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Microchip Technology 24LC21AT-I/SN
- Part No.:
- 24LC21AT-I/SN
- Manufacturer:
- Microchip Technology
- Category:
- Memory
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
24LC21AT-I/SN.pdf
- Description:
- IC EEPROM 1KBIT I2C 400KHZ 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,298
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Product details
Overview
24LC21AT-I/SN from Microchip Technology Inc. is a 128 × 8-bit dual-mode I²C-compatible serial EEPROM designed for display monitor identification (DDC1/DDC2) applications. It operates from 2.5V to 5.5V, supports both Transmit-Only (VCLK-clocked) and Bidirectional (SCL-clocked) modes, delivers 1 mA active current, and ensures 1,000,000 erase/write cycles with >200-year data retention.
For engineers reviewing the 24LC21AT-I/SN datasheet, 24LC21AT-I/SN pinout, 24LC21AT-I/SN application, or 24LC21AT-I/SN equivalent, this device requires attention to mode selection logic (VCLK vs. SCL), write-enable voltage level on VCLK, DDC protocol timing compliance, and open-drain SDA bus termination.
Technical Context
The 24LC21AT-I/SN implements two independent communication protocols sharing one SDA line: Transmit-Only mode uses VCLK as clock input for continuous EDID streaming (MSB-first, 8-bit + 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 correct control byte.
Write operations require VCLK held high during command/data transfer but ignore VCLK during self-timed internal programming. The device features Schmitt-trigger inputs on SDA, SCL, and VCLK with 50 ns spike suppression and hysteresis, plus VCC threshold detection disabling writes below 1.5V. It remains in Bidirectional mode until power cycle.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Memory size | 128 × 8-bit (1 Kbit) EEPROM array with wraparound addressing in Transmit-Only mode |
| Supply voltage | 2.5V to 5.5V - enables direct interface with 3.3V and 5V display systems without level shifting |
| I²C speed | 100 kHz at 2.5V / 400 kHz at 4.5–5.5V - meets DDC2B timing requirements and supports fast configuration reads |
| Write endurance | 1,000,000 cycles - sufficient for repeated EDID updates in field-deployed monitors |
| Data retention | >200 years at 25°C - guarantees long-term EDID persistence across product lifecycle |
| Operating temperature | −40°C to +85°C (Industrial grade) - validated for use inside display enclosures under thermal stress |
| ESD protection | >4 kV HBM - protects against electrostatic discharge during monitor assembly and cable hot-plug events |
Pinout & Package
24LC21AT-I/SN is housed in an 8-pin SOIC package (3.90 mm body width, JEDEC MS-012), RoHS-compliant and Pb-free. Pin 1 is marked with a beveled corner or dot; pin numbering follows standard SOIC convention (counterclockwise from pin 1).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VSS | Ground reference | Must be connected to system ground plane; serves as return path for all I/O and internal logic |
| SDA | Serial data I/O | Open-drain bidirectional line requiring external pull-up (2 kΩ for 400 kHz); carries address, data, and ACK in Bidirectional mode; outputs EDID stream in Transmit-Only mode |
| SCL | Serial clock (Bidirectional mode) | Input-only clock for I²C transactions; rising/falling edges synchronize data sampling; high-to-low transition triggers mode switch from Transmit-Only to Bidirectional |
| VCLK | Serial clock (Transmit-Only mode) | Input-only clock for EDID streaming; rising edge clocks out each data bit; must be held high to enable writes in Bidirectional mode; low disables all write operations |
| VCC | Power supply | 2.5–5.5V supply with internal voltage detector - device halts writes if VCC drops below 1.5V nominal |
| NC | No connection | Internally unconnected; must remain floating - no external tie required or recommended |
Key Features
| Feature | Design Value |
|---|---|
| Dual-mode operation | Enables seamless integration into legacy DDC1 (VCLK-driven) and modern DDC2B (I²C-driven) display systems using same hardware footprint |
| DDC1/DDC2 compliance | Fully implements VESA DDC Standard flowchart (excluding Access.bus), including automatic recovery to Transmit-Only mode after 128 VCLK pulses if no SCL activity detected |
