Microchip 25LC128T-E/ST 128K SPI Bus Serial EEPROM: Datasheet, Pinout, and Application Circuit Design

The Microchip 25LC128T-E/ST is a 128-Kbit (16 Kbyte) Serial Electrically Erasable Programmable Read-Only Memory (EEPROM) that employs the widely adopted Serial Peripheral Interface (SPI) bus for communication. This device is engineered for reliable non-volatile data storage in a vast array of applications, from consumer electronics to industrial systems. Its high-speed clock support, low power consumption, and robust endurance make it a premier choice for designers.

Datasheet Overview and Key Features

The datasheet for the 25LC128T-E/ST reveals a component designed for performance and resilience. Key specifications include:

Memory Organization: 256 pages of 64 bytes each, totaling 131,072 bits.

SPI Interface: Supports clock frequencies up to 10 MHz, enabling high-speed data transfers.

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

Endurance and Retention: Rated for >1,000,000 erase/write cycles per sector and data retention of >200 years.

Low Power Operation: The entire family is designed for low-power operation, making it ideal for battery-powered devices. The `-E` suffix indicates an extended temperature range (-40°C to +125°C), suiting it for automotive and industrial environments.

Instruction Set: A simple and efficient set of commands for Read, Write, Write Enable, and Read Status Register operations.

Pinout Configuration

The 25LC128T-E/ST is available in an 8-lead TSSOP package. Its pinout is crucial for correct circuit integration:

1. Chip Select (/CS): Input to select the device when active low.

2. Serial Clock (SCK): Input for the SPI clock signal, provided by the master controller.

3. Serial Data Input (SI): Input line for data and commands shifted into the device.

4. Serial Data Output (SO): Output line for data shifted out during read operations.

5. Write Protect (/WP): When driven low, this hardware pin disables write operations to the status register, providing a hardware-level safety feature.

6. Hold (/HOLD): Allows the serial communication to be paused without terminating the operation, useful when the SPI bus is shared.

7. VCC: Power Supply (+1.8V to +5.5V).

8. VSS: Ground.

Application Circuit Design

Integrating the 25LC128T-E/ST into a system is straightforward. A typical application circuit for an SPI connection with a microcontroller (MCU) is shown below.


Basic Interfacing Circuit between a Microcontroller and the 25LC128T-E/ST

Design Considerations:

1. Power Supply (VCC): Decouple the VCC pin with a 0.1µF ceramic capacitor placed as close to the device as possible to filter noise.

2. SPI Lines: Connect the SCK, SI (MOSI), and SO (MISO) lines directly to the corresponding SPI pins on the host MCU. The /CS line must be controlled by a digital output GPIO pin on the MCU.

3. Write Protect (/WP): For permanent hardware write protection, this pin can be tied to GND. For MCU-controlled protection, connect it to a GPIO pin. If not used, it is recommended to tie it to VCC to disable the protection feature.

4. Hold (/HOLD): If the hold function is not required, this pin should be tied directly to VCC to ensure uninterrupted operation.

5. Pull-up Resistors: While the MCU’s internal pull-ups are often sufficient, external 4.7kΩ - 10kΩ pull-up resistors on the /CS, /WP, and /HOLD lines can enhance signal integrity in electrically noisy environments.

Firmware Operation

The basic firmware flow involves:

Initiating a Write: Pull /CS low, send the WREN (Write Enable) instruction (0x06), then pull /CS high. Pull /CS low again to send the WRITE instruction (0x02), followed by the 16-bit address and the data bytes.

Initiating a Read: Pull /CS low, send the READ instruction (0x03), followed by the 16-bit address. The data stored at that address will then be clocked out on the SO line.

Always check the BUSY bit in the Status Register before initiating a new write sequence to ensure the previous operation is complete.

ICGOOODFIND

The Microchip 25LC128T-E/ST stands out as a highly reliable and versatile SPI EEPROM solution. Its combination of a simple interface, robust hardware write protection, extended temperature capability, and high endurance makes it an excellent choice for designers needing dependable non-volatile memory in demanding applications. Its ease of integration with any modern MCU further solidifies its position as a go-to component for data storage tasks.

Keywords:

1. SPI EEPROM

2. Non-volatile Memory

3. Hardware Write Protection

4. Serial Peripheral Interface

5. Application Circuit