Microchip Technology 24LC256-I/ST

Overview

24LC256-I/ST from Microchip Technology is a 256-Kbit I²C serial EEPROM with 32K × 8 organization, operating from 2.5V to 5.5V, supporting up to 400 kHz clock frequency, and rated for industrial temperature range (–40°C to +85°C). It features 64-byte page write buffer, hardware write-protection via WP pin, and Schmitt-trigger inputs for noise immunity - deployed in embedded system configuration storage, sensor calibration data retention, and power-fail-safe parameter logging.

For engineers reviewing the 24LC256-I/ST datasheet, 24LC256-I/ST pinout, 24LC256-I/ST application, or 24LC256-I/ST equivalent, key selection criteria include VCC min/max compliance (2.5V–5.5V), I²C timing at 400 kHz, WP-enabled hardware lock, page write time ≤5 ms, and SOIC-8 package compatibility with legacy PCB footprints.

Technical Context

The 24LC256-I/ST implements a two-wire I²C interface with open-drain SDA/SCL requiring external pull-ups, and uses internal address pointer logic to support current-address, random, and sequential read modes across its full 0000h–7FFFh memory map. Its cascading capability allows up to eight devices on one bus using A0/A1/A2 address pins.

Write operations are self-timed and internally managed: byte writes complete in ≤5 ms, and page writes (up to 64 bytes within a single 64-byte-aligned physical page) also require ≤5 ms. During active write cycles, the device inhibits ACK responses - enabling reliable acknowledge polling for host synchronization without fixed delay loops.

Key Specifications

Pinout & Package

24LC256-I/ST is supplied in an 8-lead SOIC (Small Outline Integrated Circuit) package, 3.90 mm body width, with standard 1.27 mm pitch. Pin 1 is marked by a notch or dot; orientation follows JEDEC MS-012.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 24LC256-I/ST, the 24AA256-I/ST offers broader voltage flexibility at no cost to footprint or software, while the AT24C256 demands careful timing margin analysis and lacks Microchip's automotive qualification path.

Availability

24LC256-I/ST is available at Aetrix Electronics and suitable for industrial sensor nodes, medical device calibration storage, and smart energy meter firmware settings requiring stable component supply across multi-year production lifecycles.

Supply support for 24LC256-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 components, and memory solutions, headquartered in Chandler, Arizona, with global manufacturing and support infrastructure.

The 24LC256 belongs to Microchip's serial EEPROM product line, designed specifically for reliable, low-power, I²C-based nonvolatile data storage in space-constrained embedded systems with stringent longevity requirements.

FAQ

What is the minimum VCC voltage supported by the 24LC256-I/ST?

The 24LC256-I/ST requires a minimum VCC of 2.5V and operates up to 5.5V. Unlike the 24AA256 variant, it is not specified for operation below 2.5V - attempting sub-2.5V supply may result in undefined behavior or write failure. Always verify VCC stability within this window during brown-out conditions.

Does the 24LC256-I/ST support 1 MHz I²C communication?

No, the 24LC256-I/ST is rated for maximum clock frequency of 400 kHz across its full VCC range (2.5V–5.5V). The 1 MHz capability is exclusive to the 24FC256 variant. Using 1 MHz with 24LC256-I/ST violates AC timing specifications and will cause communication failures or data corruption.

How does hardware write-protection work on the 24LC256-I/ST?

The WP pin on the 24LC256-I/ST enables hardware-level write lock: when pulled high to VCC, all write commands (byte and page) are ignored - though the device still acknowledges the I²C address and control byte. Reads remain fully functional. This provides fail-safe protection against accidental or malicious firmware overwrites.

Can multiple 24LC256-I/ST devices share the same I²C bus?

Yes - up to eight 24LC256-I/ST devices can coexist on one I²C bus using unique combinations of A0, A1, and A2 address pins. Each device responds only to its assigned 7-bit address (1010A2A1A0), enabling scalable memory expansion without additional GPIO or bus switches.

What is the page write boundary alignment requirement for the 24LC256-I/ST?

The 24LC256-I/ST enforces strict 64-byte page boundaries: valid page write addresses must be integer multiples of 64 (e.g., 0x0000, 0x0040, 0x0080). Writing across a boundary (e.g., starting at 0x003F with 64 bytes) wraps data to the start of the same page instead of crossing into the next - requiring firmware to split such writes manually.