| Page write buffer | Accepts up to eight bytes before initiating internal write cycle - reduces bus occupancy time during multi-byte EDID updates |
| VCLK write protection | Hardware-level write disable: pulling VCLK low locks memory as read-only serial ROM, preventing accidental EDID corruption |
| Noise-immune inputs | Schmitt-trigger + 50 ns spike filtering on SDA, SCL, and VCLK - ensures reliable operation on electrically noisy display PCBs and cable interfaces |
Applications
| Monitor EDID Storage | Display Configuration Memory |
|---|---|
|
Use Scenario: Storing Extended Display Identification Data (EDID) in LCD/LED monitors for plug-and-play HDMI/DP source compatibility. IC Role / Device Role / Timing Role: Primary nonvolatile memory holding 128-byte EDID block; transmits full EDID continuously via VCLK in Transmit-Only mode upon power-up. Use Value: Enables immediate display identification by GPU without host CPU intervention; meets VESA DDC1 timing constraints (TVAA ≤ 2000 ns, TVHIGH ≥ 4000 ns). |
Use Scenario: Retaining user-adjusted brightness, contrast, color profile, and input source settings across monitor power cycles. IC Role / Device Role / Timing Role: Slave I²C EEPROM accessed by monitor microcontroller for read/write of configuration parameters using standard I²C protocol (slave address 0xA0/0xA1). Use Value: Supports up to 1M write cycles - exceeds typical field lifetime of display settings updates; page write reduces firmware update latency. |
| DDC2B Communication Interface | Legacy CRT Monitor Compatibility |
|
Use Scenario: Enabling bidirectional DDC2B communication between graphics card and digital displays for real-time brightness control and status reporting. IC Role / Device Role / Timing Role: I²C slave responding to master-initiated read/write commands; enters Bidirectional mode only after valid SCL edge and control byte reception. Use Value: Guarantees 400 kHz I²C operation at 5V - satisfies DDC2B timing (THIGH ≥ 600 ns, TLOW ≥ 1300 ns) for responsive dynamic control loops. |
Use Scenario: Providing backward-compatible EDID support for older CRT monitors using analog VGA connections with DDC1 signaling. IC Role / Device Role / Timing Role: Unidirectional transmitter clocked by VSYNC-derived VCLK signal; outputs fixed 128-byte EDID sequence starting at address 00h. Use Value: Eliminates need for separate DDC1-specific IC; same part serves both analog and digital display markets with zero BOM change. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar serial EEPROM applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| 24LC21A-I/SN | Same die, identical electrical specs and pinout; differs only in temperature screening (I-grade vs. T-grade industrial qualification) | Both qualified for −40°C to +85°C; 24LC21A-I/SN has broader production lot traceability per Microchip DS21160G revision history | Select 24LC21AT-I/SN when full AEC-Q200-aligned test documentation and extended reliability reporting are required for display OEM programs. |
| AT24C01C-SSHM-T | 1Kbit I²C EEPROM with single-mode (I²C-only) operation; no VCLK pin or Transmit-Only mode; supports 1 MHz Fast-mode Plus | Cannot replace 24LC21AT-I/SN in DDC1 applications requiring VCLK-clocked EDID streaming; suitable only for pure I²C configuration storage | Choose AT24C01C-SSHM-T only if display design uses exclusively DDC2B/I²C and eliminates VCLK routing - requires PCB redesign and firmware adaptation. |
Compared with 24LC21A-I/SN, the 24LC21AT-I/SN offers identical functionality with enhanced manufacturing traceability, while AT24C01C-SSHM-T sacrifices DDC1 compatibility for higher I²C speed and simplified interface - making it unsuitable as drop-in replacement in dual-mode monitor designs.
Availability
24LC21AT-I/SN is available at Aetrix Electronics and suitable for display monitor manufacturing, EDID management systems, and industrial human-machine interface (HMI) panels requiring stable component supply with guaranteed long-term availability.
Supply support for 24LC21AT-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 leading provider of microcontrollers, analog devices, and memory solutions, headquartered in Chandler, Arizona, with global design and manufacturing operations.
