STMicroelectronics L6221CD

Overview

L6221CD from STMicroelectronics is a monolithic quad Darlington switch IC designed for high-voltage, high-current inductive load control. It features four non-inverting TTL-compatible inputs, a common enable pin, 60 V output voltage rating, 1.8 A continuous per-channel collector current, and integrated fast recirculation diodes. It is used in industrial solenoid drivers, relay interface modules, and PLC output stages.

For engineers reviewing the L6221CD datasheet, L6221CD pinout, L6221CD application, or L6221CD equivalent, key selection criteria include channel count, clamp diode integration, SO16+2+2 thermal performance, and enable-controlled parallel operation capability for higher current drive.

Technical Context

The L6221CD implements four independent open-collector Darlington output stages with shared emitter (GND) and dual clamping networks (CLAMPA for channels 1–2, CLAMPB for channels 3–4). Each channel includes an integral fast freewheeling diode rated for 2.2 V forward drop at 2 A.

It operates with logic supply voltage (VS) up to 7 V and supports TTL-level input thresholds (V_INH ≥ 2 V, V_INL ≤ 0.8 V), enabling direct interfacing with microcontrollers and FPGA I/O. The enable input globally gates all four outputs with propagation delays of 2 ms (t_d(on)) and 5 µs (t_d(off)) under 10 Ω load conditions.

Key Specifications

Pinout & Package

The L6221CD is housed in a 16-pin SOIC package with two additional exposed thermal pads (+2+2 configuration), providing enhanced thermal dissipation over standard SO16. Pin 1 is located at the top-left corner adjacent to the index mark.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ULN2803ADW and TB6549FG, the L6221CD uniquely balances per-channel current (1.8 A), integrated clamp diodes with configurable zener clamping, and TTL simplicity-making it optimal for industrial solenoid and relay interfaces where robustness and minimal external components are prioritized.

Availability

L6221CD is available at Aetrix Electronics and suitable for industrial automation, programmable logic controller (PLC) output modules, and automated test equipment requiring stable component supply and long-term obsolescence management.

Supply support for L6221CD 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 automotive, industrial, and power discrete solutions with vertical manufacturing capabilities.

The L6221CD belongs to ST's high-voltage power driver product line, engineered specifically for ruggedized industrial control applications demanding reliable high-current sinking capability with integrated protection.

FAQ

What is the maximum allowable voltage on the CLAMPA and CLAMPB pins?

The CLAMPA and CLAMPB pins are anodes of internal clamp diodes connected to OUT1–OUT2 and OUT3–OUT4 respectively. Their voltage must not exceed 60 V above GND, as this is the absolute maximum output sustaining voltage. External zener diodes must be selected so that V_Z + V_F(diode) ≤ 60 V under worst-case temperature and tolerance conditions to prevent device damage.

Can multiple L6221CD outputs be paralleled, and what precautions apply?

Yes-channels 1 & 4 or 2 & 3 may be paralleled to increase current capacity to 3.6 A per pair. ST recommends this pairing due to matched propagation delays and saturation voltages. Ensure identical PCB trace lengths, shared GND plane, and simultaneous enable control. Do not parallel non-matching pairs (e.g., IN1 with IN3) as timing skew may cause current imbalance and thermal stress.

Is the L6221CD RoHS compliant and halogen-free?

Yes-the L6221CD is manufactured in accordance with STMicroelectronics' environmental policy and meets RoHS Directive 2011/65/EU requirements. Its SO16+2+2 package is also halogen-free and complies with JEDEC JS709A standards. Full material declarations and compliance certificates are available through ST's official product portal under document number CD00001371.

How does thermal performance differ between the L6221CD and L6221C Powerdip versions?

The L6221CD (SO16+2+2) achieves R_{th j-amb} ≈ 35 °C/W with 250 mm² copper pour, versus 80 °C/W for the Powerdip version at same ambient. The exposed thermal pads in the SO package allow direct conduction to inner-layer GND planes, improving power handling by ~2× at 70 °C ambient. Derating curves in the datasheet confirm 3.5 W max dissipation for L6221CD vs. 1 W for L6221C under identical board conditions.