Microchip Technology 24AA256T-E/ST

Overview

24AA256T-E/ST from Microchip Technology is a 256-Kbit I²C serial EEPROM in an 8-lead SOIC package, operating from 1.7V to 5.5V with 400 kHz max clock frequency and industrial temperature range (–40°C to +85°C). It features 64-byte page write buffer, hardware write-protection via WP pin, and >1 million erase/write cycles - deployed in embedded system configuration storage, sensor calibration data retention, and power-fail-safe parameter backup.

For engineers reviewing the 24AA256T-E/ST datasheet, 24AA256T-E/ST pinout, 24AA256T-E/ST application, or 24AA256T-E/ST equivalent, key selection criteria include low-voltage operation down to 1.7V, Schmitt-trigger noise immunity on SDA/SCL, self-timed 5 ms write cycle, and cascading support for up to eight devices on one I²C bus.

Technical Context

The 24AA256T-E/ST implements a two-wire I²C-compatible interface with open-drain SDA/SCL requiring external pull-ups, and uses internal address pointer logic for sequential reads across its 32K × 8-bit memory array. Its write protection is controlled solely by the WP pin state at Stop bit sampling, with no software lock mechanism.

It supports byte and page write modes, where page writes are limited to 64-byte boundaries (0x0000–0x003F, 0x0040–0x007F, etc.), and enforces contiguous addressing only within device boundaries - multi-device cascading expands total address space but does not enable cross-device sequential reads.

Key Specifications

Pinout & Package

24AA256T-E/ST is housed in an 8-lead SOIC (Small Outline Integrated Circuit) package with standard 150-mil width and gull-wing leads. Pin 1 is marked with a beveled corner or dot; pin numbering follows JEDEC MS-012AA convention.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 24LC256T-I/ST, the 24AA256T-E/ST enables 1.7V operation for battery-powered designs; compared with AT24C256-10PU-2.7, it offers guaranteed industrial temperature range and tighter WP timing specs for safety-critical write-locking.

Availability

24AA256T-E/ST is available at Aetrix Electronics and suitable for smart energy meters, automotive body control modules, and industrial PLC I/O expansion requiring stable component supply, long-lifecycle assurance, and RoHS-compliant sourcing.

Supply support for 24AA256T-E/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 microcontroller, analog, and Flash-IP solutions, serving automotive, industrial, consumer, and communications markets with vertically integrated silicon and development tools.

The 24AA256T-E/ST belongs to Microchip's 24XX256 family of I²C EEPROMs, designed specifically for low-power, high-reliability nonvolatile data storage in resource-constrained embedded systems.

FAQ

What is the maximum I²C clock frequency supported by the 24AA256T-E/ST?

The 24AA256T-E/ST supports up to 400 kHz I²C clock frequency when VCC is 2.5V or higher. At VCC < 2.5V, the maximum clock rate drops to 100 kHz. This dual-speed capability ensures compatibility with both legacy 100 kHz controllers and modern 400 kHz implementations while maintaining robust signal integrity at low voltages. The 24AA256T-E/ST does not support 1 MHz operation - that capability is reserved for the 24FC256 variant.

How does the WP pin function on the 24AA256T-E/ST?

The WP (Write-Protect) pin on the 24AA256T-E/ST is a hardware-level enable/disable control sampled only at the Stop condition of each write command. When tied to VCC, all write operations (byte and page) are inhibited while read operations remain fully functional. Toggling WP during an active write cycle has no effect - protection state is latched at Stop. This provides deterministic, glitch-immune write locking without firmware involvement.

Can multiple 24AA256T-E/ST devices share the same I²C bus?

Yes, up to eight 24AA256T-E/ST devices can be cascaded on a single I²C bus using the A0, A1, and A2 address pins to configure unique 3-bit hardware addresses (1010xxx0). Each device responds only to its assigned address, enabling scalable memory expansion - for example, eight devices provide 2 Mbit total address space. The 24AA256T-E/ST's SOIC package includes all three address pins, unlike the SOT-23 variant which omits them.

What is the page write size and timing for the 24AA256T-E/ST?

The 24AA256T-E/ST features a 64-byte page write buffer, meaning up to 64 bytes can be loaded into the internal latch before initiating the actual write cycle. Once the host issues a Stop condition, the self-timed internal write completes in ≤5 ms - no external delay or polling is required, though ACK polling is supported for optimal bus utilization. Page writes must stay within physical 64-byte boundaries (e.g., 0x0000–0x003F); crossing boundaries causes wraparound, not automatic page advancement.

Is the 24AA256T-E/ST qualified for automotive applications?

The 24AA256T-E/ST is specified for Industrial temperature range (–40°C to +85°C) and is not AEC-Q100 qualified. While it shares the same die as AEC-Q100-qualified variants like the 24AA256T-I/ST (for certain packages), the 24AA256T-E/ST part number itself carries no automotive qualification. For automotive body electronics or infotainment systems requiring formal qualification, Microchip's AEC-Q100-certified 24AA256 variants (e.g., 24AA256T-I/MNY) should be selected instead.