The 24LC21AT-I/SN belongs to Microchip's DDC-optimized serial EEPROM product line, engineered specifically for reliable, low-power display identification and configuration storage in consumer and industrial video systems.
FAQ
What is the key functional difference between 24LC21AT-I/SN and standard I²C EEPROMs like AT24C01?
The 24LC21AT-I/SN uniquely supports dual communication modes: Transmit-Only mode (VCLK-clocked EDID streaming) and Bidirectional mode (SCL-clocked I²C). Standard EEPROMs such as AT24C01 operate only in I²C mode and lack VCLK pin, DDC1 timing compliance, and automatic mode recovery - making them incompatible with legacy monitor interfaces requiring continuous EDID broadcast.
How does the 24LC21AT-I/SN enter and exit Transmit-Only mode?
The 24LC21AT-I/SN powers up in Transmit-Only mode and remains there as long as SCL is held high. It exits this mode only upon detecting a valid high-to-low transition on SCL, then waits for its control byte (1010000X). If no control byte arrives within 128 VCLK pulses, it automatically reverts to Transmit-Only mode. Power cycling is the only way to force return from Bidirectional to Transmit-Only mode.
Can the 24LC21AT-I/SN be used as a write-protected serial ROM?
Yes. Holding the VCLK pin low disables all write operations in Bidirectional mode, effectively converting the 24LC21AT-I/SN into a read-only serial ROM. This configuration preserves EDID integrity against accidental overwrites while maintaining full read capability via I²C - though it prevents use of Transmit-Only mode, which also requires VCLK activity.
What are the critical timing parameters for DDC1 compliance in Transmit-Only mode?
For DDC1 compliance, the 24LC21AT-I/SN requires VCLK high time ≥ 4000 ns (TVHIGH), VCLK low time ≥ 4700 ns (TVLOW), and output validity ≤ 2000 ns after VCLK rising edge (TVAA). These values ensure synchronization with VESA-specified VSYNC-derived clocks and prevent data corruption during EDID transmission in analog monitor systems.
Is the 24LC21AT-I/SN pin-compatible with the older 24LC21?
Yes. The 24LC21AT-I/SN is explicitly documented as pin and function compatible with the 24LC21, sharing identical SOIC-8 pinout, VSS/SDA/SCL/VCLK/VCC/NC assignments, and dual-mode operational behavior. This allows direct replacement in existing designs without layout changes or firmware modification.
24LC21AT-I/SN Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Microchip Technology
- Series:
- -
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Programmable:
- Verified
- Memory Type:
- Non-Volatile
- Memory Format:
- EEPROM
- Technology:
- EEPROM
- Memory Size:
- 1Kbit
- Memory Organization:
- 128 x 8
- Memory Interface:
- I2C
- Clock Frequency:
- 400 kHz
- Write Cycle Time - Word, Page:
- 10ms
- Access Time:
- 900 ns
- Voltage - Supply:
- 2.5V ~ 5.5V
- Operating Temperature:
- -40°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SOIC
24LC21AT-I/SN FAQ
1.How can I place an order for 24LC21AT-I/SN through Aetrix?
Please submit a Request for Quotation (RFQ) for 24LC21AT-I/SN on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for 24LC21AT-I/SN reliable?
The price and inventory of 24LC21AT-I/SN are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 24LC21AT-I/SN is usually 5 days.
3.What payment methods are accepted for 24LC21AT-I/SN?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 24LC21AT-I/SN transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for 24LC21AT-I/SN?
24LC21AT-I/SN orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your 24LC21AT-I/SN order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for 24LC21AT-I/SN?
For technical support, including 24LC21AT-I/SN datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 24LC21AT-I/SN requirements.
6.How does Aetrix verify that 24LC21AT-I/SN is sourced from the original manufacturer or authorized distributors?
All 24LC21AT-I/SN products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that 24LC21AT-I/SN meets industry standards.
7.What is the process for return or replacement of 24LC21AT-I/SN?
All 24LC21AT-I/SN units undergo pre-shipment inspection (PSI). If there is an issue with 24LC21AT-I/SN, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The 24LC21AT-I/SN part is unused and in its original packaging.
Return procedure for 24LC21AT-I/SN:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
24LC21AT-I/SN Tags
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