ATMEGA325A-AU - AVR 8-bit MCU 32KB Flash 20MHz 64TQFP | Microchip
MPN: ATMEGA325A-AU β Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $4.52 | $4.52 |
| 10 | $4.1 | $41.00 |
| 100 | $3.72 | $372.00 |
| 500 | $3.4 | $1,700.00 |
| 1,000 | $3.12 | $3,120.00 |
ATMEGA325A-AU Overview
An 8-bit AVR microcontroller is a single-chip computer built around the Harvard-architecture AVR RISC core, in which program memory and data memory use separate buses, allowing most of its 131 powerful instructions to execute in a single clock cycle. Within the semiconductor hierarchy it sits below general-purpose microprocessors and above simple logic ICs, serving as the complete processing element in embedded power management, control, and human-interface systems.
Key features include the 20 MHz AVR core delivering up to 20 MIPS throughput, read-while-write ISP Flash for field firmware updates, 1 KB of non-volatile EEPROM for calibration data retention through power cycles, and 54 general-purpose I/O lines per the Microchip product page. A JTAG interface (JTA per Microchip) supports on-chip debugging and boundary-scan testing, and 32 general-purpose working registers give the compiler direct register access that keeps interrupt latency low.
Technically, the ATmega325A is the process-migrated A-variant of the original ATmega325: according to the Microchip application note AVR540, the A-version is a functionally identical, drop-in replacement for the ATmega325, qualification-tested identically, with minor electrical characteristic differences due to the new fabrication process. The AVR architecture combines single-cycle ALU operation with a two-stage pipeline, which is why the effective MIPS rating equals the clock frequency in MHz.
Typical applications include industrial control panels and automation nodes, metering and instrumentation front ends, and embedded systems that need dependable 5 V operation across wide temperature ranges.
For design, remember that the full 20 MHz speed grade applies at the higher supply voltage range; derate the maximum clock when operating at reduced VCC, and budget EEPROM endurance for data that changes frequently.
This page synthesizes distributor listings, the Microchip AVR540 migration note, drop-in family alternatives, and practical design guidance not found on standard datasheet pages.
Drop-in alternatives for ATMEGA325A-AU β same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with ATMEGA325A-AU (same form factor and footprint) β differing in Package, RoHS Status, Flash Memory, Number of I/O, Instruction Set.
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
ATMEGA3250P-20AU
β Drop-In β οΈ εζ°εΎ ιͺθ―β In Stock
$1.8 / Unit
View Datasheet βATMEGA3250PA-AUR
β Drop-In β οΈ εζ°εΎ ιͺθ―β In Stock
$2.98 / Unit
View Datasheet βATMEGA325-16MI
β Drop-Inβ In Stock
$3.05 / Unit
View Datasheet βATMEGA3250-16AU
β Drop-In β οΈ εζ°εΎ ιͺθ―β In Stock
$5.74 / Unit
View Datasheet βATMEGA329A-AU
β Drop-Inβ In Stock
$3.31 / Unit
View Datasheet βATMEGA329PA-AU
β Drop-Inπ Reference alternative (not in catalog)
ATMEGA325A-AU Maximum Ratings & Electrical Characteristics
| Core Architecture | 8-bit AVR RISC |
| Flash Memory | 32 KB (16K x 16) ISP Flash with read-while-write |
| SRAM | 2 KB |
| EEPROM | 1 KB |
| Maximum Clock Frequency | 20 MHz |
| Instructions | 131 powerful instructions, most single-cycle |
| General Purpose I/O | 54 lines |
| Working Registers | 32 general purpose registers |
| Debug / Test Interface | JTAG (on-chip debug and boundary scan) |
| Supply Voltage | 4.5 V to 5.5 V |
| Package | 64-TQFP, 14 x 14 mm, 0.8 mm pitch |
| Mounting Type | Surface Mount |
| Temperature Grade | Industrial |
| RoHS Status | Green (lead-free, per FindIC listing) |
| Lifecycle Stage | ACTIVE |
ATMEGA325A-AU 64-tqfp, 14 x 14 mm, 0.8 mm pitch Pin Configuration Guide
Pin configuration for ATMEGA325A-AU (64-tqfp, 14 x 14 mm, 0.8 mm pitch package). This digital IC includes GPIO, communication interfaces (UART, SPI, I2C), and power pins. Refer to the manufacturer datasheet for alternate pin functions and configuration options. Essential for embedded system design and PCB layout.
