Microchip 25LC128-I/SN 128K SPI Bus Serial EEPROM: Datasheet, Pinout, and Application Circuit Guide

The Microchip 25LC128-I/SN is a 128-Kbit (16-Kbyte) Serial Electrically Erasable Programmable Read-Only Memory (EEPROM) that utilizes the ubiquitous Serial Peripheral Interface (SPI) bus for communication. This device is renowned for its high reliability, low power consumption, and simple interface, making it a cornerstone for non-volatile data storage in countless embedded systems, from consumer electronics to industrial automation.

This guide provides a detailed overview of its key specifications, pinout configuration, and a practical application circuit to facilitate easy integration into your designs.

Datasheet Highlights and Key Features

The datasheet for the 25LC128-I/SN reveals a robust and feature-rich memory IC. Key parameters include:

Memory Organization: 128K bits, organized as 256 pages of 64 bytes each or a single block of 16,384 bytes.

SPI Interface: Supports all four modes of SPI (0,0 & 1,1) and clock speeds up to 10 MHz, enabling high-speed data transfers.

Voltage Range: Operates from 2.5V to 5.5V, compatible with both 3.3V and 5V microcontroller systems.

Write Protection: Features a hardware write-protect (WP) pin and software protection commands to safeguard memory contents against accidental writes.

Sequential Read: Allows for continuous read operations, streamlining data stream reading.

Low Power Consumption: boasts a low standby current (1 µA typical) and active read current (3 mA at 5.5V, 10 MHz), ideal for battery-powered applications.

Endurance: Guaranteed 1,000,000 erase/write cycles per sector and data retention of over 200 years.

Package: The "-SN" suffix denotes an 8-lead SOIC (150 mil) package, which is easy to prototype with and suitable for automated assembly.

Pinout Configuration

Understanding the pinout is crucial for correct circuit design. The 25LC128-I/SN comes in an 8-pin SOIC package.

1. Chip Select (/CS): Input. Initiates and terminates a communication session. Must be pulled low to select the device.

2. Serial Data Out (SO): Output. Used for data output from the EEPROM to the microcontroller's Master In Slave Out (MISO) line.

3. Write Protect (/WP): Input. When pulled low, this pin disables writing to the status register, providing hardware-level protection. It must be held high for normal write operations.

4. Ground (VSS): Power Supply Ground.

5. Serial Data In (SI): Input. Used for data input from the microcontroller's Master Out Slave In (MOSI) line into the EEPROM.

6. Serial Clock (SCK): Input. The clock signal provided by the SPI master (microcontroller) to synchronize data movement.

7. Hold (/HOLD): Input. Allows the master to pause serial communication without resetting the transaction, useful in shared-bus systems. Must be held high for normal operation.

8. Power Supply (VCC): Input. Connected to the positive power supply (2.5V to 5.5V).

Application Circuit Guide

A typical application circuit for interfacing the 25LC128-I/SN with an MCU is straightforward. Below is a standard connection diagram and explanation.

Components Required:

Microcontroller (MCU) with SPI peripheral (e.g., Arduino, PIC, AVR, STM32)

Microchip 25LC128-I/SN EEPROM

Pull-up resistors (10kΩ recommended for /WP, /HOLD, and /CS if not internally handled by the MCU)

Decoupling capacitor (0.1 µF ceramic)

Connection Steps:

1. Power: Connect VCC (Pin 8) to the system's positive rail (3.3V or 5V). Connect VSS (Pin 4) to system ground.

2. SPI Bus: Connect the MCU's SPI pins directly to the EEPROM:

MCU MOSI -> SI (Pin 5)

MCU MISO -> SO (Pin 2)

MCU SCK -> SCK (Pin 6)

3. Chip Select: Connect the MCU's any digital I/O pin to /CS (Pin 1). Note: While it can share the SPI bus with other devices, each requires its own unique /CS line.

4. Control Pins: For most applications, it is recommended to tie the /HOLD (Pin 7) and /WP (Pin 3) pins directly to VCC via pull-up resistors to disable their functions and ensure normal operation.

5. Decoupling: Place a 0.1 µF ceramic capacitor between VCC (Pin 8) and GND (Pin 4), as close to the EEPROM as possible, to filter high-frequency noise on the power supply.

Firmware Note: The MCU's firmware must implement the SPI protocol, toggling the /CS pin and sending the appropriate commands (e.g., WREN, WRITE, READ) as detailed in the datasheet to perform read and write operations.

ICGOODFIND: The Microchip 25LC128-I/SN stands out as an exceptionally versatile and reliable SPI EEPROM solution. Its wide voltage support, high-speed clock rate, and robust data integrity features make it an excellent choice for designers seeking a proven non-volatile memory component for a vast array of applications. Its simple 4-wire SPI interface ensures quick and easy integration, reducing development time and complexity.

Keywords: SPI EEPROM, Non-volatile Memory, Microchip 25LC128, Serial Peripheral Interface, Hardware Write Protection