Microchip Technology 25AA256XT-I/ST

Overview

25AA256XT-I/ST from Microchip Technology Inc. is a 256 Kbit (32,768 × 8) SPI Serial EEPROM with 1.8–5.5 V supply range, 64-byte page write capability, and industrial temperature support (−40°C to +85°C). It features hardware write protection via WP pin and STATUS register, HOLD functionality for interrupt-safe bus suspension, and automotive AEC-Q100 qualification. Used in firmware storage, calibration data retention, and configuration memory for microcontroller-based systems.

For engineers reviewing the 25AA256XT-I/ST datasheet, 25AA256XT-I/ST pinout, 25AA256XT-I/ST application, or 25AA256XT-I/ST equivalent, key selection criteria include its 1.8 V minimum VCC, 10 MHz max clock at 4.5–5.5 V, self-timed 5 ms write cycle, 1 μA standby current, and TSSOP-8 (ST) package compatibility with space-constrained PCB layouts.

Technical Context

The 25AA256XT-I/ST implements a standard SPI Mode 0,0/Multi-Master-compatible serial interface with separate SI (data in), SO (data out), SCK (clock), CS (chip select), HOLD (bus pause), and WP (hardware write protect) signals. Its internal architecture includes an 8-bit instruction register, page latches, HV generator for EEPROM programming, and a STATUS register with WIP, WEL, BP0/BP1, and WPEN bits.

Write operations require explicit WREN instruction followed by CS high-to-low transition to initiate internal 5 ms erase/write cycle; page writes are limited to 64-byte boundaries without wraparound. The HOLD function suspends ongoing transfers while preserving internal state, enabling host MCU to service higher-priority interrupts without reinitializing the sequence.

Key Specifications

Pinout & Package

25AA256XT-I/ST is packaged in an 8-lead Thin Shrink Small Outline Package (TSSOP-8), marked "ST" in Microchip's package coding. Dimensions conform to JEDEC MO-153, body width 4.4 mm, pitch 0.65 mm.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 25LC256-I/ST, the 25AA256XT-I/ST adds 1.8 V operation and retains identical TSSOP-8 packaging and SPI timing - making it the preferred choice for low-voltage embedded systems. Versus AT25DF256A-SSH-T, it offers pin- and command-level compatibility with legacy SPI EEPROM code but at lower density and single-line throughput.

Availability

25AA256XT-I/ST is available at Aetrix Electronics and suitable for industrial automation, automotive electronics, and medical device manufacturing requiring stable component supply, long-term lifecycle support, and RoHS-compliant sourcing.

Supply support for 25AA256XT-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, FPGA, and memory solutions, headquartered in Chandler, Arizona, with global design and manufacturing operations.

The 25AA256XT-I/ST belongs to Microchip's 25XX256 family of SPI Serial EEPROMs, designed specifically for reliable, low-power, nonvolatile data storage in resource-constrained embedded systems across industrial, automotive, and medical markets.

FAQ

What is the minimum supply voltage supported by the 25AA256XT-I/ST?

The 25AA256XT-I/ST supports a minimum supply voltage of 1.8 V, enabling direct interface with modern low-voltage microcontrollers such as ARM Cortex-M0+ and RISC-V cores without level-shifting circuitry. This specification is confirmed in the Device Selection Table and DC CHARACTERISTICS section of DS20001822H, where VCC range is explicitly listed as 1.8–5.5 V for the 25AA256 variant. Operation below 1.8 V is not guaranteed and may result in undefined behavior or failure to execute write cycles.

Does the 25AA256XT-I/ST support hardware write protection independent of software control?

Yes, the 25AA256XT-I/ST supports hardware write protection through the combination of the WP pin and the WPEN bit in the STATUS register. When WPEN = 1 and WP pin is driven low, writes to the nonvolatile STATUS register bits (BP0, BP1, WPEN) are disabled - protecting critical protection settings from accidental overwrite. This dual-layer mechanism is documented in Table 2-1 (Write-Protect Functionality Matrix) and Section 2.6 of DS20001822H. Memory array writes remain unaffected unless block protection bits are also set.

What is the purpose of the HOLD pin on the 25AA256XT-I/ST, and how must it be used?

The HOLD pin on the 25AA256XT-I/ST pauses ongoing SPI transactions without resetting internal state, allowing the host MCU to service higher-priority interrupts and resume communication seamlessly. To activate HOLD, the pin must be pulled low while SCK is low; releasing HOLD while SCK remains low resumes transmission from the exact bit position. This behavior is defined in Section 3.6 and Figure 1-1 of DS20001822H. Improper timing (e.g., asserting HOLD during SCK high) delays activation until the next SCK edge, risking data corruption.

How many write/erase cycles is the 25AA256XT-I/ST rated for, and under what conditions?

The 25AA256XT-I/ST is rated for 1,000,000 write/erase cycles, as specified in Table 1-3 (AC CHARACTERISTICS) of DS20001822H. This endurance value is characterized at 25°C and VCC = 5.5 V. Microchip's Total Endurance™ Model - available on their website - provides application-specific estimates accounting for temperature, voltage, and pattern effects. Field reliability data confirms this rating applies across the full industrial temperature range (−40°C to +85°C) when operated within datasheet limits.

Is the 25AA256XT-I/ST pin-compatible with other packages in the 25XX256 family?

Yes, the 25AA256XT-I/ST in TSSOP-8 (ST) package shares identical pinout and electrical behavior with other 8-lead variants including PDIP (P), SOIC (SN/SM), and DFN (MF), as confirmed in the Pin Function Table and Package Types diagram on DS20001822H page 1. All variants use the same pin numbering (CS=1, SO=2, WP=3, VSS=4, SI=5, SCK=6, HOLD=7, VCC=8) and support identical SPI command set, timing, and protection features - enabling direct PCB footprint substitution where package height and thermal requirements allow.