No detailed pinout data available for ATMEGA325A-AU.
Refer to the datasheet for full pin configuration.
Typical Applications
ATMEGA325A-AU is suitable for 6 applications: Industrial Control Panels, Metering and Instrumentation, Human-Machine Interface Controllers, Embedded Networking Nodes, Motor and Actuator Control, Legacy 5V System Redesign and Migration.
Industrial Control Panels
The ATMEGA325A-AU fits industrial control panels because its 54 GPIO lines directly drive keypads, LED banks, relays, and limit-switch inputs without port expanders, and its 4.5 V to 5.5 V supply connects natively to legacy 5 V industrial logic and sensor rails. The 20 MHz AVR core executes the 131-instruction RISC set mostly in single cycles, keeping scan loops for dozens of I/O points fast and deterministic. In a typical panel the MCU reads discrete inputs, debounces them in software, and drives relay outputs, while the 1 KB EEPROM stores configuration and trip counters across power cycles. JTAG boundary-scan supports production board test, a practical advantage in industrial certification workflows.
Recommended
Metering and Instrumentation
In energy meters and bench instrumentation, the ATMEGA325A-AU offers the combination of 1 KB EEPROM for calibration constants, a 32 KB Flash code space for measurement algorithms, and industrial temperature qualification, all in a 0.8 mm pitch 64-TQFP that assembles reliably on standard SMT lines. The 20 MHz core provides enough headroom for fixed-point DSP-style accumulation of sensor samples, while read-while-write Flash lets the device log events to program memory between measurements. Because calibration data must survive unpowered storage for years, the EEPROM's non-volatile retention is the deciding parameter over Flash-only MCUs; budget write endurance per the datasheet when calibration intervals are short.
Recommended
Human-Machine Interface Controllers
HMI boards with many buttons, encoders, and indicator LEDs benefit from the ATMEGA325A-AU's 54 GPIO and 32 working registers, which allow the compiler to keep scanning state in registers and minimize interrupt latency during simultaneous key events. The 20 MHz clock supports software-multiplexed LED driving at flicker-free refresh rates, and the JTAG port enables on-chip debugging of state-machine code directly on the assembled board. Firmware lives in the 32 KB read-while-write Flash, so menus and localization strings can be field-updated through ISP without removing the MCU. Designs that later need an integrated segment LCD can migrate to the pin-compatible ATMEGA329A family in the same footprint.
Recommended
Embedded Networking Nodes
For RS-485, CAN-bridge, or Modbus-style field nodes, the ATMEGA325A-AU supplies the serial-capable GPIO matrix and 2 KB SRAM needed for buffered protocol frames, while its 5 V I/O drives industrial transceivers directly without level shifting. The 20 MHz AVR core runs protocol stacks in C with headroom for CRC computation, and the 1 KB EEPROM stores node addresses and network parameters through power loss. JTAG simplifies firmware bring-up in dense backplane environments where test-point access is limited. Communication transceivers should be chosen for 5 V logic compatibility; placing the MCU between the transceiver and the field bus keeps the signal chain simple and robust in electrically noisy cabinets.
Recommended
Motor and Actuator Control
The ATMEGA325A-AU suits small motor and actuator controllers: its timers generate PWM for H-bridge drivers, the 20 MHz core closes control loops fast enough for DC and stepper motors, and abundant GPIO handles limit switches, encoders, and fault inputs simultaneously. The 4.5 V to 5.5 V operating range matches standard gate-driver logic thresholds, simplifying the interface between MCU and power stage. Industrial temperature qualification allows mounting inside actuator housings that see wide ambient swings. For safety, use the EEPROM to store last-known actuator position so the controller can resume gracefully after brownouts, and derate clock frequency per the AVR voltage-frequency curve if the supply rail droops under motor inrush current.
Recommended
Legacy 5V System Redesign and Migration
When maintaining legacy boards built around the original ATmega325, the ATMEGA325A-AU is the sanctioned migration path: Microchip application note AVR540 states the A-variant is a functionally identical, drop-in replacement for the ATmega325, qualified through the identical production test flow. Engineers can respin an aging board by simply placing the A-variant in the existing 64-TQFP footprint, keeping the schematic, layout, and programming fixtures unchanged. The only engineering task is reviewing AVR540's electrical-characteristic deltas, such as minor shifts in current consumption, and re-running system-level validation. This makes the part a low-risk BOM choice for extending the life of 5 V industrial products with long service commitments.
