Microchip Technology 24LCS21A-I/SNG

Overview

24LCS21A-I/SNG from Microchip Technology Inc. is a 128 × 8-bit dual-mode I²C™-compatible serial EEPROM designed for monitor identification (DDC1™/DDC2™) and configuration storage in display systems. It operates from 2.5V to 5.5V, supports both Transmit-Only (VCLK-clocked) and Bidirectional (SCL-clocked) modes, features hardware write-protection via WP pin, and delivers 1 mA active current and 10 μA standby current at 5.5V.

For engineers reviewing the 24LCS21A-I/SNG datasheet, 24LCS21A-I/SNG pinout, 24LCS21A-I/SNG application, or 24LCS21A-I/SNG equivalent, key selection considerations include DDC compliance, dual-clock domain operation (VCLK for DDC1, SCL for I²C), flexible write-protection logic (WP + VCLK interaction), page-write buffer (8-byte), and industrial temperature range (–40°C to +85°C).

Technical Context

The 24LCS21A-I/SNG implements two independent communication protocols on shared SDA: Transmit-Only mode uses VCLK as clock source for continuous EDID™ bitstream output (MSB-first, 9th null bit), while Bidirectional mode uses SCL for standard I²C™ byte-addressable read/write with slave address 1010000x. Mode transition occurs only on valid high-to-low SCL edge followed by detection of control byte '1010000X'; reverting to Transmit-Only requires power cycle.

Write protection is implemented via dual-layer logic: factory-default fuse cleared until first write to address 7Fh enables WP pin control, and VCLK must be held high during programming in Bidirectional mode. Internal self-timed write cycle (10 ms max) includes auto-erase, and noise immunity is ensured by Schmitt-trigger inputs (SDA, SCL, VCLK) with 50 ns spike suppression and 5% hysteresis.

Key Specifications

Pinout & Package

24LCS21A-I/SNG is housed in an 8-pin SOIC package (SOIC-8, 150 mil body, RoHS-compliant, industrial temperature grade).

Key Features

Applications

Equivalent & Alternatives

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

Compared with AT24C02C-SSHM-T and ST M24C02-RMN6TP, the 24LCS21A-I/SNG uniquely integrates VESA®-compliant DDC1™/DDC2™ protocol handling into silicon - eliminating host CPU involvement in EDID™ transmission and enabling true plug-and-play monitor identification with minimal external circuitry.

Availability

24LCS21A-I/SNG is available at Aetrix Electronics and suitable for display interface design, monitor manufacturing, and embedded video system integration requiring stable component supply and industrial-grade reliability.

Supply support for 24LCS21A-I/SNG 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 24LCS21A-I/SNG belongs to Microchip's DDC-compliant serial EEPROM product line, engineered specifically for display interface applications requiring seamless EDID™ management and dual-protocol flexibility in space-constrained designs.

FAQ

What is the primary function of the VCLK pin on the 24LCS21A-I/SNG?

The VCLK pin serves two distinct roles: in Transmit-Only mode, it acts as the clock input for continuous EDID™ bitstream output (rising-edge triggered); in Bidirectional mode, it functions as a write-enable control - writes are blocked unless VCLK is held high. This dual functionality enables seamless DDC1™ compatibility while retaining I²C™ programmability. The 24LCS21A-I/SNG leverages VCLK to eliminate host polling in monitor identification scenarios.

How does the 24LCS21A-I/SNG enter Bidirectional mode from power-on state?

The 24LCS21A-I/SNG powers up in Transmit-Only mode and remains there until a valid high-to-low transition is detected on the SCL pin. Upon this edge, it enters Transition mode and listens for its I²C™ slave address (1010000x) on the bus. If received within 128 VCLK pulses, it switches permanently to Bidirectional mode; otherwise, it reverts to Transmit-Only mode. Power removal is required to reset to Transmit-Only mode. This behavior is intrinsic to the 24LCS21A-I/SNG architecture.

Can the 24LCS21A-I/SNG be used as a standard I²C™ EEPROM without DDC functionality?

Yes - the 24LCS21A-I/SNG fully supports standard I²C™ byte and page write/read operations using slave address 1010000x, with ACK polling and 400 kHz fast-mode timing. Its DDC-specific features (VCLK, Transmit-Only mode) are inactive unless explicitly engaged; the core EEPROM functionality operates identically to conventional I²C™ devices. Engineers may deploy the 24LCS21A-I/SNG in non-DDC systems while retaining full compatibility with existing I²C™ drivers.

What happens if a page write crosses a physical page boundary on the 24LCS21A-I/SNG?

If a page write command attempts to write across a physical page boundary (i.e., beyond address 7Fh when starting at 78h), the 24LCS21A-I/SNG wraps the data back to the start of the current 8-byte page instead of advancing to the next page. This overwrite behavior is documented in the datasheet and applies exclusively to the 24LCS21A-I/SNG's 8-byte page buffer architecture - software must enforce page-aligned writes to prevent unintended data loss.

How is write protection implemented on the 24LCS21A-I/SNG?

Write protection on the 24LCS21A-I/SNG uses a two-stage mechanism: first, writing any value to address 7Fh sets an internal fuse that activates the WP pin; second, once enabled, WP (active-low) and VCLK (high-required) jointly control write access per Table 6-1. Until the fuse is set, the device is always writable if VCLK = 1. This design allows factory programming before fuse activation and field-safe reconfiguration. The 24LCS21A-I/SNG thus provides configurable, layered security against accidental writes.