Microchip 93LC86-I/SN 1K SPI Serial EEPROM: Features and Application Design Guide
The Microchip 93LC86-I/SN is a 16-Kbit (1K x 16 or 2K x 8) Serial Electrically Erasable PROM (EEPROM) that utilizes the popular Serial Peripheral Interface (SPI) bus for communication. Housed in a compact 8-pin SOIC package, this non-volatile memory IC is engineered for reliability, low power consumption, and ease of integration into a vast array of embedded systems. It serves as a critical component for storing configuration data, calibration constants, and other vital information that must be retained when system power is removed.
Key Features and Specifications
The 93LC86 boasts a set of features that make it a versatile choice for designers:
SPI-Compatible Serial Interface: Supports clock frequencies up to 3 MHz, enabling high-speed data transfer and simplifying communication with a wide range of microcontrollers and processors.
Wide Voltage Operation: It operates over a broad voltage range (2.5V to 5.5V), making it suitable for both 3.3V and 5V systems without the need for level shifters.
Low-Power Consumption: The device is designed for power-sensitive applications, featuring a low standby current and an active read current of just 1 mA (typical at 5V).
Hardware and Software Protection: It includes built-in write-protection mechanisms. A dedicated `WP` (Write Protect) pin and specific instruction codes allow the memory array to be locked against inadvertent writes, safeguarding critical data.
High Reliability: With an endurance of 1 million erase/write cycles and data retention of over 200 years, it ensures data integrity for the lifetime of the product.
Sequential Read Capability: Allows for efficient continuous read operations of the entire memory array, maximizing data throughput.
Temperature Range: The industrial-grade `-I` suffix denotes an operating temperature range of -40°C to +85°C, ensuring robust performance in harsh environments.
Application Design Guide
Integrating the 93LC86 into a design is straightforward, but attention to a few key areas will ensure optimal performance.
1. Interface Connection:
The SPI interface requires four primary signals from the host microcontroller (MCU):
CS (Chip Select): Driven low by the MCU to select and initiate communication with the EEPROM.
SCK (Serial Clock): Provides the synchronization clock for data input and output.
SI (Serial Input)/MOSI: The line for transferring instruction and data bits from the MCU to the EEPROM.
SO (Serial Output)/MISO: The line for transferring data bits from the EEPROM back to the MCU.
The `HOLD` pin can be used to pause serial communication without deselecting the device, and the `WP` pin must be tied high to enable writing or can be controlled by the MCU for dynamic protection.
2. Communication Protocol:
All operations are initiated by first pulling the `CS` line low. The MCU then sends an 8-bit instruction opcode (e.g., `WREN` for Write Enable, `READ` for Read, `WRITE` for Write) followed by a 16-bit address (for 2K x 8 mode; 15-bit for 1K x 16 mode) if applicable. For a write operation, the data byte or word follows. It is crucial to ensure the `WP` pin is inactive (high) and that the `WREN` instruction has been sent prior to any write or erase command to enable the write latch.
3. Write Cycle Timing:
A critical aspect of EEPROM operation is the write cycle time. After receiving a `WRITE` instruction, the part enters an internally timed write cycle (`t_WC`), typically 3-5 ms, during which it will not respond to any commands. The MCU must wait for this duration before attempting to communicate again. Polling the device's status by reading the `SO` pin after issuing a `WRITE` instruction can determine when the cycle is complete and the device is ready.
4. PCB Layout Considerations:
To maintain signal integrity, especially at higher clock speeds:
Keep the SPI trace lengths short.
Use pull-up resistors on the `CS`, `SO`, and `WP` lines if they are susceptible to noise.
Place a 100nF decoupling capacitor close to the `VCC` and `GND` pins of the IC to filter power supply noise.
5. Typical Applications:
Consumer Electronics: Storing user settings, channel lists, and last-state data in appliances, TVs, and audio equipment.
Automotive: Holding calibration data for sensors and instrument clusters, and storing fault codes.
Industrial Systems: Safeguarding configuration parameters for programmable logic controllers (PLCs), motor drives, and smart meters.
Medical Devices: Retaining device calibration and usage data securely.
The Microchip 93LC86-I/SN is a robust, highly reliable, and easy-to-use serial EEPROM solution. Its combination of a standard SPI interface, wide voltage range, extensive write-protection features, and industrial temperature range makes it an excellent choice for designers across automotive, industrial, and consumer markets who need dependable non-volatile memory in a minimal footprint.
Keywords:
SPI EEPROM, Non-volatile Memory, Write Protection, Embedded Systems, Microchip 93LC86
