Allegro MicroSystems A6278EA-T

Overview

A6278EA-T from Allegro MicroSystems is an 8-channel serial-input constant-current latched LED driver with open-LED detection, designed for multiplexed LED display systems. It integrates a CMOS shift register, data latches, and NPN sink drivers, operates from 3.0–5.5 V logic supply, delivers up to 90 mA per output, and supports 25 MHz serial data input for microprocessor interfacing in signage and panel displays.

For engineers reviewing the A6278EA-T datasheet, A6278EA-T pinout, A6278EA-T application, or A6278EA-T equivalent, key selection criteria include its 16-pin DIP package, open-circuit fault reporting via SERIAL DATA OUT, user-adjustable current via R_EXT, and thermal shutdown protection at 165°C.

Technical Context

The A6278EA-T implements a serial-to-parallel conversion architecture using a 8-bit CMOS shift register and independent latches, enabling direct microcontroller control without external logic. Its constant-current sink outputs are set by a single external resistor (REXT), with matching tolerance ≤ ±6% across channels and 20 ns typical staggering delay to reduce EMI and ground bounce.

Open-LED detection operates in dedicated test mode: after initialization via OUTPUT ENABLE and LATCH ENABLE sequencing, it compares each output's V_CE against 0.30 V threshold and shifts error bits out via SERIAL DATA OUT. Internal UVLO (2.4–2.85 V) and thermal shutdown (165°C, 15°C hysteresis) ensure robust operation under supply or thermal stress.

Key Specifications

Pinout & Package

Package: 16-pin DIP (Package Type A), lead-free with 100% matte tin plating, 0.300" wide body, through-hole mounting.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TLC59282DBQR and MAX7219CWG+, the A6278EA-T uniquely combines 8-channel constant-current sinking, open-LED detection with serial readback, and user-defined current via R_EXT - making it optimal for diagnostic-capable, microcontroller-driven LED signage where reliability and serviceability are critical.

Availability

A6278EA-T is available at Aetrix Electronics and suitable for indoor LED signage, industrial panel displays, point-of-sale terminals, and transportation annunciators requiring stable component supply and long-term production continuity.

Supply support for A6278EA-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 is a U.S.-based designer of high-performance magnetic sensors and power ICs, founded in 1989 and headquartered in Worcester, Massachusetts.

The A6278 family was developed specifically for LED display systems requiring integrated fault detection, programmable current, and microprocessor-compatible serial control - targeting signage, instrumentation, and human-machine interface applications.

FAQ

What is the maximum allowable output current per channel for the A6278EA-T?

The A6278EA-T supports up to 90 mA per output channel when configured with appropriate R_EXT (e.g., 225 Ω) and within thermal limits. At 25°C ambient and 5 V V_DD, typical current is 75.5 mA with R_EXT = 225 Ω. Derating applies per duty cycle and ambient temperature - see Figure 11 for A6278-specific IO vs. DC curves. The A6278EA-T maintains this rating across its full operating temperature range (–40°C to +85°C).

How does open-LED detection work on the A6278EA-T?

The A6278EA-T performs open-LED detection in a dedicated test mode initiated by specific OUTPUT ENABLE and LATCH ENABLE timing sequences. During testing, each output's V_CE is compared to a 0.30 V threshold; results are encoded as error bits (0 = open/TSD, 1 = normal) and shifted out via SERIAL DATA OUT. The A6278EA-T requires no external components for this function, and error reporting occurs without interrupting normal display operation.

Can the A6278EA-T be used in cascade configuration with other A6278EA-T devices?

Yes, the A6278EA-T supports daisy-chaining via its CMOS SERIAL DATA OUT pin, which connects directly to the SERIAL DATA IN of the next device. This enables expansion beyond 8 outputs while retaining single-microcontroller control. Cascading preserves open-LED detection capability - error bits from all devices in the chain appear sequentially on the final device's SERIAL DATA OUT, allowing centralized fault diagnosis across large LED arrays.

What is the purpose of the REXT pin on the A6278EA-T?

The REXT pin on the A6278EA-T connects to an external resistor to ground, establishing the reference current for all eight output drivers. The relationship is inverse: lower R_EXT yields higher current (e.g., 225 Ω → ~75 mA), higher R_EXT yields lower current (e.g., 3900 Ω → ~5 mA). This single-resistor method ensures matched current across all channels and eliminates per-channel calibration - a core design feature of the A6278EA-T.

Does the A6278EA-T include thermal protection, and how does it behave?

Yes, the A6278EA-T incorporates thermal shutdown (TSD) that activates at 165°C junction temperature (typical), turning off all output drivers until the die cools to ~150°C (15°C hysteresis). Critically, the shift register and latches remain powered and retain their data during TSD events - ensuring display state integrity upon recovery. This behavior is documented in the A6278EA-T functional description and distinguishes it from drivers that reset on thermal fault.