Microchip Technology 24CS256T-E/Q4B

Overview

24CS256T-E/Q4B from Microchip Technology is a 256-Kbit I²C serial EEPROM organized as 32,768 × 8-bit, supporting byte/page writes (up to 64 bytes), self-timed write cycles ≤5 ms, and high-speed I²C up to 3.4 MHz. It features a factory-programmed 128-bit serial number, user-lockable 64-byte ID page, and built-in ECC for single-bit error correction - deployed in automotive infotainment control modules requiring tamper-resistant configuration storage.

For engineers reviewing the 24CS256T-E/Q4B datasheet, 24CS256T-E/Q4B pinout, 24CS256T-E/Q4B application, or 24CS256T-E/Q4B equivalent, key selection criteria include extended temperature support (–40°C to +125°C), AEC-Q100 qualification, dual write-protection modes (hardware WP pin + software-configurable zone locking), and I²C Manufacturer ID register for system-level device authentication.

Technical Context

The 24CS256T-E/Q4B implements a two-wire I²C interface with Schmitt-trigger inputs, slope-controlled outputs, and configurable High-Speed mode (3.4 MHz at VCC ≥2.5V). Its memory architecture comprises a 256-Kbit main array (0000h–7FFFh) and a 1-Kbit Security register split into read-only 128-bit serial number (0800h–080Fh) and lockable 64-byte ID page (0840h–087Fh).

Device operation is governed by three dedicated registers: Configuration register (enables enhanced software write protection per 32-Kbit zone), Security register (supports irreversible ID page locking), and Manufacturer ID register (24-bit read-only value compliant with I²C standard). Write endurance exceeds 1 million cycles; data retention exceeds 200 years at 55°C.

Key Specifications

Pinout & Package

24CS256T-E/Q4B is packaged in an 8-lead UDFN (2 mm × 3 mm, 0.5 mm pitch) with wettable flank terminations - optimized for automated optical inspection (AOI) and high-reliability reflow in automotive PCB assembly.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AT24C256C-SSHL-T and 24AA256-I/P, the 24CS256T-E/Q4B delivers differentiated value through AEC-Q100 qualification, hardware/software dual write protection, ECC-enabled data integrity, and factory-serialized identity - making it the sole option for automotive and high-assurance industrial deployments requiring long-term data trustworthiness.

Availability

24CS256T-E/Q4B is available at Aetrix Electronics and suitable for automotive ECU calibration storage, industrial PLC configuration backup, medical device usage logging, smart meter firmware parameter storage, and ATE test fixture configuration requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for 24CS256T-E/Q4B 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 global semiconductor company specializing in microcontrollers, analog devices, and memory solutions for automotive, industrial, and communications markets.

The 24CS256T-E/Q4B belongs to Microchip's CS-series serial EEPROM family, designed specifically for automotive and high-reliability applications demanding AEC-Q100 qualification, enhanced security, and extended temperature operation.

FAQ

What is the maximum I²C clock frequency supported by the 24CS256T-E/Q4B?

The 24CS256T-E/Q4B supports I²C High-Speed mode up to 3.4 MHz when VCC is ≥2.5V and operating in Industrial temperature range. At lower voltages (1.7–2.5V) or Extended temperature range, maximum clock frequency is 1 MHz. This enables faster configuration loading in real-time control systems while maintaining backward compatibility with legacy 400 kHz and 100 kHz I²C masters.

Does the 24CS256T-E/Q4B require external pull-up resistors on SDA and SCL lines?

Yes, the 24CS256T-E/Q4B requires external pull-up resistors on both SDA and SCL lines because its I²C interface uses open-drain outputs. Recommended values are 330 Ω for 3.4 MHz operation, 2 kΩ for 1 MHz/400 kHz, and 10 kΩ for 100 kHz - selected based on bus capacitance and rise-time requirements specified in the I²C standard.

How does the built-in Error Correction Code (ECC) function in the 24CS256T-E/Q4B?

The 24CS256T-E/Q4B implements on-die ECC that automatically detects and corrects single-bit errors within any 4-byte read window. The Configuration register includes a read-only Error Correction State (ECS) latch that flags when correction has occurred - enabling system firmware to log potential memory stress events without interrupting normal operation.

Can the 128-bit serial number in the 24CS256T-E/Q4B be overwritten or modified?

No, the 128-bit serial number in the 24CS256T-E/Q4B is factory-programmed and permanently read-only. It resides in the first 16 bytes (0800h–080Fh) of the Security register and is globally unique across all CS-series EEPROMs. This ensures cryptographic binding and eliminates post-production serialization effort in manufacturing.

What write protection mechanisms does the 24CS256T-E/Q4B provide?

The 24CS256T-E/Q4B offers dual write protection: (1) hardware-based via the WP pin (active-high, disables all writes when tied to VCC), and (2) software-configurable via the locked Configuration register, which enables independent protection of any of eight 32-Kbit memory zones. Both methods coexist and can be used simultaneously for defense-in-depth security.

Is the 24CS256T-E/Q4B pin-compatible with older Microchip EEPROMs like the 24LC256?

Yes, the 24CS256T-E/Q4B maintains pin-to-pin compatibility with 24AA256, 24LC256, and 24FC256 in all common packages including SOIC, TSSOP, and UDFN. Its 8-lead UDFN footprint matches the Q4B variant exactly - allowing direct replacement in existing layouts without PCB revision, provided system firmware leverages the enhanced features (ECC, Security register) appropriately.