Microchip 24LC1025T-E/SN 1024K I2C Serial EEPROM: Features and Design Considerations
The Microchip 24LC1025T-E/SN is a high-density, 1,048,576-bit (1024K) serial EEPROM memory device organized as 128K x 8 bits. It is a cornerstone component for applications requiring non-volatile data storage with low power consumption and a simple interface. Its utilization of the ubiquitous I2C (Inter-Integrated Circuit) protocol makes it an attractive choice for designers working with microcontrollers, which often feature dedicated hardware for this bus.
Key Features and Advantages
The 24LC1025T-E/SN stands out due to a suite of features engineered for robust performance and design flexibility.
High-Density Memory: With 1024K bits (128KB) of storage, this EEPROM provides ample space for storing system parameters, user data, calibration constants, and event logs, eliminating the need for multiple lower-density memory chips.
I2C Serial Interface: The device communicates via a simple, two-wire I2C bus (SDA and SCL), significantly reducing the number of I/O pins required on the host microcontroller compared to parallel EEPROMs. This simplifies board layout and minimizes component count.
Wide Voltage Operation: It operates across a broad voltage range of 2.5V to 5.5V, making it compatible with a wide array of systems, from low-power 3.3V designs to legacy 5V systems.
Page Write Capability: The memory is configurable for page writes of up to 128 bytes. This allows for more efficient data transfer, as multiple bytes can be written in a single write cycle, drastically improving throughput compared to single-byte writes.
Hardware Write-Protect Pin: A dedicated WP (Write-Protect) pin allows the host system to disable all write operations to the entire memory array. This is a critical feature for protecting firmware or vital data from corruption during power-up/down sequences or system noise.
High Reliability: The device is specified for 1,000,000 erase/write cycles per byte and offers >200 years of data retention, ensuring data integrity over the lifetime of the product.
Extended Temperature Range: The ‘-E’ suffix denotes its operation over an industrial temperature range (-40°C to +85°C), suitable for harsh environments beyond typical commercial applications.
Critical Design Considerations
While the 24LC1025T-E/SN is simple to integrate, several key factors must be considered for a successful implementation.
1. I2C Addressing and Memory Organization: A unique aspect of this 1024K device is its internal memory banking. The entire address space is accessed using a 17-bit address, which exceeds the standard 2-byte (16-bit) addressing of smaller I2C EEPROMs. This is managed by using a Block Select bit embedded within the device address byte. The device has two possible base addresses (0xA0 or 0xA8), determined by the state of its A2 pin. The Block Select bit (bit 1 of the control byte) toggles between the lower 512K block (0) and the upper 512K block (1). The designer must ensure the firmware correctly manages this bit to access the full memory space.
2. Pull-Up Resistor Selection: The I2C bus requires external pull-up resistors on both the SDA and SCL lines. Their value is a critical trade-off. Values that are too low (e.g., 1kΩ) cause excessive current draw, while values that are too high (e.g., 10kΩ) can lead to slow rise times and signal integrity issues at higher clock speeds. A value between 2.2kΩ and 4.7kΩ for a 3.3V-5V system is a common starting point, but should be validated with an oscilloscope to ensure clean signal edges.
3. Write Cycle Timing: The EEPROM requires a finite time, termed the `t_WR` write cycle time (typically 5ms max), to program data into the non-volatile memory after receiving a STOP condition. The host microcontroller must poll the device for acknowledgment after this period before initiating a new write command. Failing to honor this timing will result in data not being written correctly.
4. Noise Immunity and Board Layout: As a serial device operating with precise timing, the system must be designed for good signal integrity. Keep I2C trace lengths short, route them away from noise sources, and consider using a small series resistor (e.g., 100Ω) in line with SDA/SCL to dampen ringing and overshoot.
5. Packaging (SN): The /SN suffix indicates an 8-lead Narrow SOIC package. This is a common and easy-to-solder package, but designers must be mindful of its pin pitch (0.05 inches or 1.27mm) for PCB footprint creation.
ICGOOODFIND
The Microchip 24LC1025T-E/SN is a highly reliable and versatile serial EEPROM solution, offering a compelling combination of high density, a simple two-wire interface, and robust data retention. Its successful integration hinges on careful attention to I2C bus management, precise adherence to write cycle timing, and sound PCB layout practices. For designs requiring secure, non-volatile storage in a space and pin-efficient manner, this device remains a top-tier choice.
Keywords:
1. I2C EEPROM
2. Non-volatile Memory
3. Page Write
4. Write Protection
5. Hardware Design
