Microchip 25LC128T-E/SN 128K SPI Bus Serial EEPROM: Features and Application Design Guide

The Microchip 25LC128T-E/SN is a 128-Kbit serial Electrically Erasable Programmable Read-Only Memory (EEPROM) that utilizes the widely adopted Serial Peripheral Interface (SPI) bus for communication. This device is engineered for a broad range of applications requiring reliable, non-volatile data storage with a simple interface. Its combination of high density, low power consumption, and robust packaging makes it a preferred choice for designers in the consumer, automotive, and industrial sectors.

Key Features and Specifications

The 25LC128T-E/SN boasts an array of features that underscore its versatility and performance. Organized as 16,384 x 8, it provides ample storage for configuration data, calibration constants, and event logging. A critical feature is its low-power operation, with a standby current of just 1 µA (max) and an active current of 3 mA (max), which is essential for battery-powered and energy-sensitive applications.

The device supports the entire SPI bus modes (0,0 and 1,1), ensuring compatibility with a vast majority of microcontrollers and processors. It offers a maximum clock frequency of 10 MHz, enabling high-speed data transfers and efficient system throughput. For data integrity, it includes a built-in hardware write-protect (WP) pin and software protection via the `WRSR` (Write Status Register) command. This allows the entire memory array or specific blocks (1/4, 1/2, or all) to be locked against inadvertent writes.

Its operational voltage range is from 2.5V to 5.5V, accommodating both 3.3V and 5V systems without the need for level shifters. The 25LC128T-E/SN is specified over an extended industrial temperature range (-40°C to +85°C), guaranteeing reliable performance in harsh environments. Housed in a space-saving 8-lead SOIC (150-mil) package, it is ideal for applications with stringent PCB space constraints.

Application Design Guide

Integrating the 25LC128T-E/SN into a system is straightforward, thanks to the simplicity of the SPI protocol. The interface requires only four signals: SI (Serial Input), SO (Serial Output), SCK (Serial Clock), and CS (Chip Select).

1. Hardware Connection:

Connect the SPI pins of the EEPROM directly to the SPI master (e.g., a microcontroller). The `CS` pin must be controlled by a GPIO pin on the MCU. The `WP` pin can be tied to VCC for permanent hardware write-disable or controlled by another GPIO for dynamic protection. The `HOLD` pin, which pauses serial communication without deselecting the device, can be tied to VCC if not used.

2. Communication Protocol:

All operations are initiated by pulling the `CS` pin low. The master then sends an 8-bit instruction opcode (e.g., `READ`, `WRITE`, `WREN`, `RDSR`) followed by a 16-bit address. For read operations, data is clocked out on the `SO` pin immediately after the address is sent. For write operations, data is clocked in on the `SI` pin.

3. Critical Write Cycle Consideration:

A fundamental aspect of EEPROM operation is the write cycle time. After issuing a `WRITE` (`WRITE` or `WRSR`) command, the device enters a self-timed internal write cycle (typically 5 ms max). During this time, the Status Register (`SR`) can be polled by sending a `RDSR` command and checking the Write-In-Progress (WIP) bit. The `WIP` bit is '1' during the write cycle and '0' upon completion. It is crucial that the system firmware incorporates this polling routine to avoid attempting a new write operation before the previous one is finished, ensuring data integrity.

4. Software Protection:

Before any write sequence, the Write Enable Latch (WEL) must be set by sending a `WREN` (Write Enable) instruction. This latch is automatically reset upon completion of a write cycle or by a `WRDI` (Write Disable) command. This two-step process (Enable -> Write) provides an additional software safeguard against accidental data corruption.

ICGOOODFIND Summary

The Microchip 25LC128T-E/SN is a highly reliable and efficient SPI EEPROM solution, offering a optimal blend of capacity, speed, and power efficiency. Its robust feature set, including flexible software and hardware write protection, makes it exceptionally well-suited for demanding applications across automotive, industrial, and consumer electronics. Its ease of integration and adherence to the standard SPI protocol further solidify its position as a go-to component for non-volatile memory needs.

Keywords:

SPI EEPROM

Non-volatile Memory

Write Protection

Low-power Operation

Serial Peripheral Interface