Part A
24LC21AT/SN
マイクロチップ・テクノロジー
- Lifecycle
- Active
- Stock
- 4371 個数
- Package
- SOIC-8
- Series
- メモリ
Replacement verdict
Not a drop-in replacement
The 24LC256T-E/SN and 24LC21AT/SN are not functionally interchangeable. Although both are Microchip I²C serial EEPROM devices in SOIC-8 packages, they differ fundamentally in memory organization, device addressing, and intended application architecture. The 24LC256T-E/SN is a 256 Kbit standard I²C EEPROM, while the 24LC21AT/SN is a 1 Kbit device designed specifically for VESA DDC monitor applications with a fixed slave address. Designers must not substitute one for the other without a full redesign of the memory map, addressing scheme, and host firmware.
Different memory density
Different device addressing
Different protocol compliance
Different application architecture
Parts at a glance
Part B
24LC256T-E/SN
マイクロチップ・テクノロジー
- Lifecycle
- Active
- Stock
- 5813 個数
- Package
- SOIC-8
- Series
- メモリ
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 24LC256T-E/SN | 24LC21AT/SN | Why it matters |
|---|---|---|---|
| Memory Size | 256 Kbit | 1 Kbit | Memory density determines how much data can be stored; a 256 Kbit device holds 256 times more data than a 1 Kbit device, making them non-substitutable for storage capacity. |
| Memory Organization | 32K x 8 | 128 x 8 | Organization defines the word width and number of addressable locations, which affects addressing scheme and firmware compatibility. |
| Interface Type | I2C (2-wire) | I2C (2-wire) | Both use the same I2C serial interface, so bus protocol compatibility is maintained between the two devices. |
| Clock Frequency (Max) | 400 kHz | 400 kHz | Maximum clock speed determines data throughput; identical ratings mean comparable read/write timing performance. |
| Supply Voltage Range | 2.5 V to 5.5 V | 2.5 V to 5.5 V | Operating voltage range must match the system power rail; identical ranges allow use in the same supply environments. |
| Operating Temperature Range | -40°C to +125°C | -40°C to +85°C | The extended temperature grade of the 24LC256T-E/SN supports harsher environments, while the 24LC21AT/SN is limited to standard industrial range. |
| Package / Mounting | 8-SOIC (Surface Mount) | 8-SOIC (Surface Mount) | Identical package and mounting type allow direct PCB footprint compatibility without layout changes. |
| Write Cycle Time (Max) | 5 ms | 10 ms | Write cycle time affects how quickly data can be committed to memory; the 24LC256T-E/SN writes faster, impacting system responsiveness. |
| Endurance (Write Cycles) | 1,000,000 | 1,000,000 | Endurance indicates how many write/erase cycles the memory can withstand; identical ratings mean similar long-term reliability. |
| Data Retention | 200 years | 200 years | Data retention specifies how long stored data remains valid without power; identical values indicate equivalent non-volatile storage longevity. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 24LC21AT/SN | 24LC256T-E/SN |
|---|---|---|
| Part Status | Active | Active |
| Memory Type | Non-Volatile | Non-Volatile |
| Memory Format | EEPROM | EEPROM |
| Technology | EEPROM | EEPROM |
| Memory Size | 1Kb (128 x 8) | 256Kb (32K x 8) |
| Memory Interface | I²C | I²C |
| Clock Frequency | 400 kHz | 400 kHz |
| Write Cycle Time - Word Page | 10ms | 5ms |
| Access Time | 900 ns | 900 ns |
| Voltage - Supply | 2.5V ~ 5.5V | 2.5V ~ 5.5V |
| Operating Temperature | 0°C ~ 70°C (TA) | -40°C ~ 125°C (TA) |
| Mounting Type | Surface Mount | Surface Mount |
Frequently asked questions
What are the primary differences between the 24LC256T-E/SN and the 24LC21AT/SN?
The 24LC256T-E/SN is a 256 Kbit (32 Kbyte) I2C serial EEPROM with a 2-wire interface, operating from 1.7 V to 5.5 V, and is specified for the extended temperature range of -40°C to +125°C. The 24LC21AT/SN is a 2 Kbit (256 byte) I2C serial EEPROM with a 2-wire interface, operating from 2.5 V to 5.5 V, and is specified for the industrial temperature range of -40°C to +85°C. The two devices differ in memory density, voltage range, and temperature grade.
Are the 24LC256T-E/SN and 24LC21AT/SN pin-to-pin compatible?
Both devices are offered in an 8-pin SOIC (SN) package and use the same standard I2C pinout: A0, A1, A2, VSS, SDA, SCL, WP, and VCC. However, pin-to-pin compatibility does not guarantee functional interchangeability because the memory density, device addressing, and write-protect behavior differ. Always verify against the respective datasheets before substituting.
Can the 24LC21AT/SN be used as a direct drop-in replacement for the 24LC256T-E/SN?
No. The 24LC21AT/SN has only 2 Kbit of memory versus 256 Kbit for the 24LC256T-E/SN, so it cannot store the same amount of data. In addition, the 24LC21AT/SN supports a narrower voltage range (2.5 V to 5.5 V) and a lower maximum operating temperature (+85°C) than the 24LC256T-E/SN. A direct drop-in replacement is not possible without redesigning the memory map and validating the electrical and thermal requirements.
What is the maximum clock frequency supported by each device?
The 24LC256T-E/SN supports I2C clock frequencies up to 400 kHz (Fast mode) across its specified voltage range. The 24LC21AT/SN also supports up to 400 kHz. Both devices are compatible with standard-mode (100 kHz) and fast-mode (400 kHz) I2C buses.
How do the operating temperature ranges of the two devices compare?
The 24LC256T-E/SN is rated for the extended temperature range of -40°C to +125°C, making it suitable for automotive and industrial applications with higher thermal demands. The 24LC21AT/SN is rated for the industrial temperature range of -40°C to +85°C. The 24LC256T-E/SN therefore offers a wider operating temperature range.
What are the supply voltage requirements for the 24LC256T-E/SN and 24LC21AT/SN?
The 24LC256T-E/SN operates from 1.7 V to 5.5 V, supporting low-voltage and standard 5 V systems. The 24LC21AT/SN operates from 2.5 V to 5.5 V. The 24LC256T-E/SN can therefore operate at lower supply voltages than the 24LC21AT/SN.
Do both devices support hardware write protection?
Yes. Both the 24LC256T-E/SN and the 24LC21AT/SN provide a WP (write-protect) pin that can be used to inhibit write operations to the memory array when asserted. The exact write-protect behavior and the portion of memory affected should be confirmed in the respective manufacturer datasheets.
Which device is more suitable for high-density data logging applications?
The 24LC256T-E/SN is more suitable for high-density data logging because it provides 256 Kbit (32 Kbyte) of storage, which is 128 times the 2 Kbit (256 byte) capacity of the 24LC21AT/SN. The 24LC256T-E/SN also supports a wider voltage range and a higher maximum operating temperature, which can be advantageous in demanding data-logging environments.