Microchip Technology 25AA640AX-I/ST

Overview

25AA640AX-I/ST from Microchip Technology Inc. is a 64-Kbit SPI Serial EEPROM with 8192 × 8-bit organization, 32-byte page size, and 1.8V–5.5V supply range. It supports up to 10 MHz clock (at V_CC ≥ 4.5V), features hardware write protection via WP pin and STATUS register, and operates across industrial temperature range (−40°C to +85°C) in an 8-lead SOIC package. Used for nonvolatile configuration storage in microcontroller-based systems.

For engineers reviewing the 25AA640AX-I/ST datasheet, 25AA640AX-I/ST pinout, 25AA640AX-I/ST application, or 25AA640AX-I/ST equivalent, key selection criteria include SPI interface compatibility, 1 µA standby current at 5.5V/85°C, 1M endurance cycles, block-level write protection (none/¼/½/all), and AEC-Q100-qualified variants for automotive use.

Technical Context

The 25AA640AX-I/ST implements a standard SPI Mode 0,0/Master-Slave interface with separate SI (data-in) and SO (data-out) lines, controlled by CS, SCK, and HOLD. Its internal architecture includes a 32-byte page latch, HV generator for EEPROM programming, and status register with WIP, WEL, BP0/BP1, and WPEN bits.

Write operations require explicit WREN instruction before WRITE or WRSR, and automatic write-cycle termination occurs on CS high after final data bit. HOLD pin suspends ongoing transfers without resetting sequence state, enabling host interrupt servicing while preserving address pointer and command context.

Key Specifications

Pinout & Package

8-Lead SOIC (SN) package, 3.90 mm body width, JEDEC MS-012AC compliant. Pin 1 marked with notch or dot; lead finish is matte tin (Pb-free).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar serial EEPROM applications.

Compared with 25LC640AT-I/ST, the 25AA640AX-I/ST supports lower-voltage operation down to 1.8V, making it suitable for energy-harvesting or ultra-low-power systems; compared with AT25DF641A-SHN-T, it offers simpler SPI protocol, integrated hardware write protection, and direct drop-in replacement for legacy 25XX640A designs.

Availability

25AA640AX-I/ST is available at Aetrix Electronics and suitable for industrial sensor calibration, medical device configuration, and automotive body control modules requiring stable component supply, long-term lifecycle support, and AEC-Q100-qualified reliability.

Supply support for 25AA640AX-I/ST 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 Inc. is a leading provider of microcontrollers, analog devices, and memory solutions, headquartered in Chandler, Arizona, with global design and manufacturing operations.

The 25AA640A family delivers cost-effective, low-power SPI EEPROMs optimized for configuration storage in resource-constrained embedded systems, emphasizing robustness, wide voltage operation, and automotive-grade reliability.

FAQ

What is the maximum SPI clock frequency supported by the 25AA640AX-I/ST?

The 25AA640AX-I/ST supports up to 10 MHz clock frequency when V_CC is 4.5V to 5.5V, 5 MHz at 2.5V to <4.5V, and 3 MHz at 1.8V to <2.5V. These AC timing limits are specified in Table 1-2 of the DS20001830G datasheet and directly impact achievable read/write throughput. The 25AA640AX-I/ST must be operated within these voltage-dependent frequency bounds to ensure reliable communication.

Does the 25AA640AX-I/ST require external pull-up resistors on its SPI lines?

No, the 25AA640AX-I/ST does not require external pull-ups on SI, SO, SCK, or CS - all inputs have internal weak pull-downs, and SO is actively driven or tri-stated. However, WP and HOLD are CMOS inputs with no internal bias; external pull-ups (typically 10 kΩ) are recommended if those pins are not actively driven to avoid floating states that could cause unintended write protection or hold activation in the 25AA640AX-I/ST.

How does the page write limitation affect firmware design for the 25AA640AX-I/ST?

The 25AA640AX-I/ST enforces a strict 32-byte page boundary: writing across a page boundary causes data to wrap within the same page instead of advancing to the next. Firmware must calculate destination address modulo 32 and split multi-byte writes at page edges. This constraint applies to all WRITE commands and is independent of the number of bytes being written - even two bytes crossing 0x001F→0x0020 will wrap to 0x0000 in the 25AA640AX-I/ST.

Can the 25AA640AX-I/ST be used in automotive applications?

Yes - the 25AA640AX-I/ST is explicitly qualified to AEC-Q100 Grade 3 (−40°C to +125°C ambient), and its industrial temperature grade (−40°C to +85°C) covers most cabin and non-engine-bay automotive use cases. The part marking "X-I/ST" confirms industrial temp and SOIC packaging; for extended temp, Microchip offers the 25AA640A-E/ST variant. All electrical and reliability specs in the 25AA640AX-I/ST datasheet apply to automotive deployment.

What happens to the write enable latch during a power cycle of the 25AA640AX-I/ST?

On power-up, the 25AA640AX-I/ST automatically resets the write enable latch (WEL = 0), disabling all write operations until a WREN instruction is issued. This behavior is hardwired and ensures no spurious writes occur during power ramp-up or brown-out conditions. The latch remains reset until the host explicitly clocks WREN (0000 0110) with CS low and proper SCK timing - a fundamental safety feature built into the 25AA640AX-I/ST's power-on state.