Microchip Technology 25AA256X-I/ST

Overview

25AA256X-I/ST from Microchip Technology is a 256 Kbit SPI Serial EEPROM with 32,768 × 8-bit organization, 64-byte page size, and 1.8–5.5 V supply range. It supports up to 10 MHz clock frequency, features hardware write protection via WP pin and STATUS register, and delivers 1 million erase/write cycles with >200-year data retention - deployed in industrial control modules for nonvolatile parameter storage.

For engineers reviewing the 25AA256X-I/ST datasheet, 25AA256X-I/ST pinout, 25AA256X-I/ST application, or 25AA256X-I/ST equivalent, key selection criteria include its 1.8 V minimum operating voltage, HOLD pin support for interrupt-safe SPI pausing, block-level write protection (0/¼/½/all array), and TSSOP-8 packaging suitable for space-constrained industrial PCBs.

Technical Context

The 25AA256X-I/ST implements a standard SPI Mode 0,0/Multi-Master-compatible serial interface with separate SI (data in) and SO (data out) lines, requiring only CS, SCK, SI, SO, WP, HOLD, VCC, and VSS. Its internal architecture includes an 8-bit instruction register, page latches, HV generator, and EEPROM array with automatic address incrementing during sequential reads.

Write operations require explicit WREN instruction followed by CS high-to-low transition to initiate self-timed internal write cycle (≤5 ms); the STATUS register provides real-time WIP and WEL status, while BP0/BP1 bits enable configurable block protection without firmware overhead.

Key Specifications

Pinout & Package

25AA256X-I/ST is housed in an 8-lead TSSOP package (4.4 mm body width), RoHS-compliant, with gull-wing leads and JEDEC-standard footprint. Pin 1 is marked via notch or dot; orientation follows standard TSSOP convention (pin 1 top-left, counterclockwise).

Key Features

Applications

Equivalent & Alternatives

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

Compared with 25LC256-I/ST, the 25AA256X-I/ST enables lower-voltage operation critical for energy harvesting systems, while AT25DF256A-SSH-T offers higher density and speed at the cost of command incompatibility and reduced endurance - making 25AA256X-I/ST optimal for reliable, low-power configuration storage.

Availability

25AA256X-I/ST is available at Aetrix Electronics and suitable for industrial PLCs, automotive ECUs, medical device configuration storage, and smart meter firmware parameter retention requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for 25AA256X-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 25AA256X-I/ST belongs to Microchip's serial EEPROM product line, engineered for robust, low-power nonvolatile storage in industrial, automotive, and medical applications where data integrity and long-term reliability are mandatory.

FAQ

What is the minimum supply voltage required for reliable operation of the 25AA256X-I/ST?

The 25AA256X-I/ST operates reliably down to 1.8 V across its full industrial temperature range (-40°C to +85°C). This enables direct integration into battery-powered or energy-harvesting systems where rail voltages dip below 2.5 V. Below 1.8 V, read/write functionality is not guaranteed per datasheet specifications, and the device may enter undefined states. Always verify VCC stability during brown-out conditions using the built-in power-on reset circuitry.

Does the 25AA256X-I/ST support SPI Mode 1,1 or only Mode 0,0?

The 25AA256X-I/ST supports SPI Mode 0,0 exclusively - sample on rising clock edge, output on falling edge, with clock idle low. It does not support Mode 1,1 (clock idle high, sample on falling edge). Attempting Mode 1,1 communication will result in misaligned data sampling and corrupted reads/writes. The device's timing diagrams and functional description explicitly define Mode 0,0 behavior, and no alternate modes are implemented in silicon.

How does the HOLD pin function during an active SPI transaction on the 25AA256X-I/ST?

When the HOLD pin is pulled low during an active SPI transaction on the 25AA256X-I/ST, the device immediately pauses communication: SI, SO, and SCK inputs are ignored (except CS), and SO enters high-impedance state. The internal state - including address pointer and instruction context - is preserved. To resume, HOLD must be returned high while SCK is low; then normal SPI operation continues from the exact bit position where it paused. This avoids retransmission overhead in interrupt-driven systems.

Can the 25AA256X-I/ST be used as a direct replacement for the 25LC256-I/ST in an existing design?

The 25AA256X-I/ST is pin-compatible and functionally identical to the 25LC256-I/ST in TSSOP-8 packaging, but supports a wider 1.8–5.5 V supply range versus 2.5–5.5 V. If the host system operates consistently above 2.5 V, substitution is safe and transparent. However, if VCC can fall below 2.5 V (e.g., during battery discharge), the 25AA256X-I/ST adds operational margin - no firmware or layout changes are needed beyond verifying voltage compliance.

What happens to the write enable latch after a successful write operation on the 25AA256X-I/ST?

After a successful WRITE, WRSR, or WRDI instruction, the write enable latch (WEL) in the 25AA256X-I/ST is automatically reset to '0'. This means every write operation - whether byte, page, or status register - must be preceded by a fresh WREN instruction. The latch also resets on power-up and is unaffected by CS toggling alone. This design prevents accidental writes due to residual latch state, enforcing explicit write-enable discipline in firmware.