Allegro MicroSystems A6277EA-T

Overview

A6277EA-T from Allegro MicroSystems is an 8-bit serial-input constant-current latched LED driver with NPN sink outputs, designed for multiplexed LED display systems. It integrates a CMOS shift register, data latches, and eight 150 mA-rated constant-current drivers, supporting up to 20 MHz serial data input at 5 V logic supply and enabling inter-digit blanking via ENABLE control.

For engineers reviewing the A6277EA-T datasheet, A6277EA-T pinout, A6277EA-T application, or A6277EA-T equivalent, key selection considerations include its 20-pin DIP package, user-programmable output current via R_EXT, HIGH/LOW current scaling (100% or 50%), undervoltage lockout, and cascade-capable dual serial data outputs (SDO1/SDO2).

Technical Context

The A6277EA-T implements a serial-to-parallel architecture where rising-edge clock shifts data into an 8-bit shift register, and a high-level LATCH ENABLE transfers contents to independent output latches-enabling continuous data loading while holding stable outputs. Its dual serial outputs (SDO1 on rising edge, SDO2 on falling edge) support daisy-chained configurations without external logic.

Output current is set by a single external resistor (REXT) connected to pin 19, establishing identical sink current across all eight outputs; the HIGH/LOW input (pin 5) provides hardware-selectable 100% or 50% current scaling per bit, while OUTPUT ENABLE (pin 16, active-low) globally blanks all outputs with no effect on latch state.

Key Specifications

Pinout & Package

20-pin through-hole DIP (suffix A), Pb-free with 100% matte-tin leadframe plating. Copper leadframe enables high thermal performance and continuous 122 mA total sink current over –40°C to +85°C.

Key Features

Applications

Equivalent & Alternatives

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

Compared with A6277EA-T, TD62715FN offers identical pinout and current programming but omits undervoltage lockout, while CAT4016 trades channel count and package size for reduced current capability and loss of hardware current scaling - making A6277EA-T optimal for robust, high-current, multiplexed LED displays requiring thermal stability and simple brightness control.

Availability

A6277EA-T is available at Aetrix Electronics and suitable for LED segment displays, dot-matrix panels, bar graphs, and industrial annunciator systems requiring stable component supply and long-term design continuity.

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

The A6277 product line targets LED display systems requiring reliable, thermally robust constant-current driving with minimal microcontroller resource usage - emphasizing latch retention, daisy-chain scalability, and hardware-based current control.

FAQ

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

The A6277EA-T delivers up to 122 mA total sink current across all eight outputs continuously at 85°C ambient when mounted on a 1-layer PCB (R_θJA = 60°C/W). Per-channel current depends on duty cycle and V_CE; at 100% duty and V_CE = 1.0 V, individual outputs sustain 150 mA - verified in Allegro's thermal characterization data for the DIP package.

How does the HIGH/LOW pin on A6277EA-T affect LED brightness control?

The HIGH/LOW pin (pin 5) on A6277EA-T provides hardware-selectable current scaling: a logic low enables 100% of the R_EXT-programmed current per output, while a logic high reduces it to 50%. This enables coarse brightness adjustment without PWM timing overhead or firmware intervention - ideal for static display intensity tuning in industrial HMIs.

Can A6277EA-T be cascaded with other A6277EA-T devices, and how is data synchronized?

Yes, A6277EA-T supports daisy-chaining via two dedicated serial outputs: SDO1 (pin 18, triggered on clock rising edge) and SDO2 (pin 17, triggered on clock falling edge). This dual-edge architecture ensures deterministic, skew-free data propagation across multiple A6277EA-T devices - eliminating timing jitter in large LED arrays requiring synchronized column updates.

What is the role of separate LOGIC GROUND and POWER GROUND pins on A6277EA-T?

A6277EA-T uses isolated LOGIC GROUND (pin 1) and POWER GROUND (pins 6 and 15) to prevent switching noise from high-current LED sinks from corrupting digital inputs (CLOCK, LATCH ENABLE, etc.). If shared, voltage spikes exceeding 2.5 V between system ground and control pins may cause mislatching - proper PCB layout with separate ground planes is mandatory for reliable A6277EA-T operation.

Does A6277EA-T include built-in protection features beyond undervoltage lockout?

Yes, A6277EA-T incorporates Class 2 input static protection on all logic pins, safeguarding against ESD events up to ±2 kV (HBM). While not featuring overtemperature shutdown, its thermal derating curves (provided in Allegro's datasheet Figure GP-062) define safe operating current limits across ambient temperature and duty cycle - enabling robust design without external thermal monitoring.