Allegro MicroSystems A6278ELWTR-T

Overview

A6278ELWTR-T from Allegro MicroSystems is an 8-channel serial-input constant-current latched LED driver with open-LED detection, designed for microprocessor-controlled LED displays. It features Schmitt-trigger inputs, 3.0–5.5 V logic supply, up to 90 mA per output, and 20 ns output staggering delay. Used in industrial panel meters and signage where reliable LED current control and fault reporting are required.

For engineers reviewing the A6278ELWTR-T datasheet, A6278ELWTR-T pinout, A6278ELWTR-T application, or A6278ELWTR-T equivalent, this page delivers verified electrical parameters, SOICW package mapping, functional block context, real-world use cases, and two validated alternative parts with documented technical and application differences.

Technical Context

The A6278ELWTR-T integrates a CMOS shift register, parallel latches, and eight NPN constant-current sink drivers in a single SOICW-16 package. Its open-LED detection operates via V_CE threshold comparison (0.30 V typical) and reports faults serially through the SERIAL DATA OUT pin during dedicated test mode.

Internal UVLO (2.15–2.85 V trip range) and thermal shutdown (165 °C typical) ensure robust operation under supply transients and overload conditions. Output current is set externally via R_EXT, enabling precise per-bit current tuning across varying LED forward voltages (1.2–4.0 V) and load supply voltages up to 17 V.

Key Specifications

Pinout & Package

Package: 16-pin SOICW (suffix LW), lead-free with 100% matte tin plating; 7.5 mm × 10.3 mm body, 2.65 mm max height, exposed thermal pad not present (SOICW differs from TSSOP-LP/ET).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar constant-current LED driver applications.

Compared with A6278ELWTR-T, the A6279ELWTR-T offers double the channel count at the expense of larger footprint and higher supply current, while the TLC59282DBQR trades diagnostics and drive strength for lower cost and simpler thermal management - making each viable only within distinct design constraints.

Availability

A6278ELWTR-T is available at Aetrix Electronics and suitable for industrial panel meters, outdoor LED signage, and medical device status indicators requiring stable component supply and long-term production continuity.

Supply support for A6278ELWTR-T 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

Allegro MicroSystems designs high-performance magnetic sensors and power ICs for automotive, industrial, and consumer applications, with core expertise in precision analog and mixed-signal semiconductor solutions.

The A6278 product line targets LED display systems requiring integrated current regulation, fault diagnostics, and microprocessor-compatible serial control - emphasizing reliability in harsh environments and simplified system-level design.

FAQ

What is the maximum recommended load supply voltage (VLED) for the A6278ELWTR-T?

The A6278ELWTR-T supports a load supply voltage (VLED) range of –0.5 V to 17 V. However, to avoid excessive package power dissipation, VLED should be minimized using external voltage dropping components (e.g., series resistors or Zener diodes) so that V_CE remains ≤3 V. At 90 mA per channel and 8 active outputs, exceeding 5 V for VLED risks exceeding thermal limits in standard SOICW layouts without enhanced copper pour or thermal vias.

How does open-LED detection work on the A6278ELWTR-T, and how is the result read?

The A6278ELWTR-T performs open-LED detection by comparing each output's V_CE against a 0.30 V threshold during dedicated test mode. When enabled, it sets a '0' bit for open circuits and '1' for normal operation in its internal shift register. The result is read serially via the SERIAL DATA OUT pin after issuing three CLOCK pulses with OUTPUT ENABLE held low - a process fully documented in the A6278ELWTR-T datasheet timing diagrams.

Can the A6278ELWTR-T operate with a 3.3 V logic supply, and what is the minimum clock pulse width?

Yes, the A6278ELWTR-T operates across a 3.0–5.5 V logic supply range, fully supporting 3.3 V microcontrollers. The minimum CLOCK pulse width (both high and low periods) is 20 ns in normal mode, enabling reliable operation at up to 25 MHz serial data rates. Input hysteresis of 200–400 mV on all digital pins ensures noise immunity even with marginal signal integrity.

What is the purpose of the REXT pin on the A6278ELWTR-T, and how is output current calculated?

The REXT pin on the A6278ELWTR-T connects an external resistor that sets the constant-current sink value for all eight outputs. Output current is calculated as I_O ≈ 1.25 V / R_EXT, yielding 75.5 mA typical at R_EXT = 470 Ω and 40.0 mA at R_EXT = 3.9 kΩ. This single-resistor method ensures tight matching (±6% max difference between any two outputs) and eliminates per-channel calibration.

Does the A6278ELWTR-T include thermal protection, and how does it behave during shutdown?

Yes, the A6278ELWTR-T includes thermal shutdown (TSD) triggered at 165 °C typical junction temperature. During TSD, all output drivers disable while shift registers and latches retain their stored data. Once junction temperature falls below ~150 °C (15 °C hysteresis), outputs automatically resume operation with no reset required - preserving display state and avoiding visible flicker or corruption in A6278ELWTR-T-based systems.