Microchip Technology AT43USB326-AU

Overview

AT43USB326-AU from Microchip Technology (formerly Atmel) is an 8-bit AVR RISC microcontroller integrating a USB 1.1 hub controller and embedded keyboard function. It delivers 12 MIPS throughput, features 16 KB masked ROM program memory, 512 bytes SRAM, 32 I/O pins, and supports up to 18×8 keyboard matrix scanning with four LED drivers. It operates at 5 V with on-chip 3.3 V USB power supply and targets USB peripheral controller applications in keyboards, kiosks, and human interface devices.

For engineers reviewing the AT43USB326-AU datasheet, AT43USB326-AU pinout, AT43USB326-AU application, or AT43USB326-AU equivalent, key selection considerations include its integrated USB hub + keyboard controller architecture, 48-lead LQFP package, 6 MHz crystal + PLL clocking, programmable endpoints (three total), and absence of UART/SPI/EEPROM - making it purpose-built for cost-sensitive, fixed-function HID hubs.

Technical Context

The AT43USB326-AU implements a compound USB device architecture: one permanently attached USB function (on Port 1) and two configurable downstream ports (Ports 2–3), all managed via firmware-defined hub descriptors. Its USB hardware includes dedicated registers mapped to SRAM ($1F00–$1FFF), separate interrupt vectors for USB events (e.g., vector $018), and dual endpoint control - Hub Endpoint 0 and Function Endpoints 0–2, each with 8-byte FIFOs.

Internally, it uses a Harvard architecture with single-cycle ALU execution, 32 general-purpose registers directly connected to the ALU, and a 13-bit program counter addressing 8K × 16-bit instructions. Clocking derives from a 6 MHz crystal with on-chip PLL generating the precise 12 MHz USB timing (±20.8 ns cycle deviation), meeting USB 1.1 hub accuracy requirements (>100 ppm stability).

Key Specifications

Pinout & Package

AT43USB326-AU is housed in a 48-lead LQFP package with exposed pad (no thermal pad designation in source). Pin functions are validated per Atmel document 3313D–USB–04/06, including dedicated USB differential pairs (DP0/DM0, DP2/DM2, DP3/DM3), keyboard row/column I/O (PC[0:7], PA[0:7], PB[0:7], PE[0:1]), LED drivers (PE[4:7]), and oscillator/PLL pins (XTAL1, XTAL2, LFT).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar USB keyboard controller applications.

Compared with AT90USB1287-AU and NUC123LD4AN0, the AT43USB326-AU provides unique hardware acceleration for keyboard matrix scanning and integrated USB hub functionality - reducing firmware overhead and enabling simpler, lower-cost HID peripheral designs where fixed-function operation is acceptable.

Availability

AT43USB326-AU is available at Aetrix Electronics and suitable for compact USB keyboards, industrial keypads, kiosk terminals, and gaming peripheral hubs requiring stable component supply and long-term production continuity.

Supply support for AT43USB326-AU 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

Microchip Technology acquired Atmel in 2016 and maintains legacy AVR product lines including the AT43USB326-AU. The company specializes in microcontrollers, analog, and Flash-IP solutions for embedded control.

The AT43USB326-AU belongs to Atmel's USB-enabled AVR microcontroller family, designed specifically for cost-optimized, fixed-function human interface devices requiring integrated USB hub and keyboard controller logic.

FAQ

What is the primary function of the AT43USB326-AU in a USB peripheral design?

The AT43USB326-AU serves as a single-chip USB compound device combining a 3-port USB 1.1 hub and an embedded keyboard controller. It manages upstream communication with the host, downstream device enumeration on Ports 2 and 3, and real-time scanning of up to 144-key (18×8) matrices - all while generating standard USB HID reports. Its fixed-function architecture eliminates the need for external hub ICs or keyboard MCUs in cost-sensitive HID applications.

Does the AT43USB326-AU support firmware updates in the field?

No, the AT43USB326-AU uses 16 KB of masked ROM for program memory, meaning firmware is factory-programmed and immutable after production. It does not include flash, EEPROM, or any mechanism for field updates. This design ensures firmware integrity and reduces cost but requires final firmware validation before manufacturing.

Can the AT43USB326-AU operate without an external crystal?

No - the AT43USB326-AU requires a 6 MHz parallel-resonant crystal connected to XTAL1/XTAL2 for USB timing compliance. Its on-chip PLL depends on this crystal to generate the precise 12 MHz clock needed for USB 1.1 data transmission (±100 ppm accuracy). External clock drive is possible only on XTAL1, but crystal operation is mandatory for production use.

How many USB endpoints does the AT43USB326-AU support, and what types are they?

The AT43USB326-AU supports three USB endpoints: one default control endpoint (Endpoint 0) for the hub, and two additional programmable endpoints (Endpoints 1 and 2) for the embedded keyboard function. Endpoints 1 and 2 can be configured as interrupt IN/OUT or bulk IN/OUT, each with an 8-byte FIFO - sufficient for standard HID keyboard reports and status updates.

What are the power supply requirements for the AT43USB326-AU?

The AT43USB326-AU operates from a single 5 V supply applied to VCC. It integrates two 3.3 V regulators (outputting 30 mA each) for internal circuitry and the USB 1.5 kΩ pull-up resistor. High-quality 2.2 µF ceramic capacitors must be placed on CEXT1 and CEXT2. GPIO pins must not source current beyond the on-chip regulator capacity - external 3.3 V supply is required if driving high-load peripherals.