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Microchip Technology 24LC21/SN
- Part No.:
- 24LC21/SN
- Manufacturer:
- Microchip Technology
- Category:
- Memory
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
24LC21/SN.pdf
- Description:
- IC EEPROM 1KBIT I2C 400KHZ 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,868
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Product details
Overview
The 24LC21/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, 100 kHz/400 kHz clock compatibility, and 1 million erase/write cycles. It serves as a DDC1/DDC2-compliant monitor identification memory in display systems.
For engineers reviewing the 24LC21/SN datasheet, 24LC21/SN pinout, 24LC21/SN application, or 24LC21/SN equivalent, key selection considerations include its unique VCLK-controlled Transmit-only mode, SCL-triggered mode transition, write-protection via VCLK logic level, page-write buffer (8 bytes), and support for extended temperature ranges (–40°C to +85°C).
Technical Context
The 24LC21/SN implements two independent serial protocols on shared SDA: a unidirectional Transmit-only mode synchronized to VCLK (for DDC monitor ID streaming), and a bidirectional I²C-compliant mode triggered by SCL edge detection. Mode persistence is stateful-power removal is required to reset from Bidirectional back to Transmit-only.
Its internal architecture includes Schmitt-triggered SCL/SDA inputs with 50 ns spike suppression, a 128-byte EEPROM array with auto-erase, an 8-byte page latch, and VCC threshold detection (<1.5 V disable). Write protection is enforced by VCLK logic level: high enables writes; low disables all writes, including in Bidirectional mode.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Memory size | 128 × 8 bits - fixed 128-byte capacity; no address extension or bank switching. |
| Supply voltage | 2.5V to 5.5V - supports legacy 3.3V and 5V systems; operates down to 2.5V at 100 kHz. |
| I²C speed modes | 100 kHz (2.5V) / 400 kHz (5V) - dual-speed compliance requires voltage-aware bus timing design. |
| Write endurance | 1,000,000 cycles - guaranteed minimum; not tested per unit but ensured by characterization. |
| Data retention | >200 years - specified at 25°C; degrades with elevated temperature and write cycling. |
| Active current | 1 mA typical at 5.5V - impacts power budget in active read/write; standby drops to 10 µA at 5.5V. |
| Page buffer size | 8 bytes - limits atomic page writes to single physical page (0–7, 8–15, ..., 120–127); crossing boundaries wraps. |
Pinout & Package
Available in 8-pin PDIP and narrow-body SOIC (SN) packages. The 24LC21/SN uses the SOIC-8 (MS-012) footprint with 1.27 mm pitch, 3.91 mm body width (E1), and 4.90 mm length (D).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VCC | Power supply input | Accepts 2.5V–5.5V; internal VCC detector disables programming below ~1.5V. |
| VSS | Ground reference | Must be connected to system ground; forms return path for all I/O and internal logic. |
| SDA | Serial data I/O | Open-drain bidirectional line; requires external pull-up (2 kΩ @ 400 kHz, 10 kΩ @ 100 kHz). |
| SCL | Bidirectional clock input | Triggers mode switch from Transmit-only to Bidirectional on high-to-low edge; must be held high to stay in Transmit-only mode. |
| VCLK | Transmit-only clock / write-enable | In Transmit-only mode: clocks data out on rising edge; in Bidirectional mode: high = enable write, low = write-protect (serial ROM behavior). |
| NC (pins 1–3) | No connection | Internally unconnected; must remain floating or tied to GND/VCC per board layout best practice (no functional impact). |
Key Features
| Feature | Design Value |
|---|---|
| Dual-mode serial interface | Enables both DDC-compliant monitor ID streaming (VCLK-driven) and standard I²C configuration access (SCL-driven) on one device without external logic. |
| VCLK-based write protection | Hardware-level write-disable: pulling VCLK low prevents all writes in Bidirectional mode, enabling safe ROM-like operation. |
| Self-timed write cycle | Eliminates need for external write timing control; internal 10 ms max cycle time allows host to poll ACK instead of fixed delays. |
| Factory QTP option | Allows pre-programming of critical ID data (e.g., EDID) during manufacturing, reducing post-solder programming steps. |
| Extended temperature support | Rated for –40°C to +85°C industrial range, qualifying for embedded display controllers in harsh environments. |
Applications
| Monitor Identification (DDC) | Embedded Configuration Storage |
|---|---|
Use Scenario: Storing EDID data in LCD/LED monitors for automatic resolution and timing negotiation with host GPU. IC Role / Device Role / Timing Role: Serial ROM providing standardized DDC1/DDC2-compliant bitstream on SDA, clocked by VCLK from graphics controller. Use Value: Enables plug-and-play display detection without host-side firmware intervention; leverages dedicated Transmit-only mode for deterministic timing. | Use Scenario: Retaining calibration coefficients, user preferences, or factory settings in industrial HMIs or medical displays. IC Role / Device Role / Timing Role: Slave I²C EEPROM accessed by main MCU during boot or runtime for nonvolatile parameter storage. Use Value: Provides byte-selectable read/write capability via standard I²C protocol, supporting dynamic updates without full memory rewrites. |
| Firmware Bootloader Parameters | Legacy System Upgrade Path |
Use Scenario: Holding bootloader configuration flags (e.g., safe mode enable, firmware version lock) in set-top boxes or digital signage players. IC Role / Device Role / Timing Role: Configuration memory mapped into bootloader's initialization sequence; accessed early in power-on reset flow. Use Value: Ensures robust recovery options even after failed firmware updates; leverages 200+ year data retention for long-life deployments. | Use Scenario: Replacing obsolete 24C01/24C02 EEPROMs in legacy PC peripherals where DDC compatibility is required. IC Role / Device Role / Timing Role: Pin-compatible drop-in replacement with identical SOIC-8 footprint and I²C addressing (1010xxxR/W), plus added VCLK functionality. Use Value: Maintains backward compatibility while enabling future DDC enhancements via unused VCLK pin. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar serial EEPROM applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| 24LCS21A | Successor part with same pinout, enhanced ESD (8 kV HBM), improved AC specs, and updated qualification; not recommended for new designs per datasheet note. | Direct functional replacement with higher reliability margin; supports identical DDC and I²C use cases. | Select 24LCS21A for new designs requiring extended lifecycle support and improved robustness. |
| AT24C01C | 128-byte I²C EEPROM (1K-bit) with standard 2-wire interface only; lacks VCLK pin and Transmit-only mode; rated for 1M cycles and 100-year retention. | Requires external logic or firmware to emulate DDC streaming; suitable only for pure I²C configuration storage. | Choose AT24C01C when DDC functionality is unnecessary and cost-sensitive volume production is prioritized. |
Compared with 24LC21/SN, the 24LCS21A offers verified improvements in ESD immunity and timing margins without changing PCB layout, while the AT24C01C sacrifices DDC capability for broader distributor availability and lower unit cost in non-monitor applications.