Recommended
Recommended Products Summary
Engineering reference data for ATMEGA325A-AU β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | ATMEGA3250P-20AU | ATMEGA3250PA-AUR | ATMEGA325-16MI | ATMEGA329A-AU |
|---|---|---|---|---|---|
| Package | 64-TQFP (14 x 14 mm, 0.8 mm pitch) | 64-TQFP (14 x 14 mm) - same footprint | 64-TQFP (14 x 14 mm) - same footprint | 64-TQFP (14 x 14 mm) - same footprint | 64-TQFP (14 x 14 mm) - same footprint |
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
| Flash Memory | 32 KB ISP Flash | 32 KB | 32 KB | 32 KB | 32 KB |
| SRAM | 2 KB | 2 KB | 2 KB | 2 KB | 2 KB |
| Max Clock Frequency | 20 MHz | 20 MHz | 20 MHz | 16 MHz | 20 MHz |
| General Purpose I/O | 54 lines | 69 lines | 69 lines | 54 lines | Reduced (LCD-shared ports) |
| LCD Driver | No | No | No | No | Yes (segment LCD) |
| Low Power Technology | Standard AVR (A-process) | picoPower | picoPower (PA) | Standard | Standard (A-process) |
| Drop-in on ATMEGA325A-AU Footprint | - | Yes (verify port mapping) | Yes (verify port mapping) | Yes (AVR540-documented migration) | Yes (LCD pins differ) |
Key Differentiators
- Maximum 54 GPIO among direct family peers at 20 MHz (vs ATMEGA329A-AU)
- 20 MHz speed grade vs legacy 16 MHz parts (vs ATMEGA325-16MI)
- Standard-process cost advantage over picoPower variants (vs ATMEGA3250PA-AUR)
Design Notes
The ATMEGA325A-AU operates from 4.5 V to 5.5 V, and its 20 MHz speed grade is valid only at the upper end of the supply range. Per the standard AVR frequency-versus-voltage curve, derate the maximum clock if the rail can sag toward 4.5 V under load transients; otherwise the core may violate timing. Decouple VCC with 100 nF ceramic capacitors at each supply pin pair plus a bulk 10 uF, placed within a few millimeters of the pins. Estimate: at 20 MHz with moderate I/O loading, expect active current in the tens of mA class per AVR family norms - confirm the exact figure from the manufacturer datasheet electrical characteristics table rather than assuming.
The 64-TQFP has a 0.8 mm pitch; use non-solder-mask-defined pads with the IPC-recommended toe/heel extensions for reliable reflow and inspection. Route the JTAG (TCK/TMS/TDO/TDI) traces as a short, matched group to a test header, since boundary-scan value is lost if the chain is unreliable. Keep the XTAL circuit tight: crystals for the 20 MHz main clock should sit adjacent to XTAL1/XTAL2 with short ground returns, and analog references should be filtered per the datasheet ADC section. Provide a solid ground plane under the entire 14 x 14 mm body to control return paths for the many simultaneous-switching GPIO.
A frequent migration error is assuming all 64-TQFP ATmega variants have identical port functions: the ATMEGA329A family shares package pins with its segment LCD driver, so a PCB designed for ATMEGA325A-AU GPIO on those pins will misbehave if a 329-series part is substituted. Always re-verify the datasheet pin table before alternate sourcing. Second pitfall: EEPROM writes during interrupt-heavy code - enforce a timed write sequence and allow the datasheet-specified write cycle time before power-down, or use brown-out detection to hold the device in reset while VCC decays, protecting EEPROM content integrity.
With up to 54 GPIO switching at up to 20 MHz, the ATMEGA325A-AU can generate significant conducted and radiated emissions in industrial enclosures. Reduce series output impedance by configuring unused pins as inputs with internal pull-ups, add 22-100 ohm series resistors on long ribbon-cable and keypad runs to slow edge rates, and stagger port updates in firmware rather than writing entire ports in single cycles. For boards requiring EMC certification, follow the JTAG and crystal routing discipline above and reserve board area for common-mode chokes on any cables leaving the enclosure.
Compliance Information
FindIC listing identifies the ATMEGA325A-AU as a Green part, indicating lead-free RoHS-compliant packaging. REACH, halogen-free, and conflict-minerals declarations should be requested from Microchip directly; not found in provided data.
