Microchip 93LC66BT-I/ST 4K SPI Microwire Serial EEPROM Datasheet and Application Circuit Design Guide

The Microchip 93LC66BT-I/ST is a 4K-bit (512 x 8 or 256 x 16) Serial Electrically Erasable PROM (EEPROM) featuring the industry-standard Microwire serial interface. This device is designed for applications requiring non-volatile memory storage with low power consumption, high reliability, and a simple connection scheme to a microcontroller (MCU). Its small form factor (TSSOP-8 package) makes it ideal for space-constrained designs across consumer, industrial, and automotive electronics.

Key Features and Electrical Characteristics

The 93LC66BT-I/ST operates from a wide voltage range of 2.5V to 5.5V, supporting both 5V and lower voltage systems. It boasts a low standby current of just 1 µA (max) and an active current of 3 mA (max), which is critical for battery-powered and energy-sensitive applications. The memory array offers a minimum endurance of 1,000,000 erase/write cycles and data retention exceeding 200 years, ensuring long-term data integrity. The device supports both a 16-bit and an 8-bit organizational structure, selected via the ORG pin, providing flexibility for different system data widths.

Microwire Serial Interface Protocol

The Microwire interface is a simple, synchronous, three-wire serial bus consisting of Chip Select (CS), Serial Clock (SK), and Data Input (DI) and Output (DO) lines. Communication is initiated by the host MCU pulling the CS pin high. Instructions, addresses, and data are then clocked in and out synchronously on the rising edge of the SK signal. The protocol includes instructions for READ (READ), WRITE (WRITE), ERASE (ERASE), WRITE ALL (WRAL), ERASE ALL (ERAL), and Write Enable (EWEN)/Disable (EWDS). This straightforward command set simplifies software driver development.

Typical Application Circuit Design

A standard application circuit for interfacing the 93LC66BT-I/ST with a microcontroller is simple and requires minimal external components.

1. Power Supply (VCC): Decouple the VCC pin to ground with a 100nF ceramic capacitor placed as close to the device as possible to suppress noise.

2. Serial Interface Connections: Directly connect the four interface pins to the MCU's GPIOs:

CS: Connect to an MCU output pin.

SK: Connect to an MCU output pin (SPI SCK if emulating in software).

DI: Connect to an MCU output pin (SPI MOSI if emulating).

DO: Connect to an MCU input pin (SPI MISO if emulating).

3. ORG Pin: Connect to VCC or GND to permanently set the organization mode (8-bit or 16-bit). For flexibility, it can be driven by an additional MCU GPIO pin.

4. Ground Connection: Ensure a solid, low-impedance ground connection.

Critical Design Considerations

Pull-up Resistors: While the MCU's internal pull-ups may suffice, external 4.7kΩ to 10kΩ pull-up resistors on the CS, SK, and DI lines can enhance signal integrity, especially in electrically noisy environments.

Signal Integrity: Keep all signal traces as short as possible. For long PCB traces or high-noise environments, series termination resistors (e.g., 100Ω) on the clock and data lines may be necessary.

Write Protection: The software-controlled EWEN and EWDS instructions provide protection against accidental writes. For additional hardware protection, the CS pin can be controlled carefully in firmware to prevent erroneous activation.

Write Cycle Timing: After issuing a WRITE instruction, the device enters a self-timed internal write cycle (typically 3-4 ms). During this time, the device will not respond to commands. The MCU must poll the DO pin (which becomes ready/busy status) or simply wait for the maximum write cycle time specified in the datasheet before sending a new command.

Conclusion and Summary

The 93LC66BT-I/ST provides a robust and simple solution for adding small amounts of reliable non-volatile memory to an embedded system. Its proven Microwire interface and minimal component count make it an excellent choice for designers. By following the datasheet specifications and adhering to basic PCB layout and signal integrity practices, integration is straightforward and reliable.

ICGOODFIND: The Microchip 93LC66BT-I/ST is a highly reliable, low-power serial EEPROM ideal for storing configuration data, calibration constants, and event logs. Its simple 3-wire interface and small package offer a perfect balance of functionality and space efficiency for a vast range of embedded applications.

Keywords: Microwire Serial Interface, Non-volatile Memory, Low Power Consumption, Application Circuit Design, Data Retention