and TB6549FNG, the L6221AD uniquely balances per-channel current capacity (1.8 A), dual-group clamp diode architecture, and TTL compatibility in a 20-pin SO package-making it optimal for industrial solenoid banks where reliability, layout simplicity, and thermal margin are prioritized over channel density or advanced control features.

Availability

L6221AD is available at Aetrix Electronics and suitable for industrial solenoid control, PLC output stages, and DC motor direction logic requiring stable component supply and long-term manufacturability.

Supply support for L6221AD 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, specializing in power management, analog, microcontrollers, and automotive-grade ICs.

The L6221AD belongs to ST's high-voltage power driver product line, engineered specifically for robust industrial actuation-emphasizing ruggedness, integrated protection, and simplified system-level design for inductive load switching.

FAQ

What is the maximum allowable ambient temperature for continuous 1.8 A operation per channel?

At 1.8 A per channel and 70 °C ambient, the L6221AD in SO16+2+2 package dissipates approximately 3.24 W (1.8 A × 1.8 V). With R_{th j-amb} = 80 °C/W, junction temperature reaches 215 °C - exceeding the 150 °C limit. Derating is required: maximum ambient is 45 °C for full 1.8 A per channel, or use PCB copper heatsinking to reduce R_{th j-amb} per Figure 25.

Can CLAMP A and CLAMP B be connected to different supply rails?

No. CLAMP A and CLAMP B must both connect to the same VS rail (4.5–5.5 V). Connecting them to separate supplies violates the internal diode biasing scheme and risks latch-up or uncontrolled flyback paths. The datasheet specifies VS as the sole clamp reference, and Figure 19 shows both clamps tied to one VS node.

Is the L6221AD suitable for driving N-channel MOSFET gates?

No. The L6221AD is an open-collector Darlington output stage with limited peak current (2.5 A) and slow rise/fall times (2–5 μs). It lacks the gate charge drive capability, voltage headroom (>10 V), and fast edge rates needed for efficient MOSFET gate driving. Dedicated gate drivers like STGAP2SIC or IRS2007 should be used instead.

How should unused inputs be terminated?

Unused INx inputs must be tied to GND (not left floating) to prevent false triggering from noise. ENABLE must also be held low (GND) if the device is disabled. Floating inputs cause unpredictable output states and increased supply current due to partial transistor turn-on in the TTL input stage, as confirmed by I_INL = −100 μA leakage specification.