Microchip Technology 24LC21-I/SN

Overview

24LC21-I/SN from Microchip Technology Inc. is a 128 × 8-bit I²C-compatible serial EEPROM with dual-mode operation (Transmit-only and Bidirectional), 2.5V–5.5V supply range, 1 mA typical active current, 10 µA typical standby current at 5.5V, and 1,000,000 erase/write cycles - designed for monitor identification via DDC1/DDC2 interface in display systems.

For engineers reviewing the 24LC21-I/SN datasheet, 24LC21-I/SN pinout, 24LC21-I/SN application, or 24LC21-I/SN equivalent, this page delivers verified electrical specs, mode-specific timing, VCLK/SCL functional separation, SOIC-8 package mapping, and real-world use context for display configuration storage and legacy DDC compliance.

Technical Context

The 24LC21-I/SN implements two independent serial protocols: Transmit-only mode uses VCLK as clock input and SDA as unidirectional output for continuous memory streaming (e.g., EDID broadcast), while Bidirectional mode uses SCL for I²C-compliant read/write with slave address 1010xxxR/W and acknowledges per byte. Mode transition occurs only on valid high-to-low SCL edge; power cycle required to return to Transmit-only mode.

It features Schmitt-trigger inputs on SCL/SDA with 50 ns spike suppression, internal VCC threshold detector disabling write below 1.5V, and open-drain SDA requiring external pull-up (2 kΩ for 400 kHz, 10 kΩ for 100 kHz). Write protection is controlled by VCLK logic level: high enables writes, low disables all programming - enabling ROM-like operation.

Key Specifications

Pinout & Package

24LC21-I/SN is housed in an 8-pin narrow-body SOIC (SN) package per JEDEC MS-012, with 1.27 mm pitch, 3.91 mm nominal length, and 1.55 mm nominal height. Pin 1 is bottom-left corner when notch faces up.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 24LC21-I/SN, the 24LCS21A-I/SN offers direct drop-in replacement with superior ESD tolerance and extended lifecycle support, while the AT24C01C-SSHM-T sacrifices DDC-native streaming for broader voltage range and simplified interface - requiring firmware-level EDID handling.

Availability

24LC21-I/SN is available at Aetrix Electronics and suitable for display interface design, monitor manufacturing, and industrial HMI development requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for 24LC21-I/SN 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 U.S.-based semiconductor company specializing in microcontrollers, analog devices, and nonvolatile memory solutions for embedded control applications.

The 24LC21-I/SN belongs to Microchip's legacy serial EEPROM product line, engineered specifically for display industry standards (DDC1/DDC2) and industrial-grade reliability in monitor identification and configuration storage.

FAQ

What is the primary function of the VCLK pin on the 24LC21-I/SN?

The VCLK pin serves two distinct roles: in Transmit-only mode, it acts as the clock input that times serial EDID bit output on SDA; in Bidirectional mode, it functions as a hardware write-enable control - held high to permit writes, low to lock memory. This dual role enables seamless integration into both DDC1 broadcast and I²C configuration workflows without external logic.

How does the 24LC21-I/SN enter Transmit-only mode versus Bidirectional mode?

The 24LC21-I/SN powers up automatically in Transmit-only mode. It remains there as long as SCL is held high. A valid high-to-low transition on SCL forces immediate transition to Bidirectional mode. Returning to Transmit-only mode requires a full power cycle - no software or pin sequence can trigger it otherwise. This ensures deterministic startup behavior in display systems.

Can the 24LC21-I/SN be used in a standard I²C system without DDC requirements?

Yes - the 24LC21-I/SN operates as a fully compliant I²C slave device in Bidirectional mode with 7-bit address 1010xxx and R/W bit control. It supports byte writes, page writes (up to 8 bytes), current/random/sequential reads, and ACK polling. Its 100/400 kHz timing, open-drain SDA, and Schmitt-trigger inputs meet standard I²C physical layer requirements for general-purpose configuration storage.

What is the significance of the "I" in 24LC21-I/SN?

The "I" denotes Industrial temperature grade (-40°C to +85°C), confirming that the 24LC21-I/SN is characterized and tested across this full range for parametric performance including write endurance, data retention, and AC timing. This makes it suitable for deployment in automotive infotainment displays, outdoor digital signage, and factory automation HMIs where ambient temperatures exceed commercial limits.

Why does the 24LC21-I/SN require nine VCLK cycles before valid data output in Transmit-only mode?

The nine-cycle initialization synchronizes internal state machines and resets the address pointer to a known condition before EDID streaming begins. During these cycles, SDA remains high-impedance - preventing bus contention. On the tenth rising edge of VCLK, the MSB of the first EDID byte appears. This ensures bit-aligned, glitch-free EDID transmission critical for reliable graphics card detection.