Availability
The 24LC21/SN is available at Aetrix Electronics and suitable for display subsystems, industrial HMIs, medical imaging interfaces, and legacy PC peripheral upgrades requiring stable component supply and long-term obsolescence management.
Supply support for 24LC21/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 memory products, with a focus on embedded control and connectivity solutions.
The 24LC21/SN belongs to Microchip's legacy serial EEPROM product line, designed specifically for display industry DDC compliance and dual-mode configurability in resource-constrained systems.
FAQ
What is the primary function of the VCLK pin on the 24LC21/SN?
The VCLK pin serves two distinct roles: in Transmit-only mode, it acts as the clock input that synchronizes serial output of the full memory array on SDA; in Bidirectional mode, it functions as a hardware write-enable signal-logic high permits writes, logic low disables all writes, effectively turning the 24LC21/SN into a serial ROM. This dual role is central to the device's DDC compliance and flexible configuration use.
How does the 24LC21/SN switch between Transmit-only and Bidirectional modes?
The 24LC21/SN powers up in Transmit-only mode. A valid high-to-low transition on the SCL pin triggers an immediate switch to Bidirectional mode. There is no software command or register setting to revert-the only way to return to Transmit-only mode is to power-cycle the device. This hardwired transition ensures deterministic behavior in display identification sequences.
Can the 24LC21/SN be used as a standard I²C EEPROM without utilizing the Transmit-only mode?
Yes-the 24LC21/SN fully supports standard I²C read/write operations in Bidirectional mode using SCL/SDA only. VCLK must be held high to enable writes; leaving it unconnected or pulled high allows full EEPROM functionality. The Transmit-only mode is optional and activated only when VCLK is driven externally-standard I²C usage requires no VCLK activity.
What is the maximum number of bytes that can be written in a single page-write operation on the 24LC21/SN?
The 24LC21/SN supports a maximum of 8 bytes per page-write operation. Its internal page buffer is fixed at 8 bytes, and physical page boundaries align to 8-byte offsets (0–7, 8–15, etc.). Attempting to write more than 8 bytes before issuing a Stop condition causes wraparound within the current page, overwriting earlier bytes-not sequential advancement to the next page.
Is the 24LC21/SN still recommended for new designs?
No-the official Microchip datasheet (DS21095K, Revision K) explicitly states "Not recommended for new designs – Please use 24LCS21A." The 24LCS21A is a direct successor with identical pinout, enhanced ESD rating (8 kV vs. 4 kV), tighter AC timing, and updated process qualification, making it the preferred choice for new projects requiring long-term supply assurance.
24LC21/SN Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Microchip Technology
- Series:
- -
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tube
- Product Status:
- Active
- Programmable:
- Not 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:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SOIC
24LC21/SN FAQ
1.How can I place an order for 24LC21/SN through Aetrix?
Please submit a Request for Quotation (RFQ) for 24LC21/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 24LC21/SN reliable?
The price and inventory of 24LC21/SN are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 24LC21/SN is usually 5 days.
3.What payment methods are accepted for 24LC21/SN?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 24LC21/SN transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for 24LC21/SN?
24LC21/SN orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your 24LC21/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 24LC21/SN?
For technical support, including 24LC21/SN datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 24LC21/SN requirements.
6.How does Aetrix verify that 24LC21/SN is sourced from the original manufacturer or authorized distributors?
All 24LC21/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 24LC21/SN meets industry standards.
7.What is the process for return or replacement of 24LC21/SN?
All 24LC21/SN units undergo pre-shipment inspection (PSI). If there is an issue with 24LC21/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 24LC21/SN part is unused and in its original packaging.
Return procedure for 24LC21/SN:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
24LC21/SN Tags
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M24C02-WMN6TP
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AT24C02C-XHM-T
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AT21CS01-STUM10-T
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24LC01BT-I/OT
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M24C02-FMC6TG
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AT24CS02-SSHM-T
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93LC46BT-I/OT
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AT24C04C-SSHM-T
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24LC01BT-I/SN
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24AA02UIDT-I/OT
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AT24C08C-STUM-T
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