FM93C66N EEPROM 4Kbit Microwire Equivalent & Substitute Parts

Part Overview

The FM93C66N is a 4Kbit EEPROM memory IC manufactured by onsemi, featuring Microwire serial interface protocol with 1 MHz clock frequency. This component is classified as obsolete, making equivalent substitute parts necessary for ongoing system support and new design implementations. The part operates within a 4.5V to 5.5V supply range and is housed in an 8-DIP through-hole package. Substitute parts must maintain functional compatibility across memory capacity, interface protocol, and physical packaging while accommodating operational parameter variations.

Key Parameters

Parameter	FM93C66N
Memory Type	Non-Volatile EEPROM
Memory Size	4Kbit
Memory Organization	256 x 16
Memory Interface	Microwire
Clock Frequency	1 MHz
Voltage Supply Range	4.5V ~ 5.5V
Operating Temperature	0°C ~ 70°C
Package Type	8-DIP (0.300", 7.62mm)
Mounting Type	Through Hole
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitute parts for the FM93C66N are qualified based on the following critical parameters that determine functional interchangeability:

Core Compatibility Requirements:

Memory capacity: 4Kbit (256 x 16 organization)
Interface protocol: Microwire serial interface
Package format: 8-DIP through-hole configuration
Supply voltage compatibility: Minimum 4.5V operation capability

Operational Parameter Flexibility: Substitutes may exceed the original specifications in clock frequency, write cycle time, temperature range, and supply voltage range, provided they maintain backward compatibility with the 4.5V ~ 5.5V operating window and support Microwire protocol at the required data rates.

The three qualified substitutes (93C66B-E/P, 93C66B-I/P, and 93LC66B-I/P) all meet these core requirements while offering enhanced performance characteristics and active product status.

Parameter Comparison

Parameter	FM93C66N (onsemi)	93C66B-E/P (Microchip)	93C66B-I/P (Microchip)	93LC66B-I/P (Microchip)
Memory Size	4Kbit	4Kbit	4Kbit	4Kbit
Memory Organization	256 x 16	256 x 16	256 x 16	256 x 16
Memory Interface	Microwire	Microwire	Microwire	Microwire
Clock Frequency	1 MHz	2 MHz	2 MHz	2 MHz
Write Cycle Time	10ms	2ms	2ms	6ms
Voltage Supply Range	4.5V ~ 5.5V	4.5V ~ 5.5V	4.5V ~ 5.5V	2.5V ~ 5.5V
Operating Temperature	0°C ~ 70°C	-40°C ~ 125°C	-40°C ~ 85°C	-40°C ~ 85°C
Package Type	8-DIP	8-PDIP	8-PDIP	8-PDIP
Product Status	Obsolete	Active	Active	Active
RoHS Compliance	Non-compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

93C66B-E/P Selection Criteria: This substitute offers the widest operating temperature range (-40°C ~ 125°C) and fastest write cycle time (2ms). Active product status with ROHS3 compliance ensures long-term availability and regulatory alignment. Suitable for applications requiring extended temperature operation and rapid write performance.

93C66B-I/P Selection Criteria: Provides identical electrical performance to 93C66B-E/P with a more constrained temperature range (-40°C ~ 85°C). Active product status and ROHS3 compliance support modern design requirements. Highest inventory availability (7627 units) among substitutes. Recommended for standard industrial temperature applications.

93LC66B-I/P Selection Criteria: Extends supply voltage compatibility to 2.5V minimum, enabling operation in low-voltage system designs. Maintains 2 MHz clock frequency and active product status with ROHS3 compliance. Write cycle time of 6ms represents a middle ground between the original part and faster alternatives. Largest inventory availability (19527 units) provides supply security.

All three substitutes maintain Microwire protocol compatibility, 4Kbit capacity, and 8-DIP package format required for direct functional replacement.

Frequently Asked Questions (FAQ)

Q: Can FM93C66N be directly replaced with any of these substitutes without circuit modification?

A: Yes. All three substitutes maintain identical memory capacity (4Kbit), organization (256 x 16), Microwire interface protocol, and 8-DIP package format. The 4.5V ~ 5.5V supply voltage range of the original part is fully supported by all substitutes. Pin-to-pin compatibility is maintained across all qualified parts.

Q: What is the primary difference between 93C66B and 93LC66B variants?

A: The 93LC66B variant extends the minimum supply voltage to 2.5V, enabling operation in low-voltage applications. Both variants maintain identical 4Kbit capacity and Microwire interface. The 93LC66B write cycle time is 6ms compared to 2ms for 93C66B variants.

Q: Why is the FM93C66N classified as obsolete?

A: Obsolete status indicates the part is no longer manufactured by onsemi. The three Microchip Technology substitutes (93C66B-E/P, 93C66B-I/P, and 93LC66B-I/P) are active products with ongoing production and support.

Q: Are all substitutes RoHS compliant?

A: Yes. All three substitutes carry ROHS3 compliance certification. The original FM93C66N is RoHS non-compliant, making these substitutes necessary for applications requiring regulatory compliance.

Q: Which substitute offers the best write performance?

A: Both 93C66B variants (93C66B-E/P and 93C66B-I/P) provide 2ms write cycle time, compared to 10ms for the original part and 6ms for 93LC66B-I/P.

Q: What is the temperature operating range difference?

A: The original FM93C66N operates 0°C ~ 70°C. The 93C66B-E/P extends to -40°C ~ 125°C. Both 93C66B-I/P and 93LC66B-I/P operate -40°C ~ 85°C. Selection depends on specific application temperature requirements.

Q: Can 93LC66B-I/P be used in 5V-only systems?

A: Yes. The 93LC66B-I/P supply voltage range is 2.5V ~ 5.5V, fully encompassing 5V operation. The extended lower voltage limit provides additional flexibility for mixed-voltage system designs.

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