Microchip Technology 93C66A-I/ST

Overview

93C66A-I/ST from Microchip Technology Inc. is a 4 Kbit (512 × 8-bit) low-voltage serial EEPROM with Microwire-compatible 3-wire interface, 4.5–5.5 V supply range, and industrial temperature grade (–40°C to +85°C). It features self-timed erase/write cycles, automatic ERAL before WRAL, power-on/off data protection, and Ready/Busy status signaling via DO pin - used in embedded system configuration storage and calibration data retention.

For engineers reviewing the 93C66A-I/ST datasheet, 93C66A-I/ST pinout, 93C66A-I/ST application, or 93C66A-I/ST equivalent, key selection criteria include its fixed 8-bit organization (no ORG pin), 2 ms typical write cycle time, 1 million endurance cycles, 200-year data retention, and compatibility with legacy Microwire controllers in space-constrained industrial control modules.

Technical Context

The 93C66A-I/ST implements a synchronous serial interface using CS, CLK, and DI/DO lines with start-bit detection and opcode-based command execution. Its internal architecture includes an address decoder, mode decode logic, and output buffer, supporting READ, WRITE, ERASE, ERAL, WRAL, EWEN, and EWDS instructions - all executed with precise timing per AC specs (e.g., TWC = 2 ms, TPD ≤ 400 ns).

Unlike C-variant devices, the 93C66A has no ORG pin (NC), enforcing fixed 8-bit word organization. Write initiation occurs on the rising edge of CLK at the last data bit, and VCC must be ≥4.5 V for ERAL/WRAL operations. Power-on reset disables erase/write until explicit EWEN command is issued.

Key Specifications

Pinout & Package

93C66A-I/ST is packaged in an 8-lead SOIC (SOIC-8, package code "ST"), with lead finish Pb-free (Matte Tin). Pin 1 is CS, pin 2 is CLK, pin 3 is DI, pin 4 is DO, pin 5 is VSS, pin 6 is NC (no internal connection - replaces ORG pin found only on C-variants), pin 7 is NC, and pin 8 is VCC.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar serial EEPROM applications.

Compared with 93LC66A-I/ST and AT25040B-MAU-1.8, the 93C66A-I/ST delivers deterministic 5 V-only operation with hardware-ready signaling - ideal for legacy industrial designs where voltage stability and minimal MCU intervention are prioritized over multi-voltage flexibility or SPI integration.

Availability

93C66A-I/ST is available at Aetrix Electronics and suitable for industrial sensor calibration, embedded system configuration, and motor drive parameter storage requiring stable component supply across extended production lifecycles.

Supply support for 93C66A-I/ST includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Microchip Technology Inc. is a leading provider of microcontrollers, analog components, and memory solutions, headquartered in Chandler, Arizona.

The 93C66A belongs to Microchip's legacy 93XX serial EEPROM product line, designed specifically for cost-sensitive, space-constrained industrial and automotive applications requiring reliable nonvolatile storage with minimal external components and proven Microwire interoperability.

FAQ

What is the function of the NC pins on the 93C66A-I/ST?

The 93C66A-I/ST has two NC (No Connection) pins - pin 6 and pin 7 - which are physically present but internally unconnected. These replace the ORG pin (used only on C-variant devices) and an additional NC in other packages. They must remain unconnected or tied to VSS/VCC per layout guidelines; neither affects device operation nor timing.

Does the 93C66A-I/ST require an EWEN command before every write operation?

Yes. The 93C66A-I/ST powers up in Erase/Write Disable (EWDS) mode. An EWEN command must be issued before any ERASE or WRITE instruction can execute. After a successful write, best practice is to issue EWDS to prevent accidental modification - a requirement explicitly stated in the datasheet for data integrity.

What is the maximum clock frequency supported by the 93C66A-I/ST?

The 93C66A-I/ST supports up to 3 MHz clock frequency when VCC is 4.5–5.5 V. This is specified in Table 1-2 (A1) of DS21795E. At lower voltages, maximum frequency decreases - but since 93C66A requires ≥4.5 V, 3 MHz is the operational ceiling for this variant.

Can the 93C66A-I/ST be used in automotive applications?

No. The 93C66A-I/ST is rated for Industrial temperature range (–40°C to +85°C), denoted by the "I" suffix. Automotive-grade versions (e.g., 93C66A-E/ST) carry "E" suffix and are qualified to –40°C to +125°C. Using the "I" version in under-hood automotive environments violates thermal specifications and voids reliability guarantees.

How does the Ready/Busy status work on the DO pin of the 93C66A-I/ST?

During an erase or write cycle, the DO pin outputs Ready/Busy status: logic low indicates ongoing programming; logic high means completion. To read status, CS must be brought high for ≥250 ns after TCSL - then sample DO. Issuing a Start bit followed by CS low clears the status flag. DO returns to High-Z when CS is low or during non-status phases.