Allegro MicroSystems A6277EA

Overview

A6277EA from Allegro MicroSystems is an 8-bit serial-input constant-current latched LED driver in a 20-pin DIP package, featuring eight NPN constant-current sink outputs (up to 150 mA per channel), CMOS shift register + latch architecture, and HIGH/LOW current-select function enabling 100% or 50% programmed current. It targets multiplexed LED display modules requiring precise current control and microprocessor interface.

For engineers reviewing the A6277EA datasheet, A6277EA pinout, A6277EA application, or A6277EA equivalent, key selection considerations include its 20 MHz max serial data rate at 5 V logic supply, user-programmable output current via single R_EXT, inter-digit blanking via active-low OUTPUT ENABLE, and thermal derating behavior across –40°C to +85°C ambient.

Technical Context

The A6277EA integrates a serial-shift register followed by parallel latches, allowing asynchronous data loading and synchronous output update on LATCH ENABLE high. Its BiCMOS design combines low-power CMOS logic with robust NPN sink drivers capable of 1.0 V saturation voltage at full load.

Current regulation is resistor-defined via terminal 19 (REXT), supporting programmable output currents from ~34 mA to 140 mA per channel depending on R_EXT value and V_CE. The dual serial data outputs (SDO1 on rising clock edge, SDO2 on falling edge) enable seamless cascading without external timing alignment.

Key Specifications

Pinout & Package

Package: 20-pin plastic DIP (suffix A), lead-free with 100% matte-tin plating, through-hole mount.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TD62715FN and CAT4016, the A6277EA offers higher per-channel current headroom (150 mA), resistor-based current tuning flexibility, and dual-edge serial outputs for deterministic cascading - making it optimal for demanding LED signage and automotive cluster applications where brightness consistency and thermal margin are critical.

Availability

A6277EA is available at Aetrix Electronics and suitable for LED matrix displays, industrial panel meters, automotive instrument clusters, and point-of-sale display modules requiring stable component supply and long-term industrial availability.

Supply support for A6277EA 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 and manufacturer of high-performance magnetic sensors, motor driver ICs, and precision power ICs, headquartered in Worcester, Massachusetts.

The A6277EA belongs to Allegro's constant-current LED driver product line, engineered specifically for high-reliability, thermally robust LED display systems in industrial and transportation environments.

FAQ

What is the maximum continuous output current per channel for the A6277EA at 85°C ambient?

The A6277EA can continuously sink 122 mA per output at 85°C ambient when mounted on a 1-layer PCB (R_θJA = 60°C/W), with V_CE ≤ 1.0 V. This rating is validated per Allegro's thermal derating curves and assumes proper PCB copper area and airflow. At lower ambient temperatures or with enhanced cooling, the A6277EA supports up to 150 mA per channel as specified in absolute maximum ratings.

How does the HIGH/LOW pin affect current regulation in the A6277EA?

The HIGH/LOW pin on the A6277EA provides hardware-selectable current scaling: a logic low applies 100% of the R_EXT-programmed current to all eight outputs, while a logic high reduces output current to 50% of that value. This function operates independently of the latches and OUTPUT ENABLE, enabling rapid brightness adjustment without reprogramming R_EXT or altering serial data flow - a feature unique to the A6277EA among its class.

Can the A6277EA be used with white or blue LEDs requiring forward voltages above 3.5 V?

Yes, the A6277EA supports white and blue LEDs (VF = 3.5–4.0 V) when paired with an external voltage dropper (e.g., Zener diode or series resistor) between the LED anode and supply rail. Because the A6277EA's V_CE is typically 0.4–0.7 V, minimizing total drop across the driver reduces package power dissipation - critical for maintaining thermal stability in high-VF LED applications using the A6277EA.

What is the purpose of separating LOGIC GROUND (pin 1) and POWER GROUND (pins 6 & 15) on the A6277EA?

The A6277EA separates LOGIC GROUND and POWER GROUND to prevent switching noise from high-current outputs from corrupting sensitive CMOS inputs (CLOCK, LATCH ENABLE, SERIAL DATA IN). If both grounds share a common trace with significant impedance, voltage spikes exceeding 2.5 V on logic inputs relative to system ground may cause mislatching or clock errors - a failure mode explicitly documented in the A6277EA application notes.

Is the A6277EA still in active production, and what is its obsolescence status?

The A6277EA variant is classified as LAST TIME BUY per Allegro's November 2009 notice: it remains available for existing customer applications but is obsolete for new designs, with final order deadline April 30, 2010. Aetrix Electronics maintains legacy inventory and supports continuity planning for ongoing production, but recommends evaluating alternatives like TD62715FN for new designs requiring long-term supply assurance.