FM93CS66LM8 EEPROM 4Kbit Microwire Equivalent & Substitute Parts

Part Overview

The FM93CS66LM8 is a 4Kbit non-volatile EEPROM memory IC manufactured by onsemi, featuring Microwire serial interface protocol and 8-SOIC surface mount packaging. This device is classified as obsolete, making equivalent and substitute parts necessary for ongoing production and maintenance applications. The part operates across a 2.7V to 5.5V supply voltage range with a 250 kHz clock frequency and 15ms write cycle time.

Key Parameters

Parameter	FM93CS66LM8 Specification
Memory Size	4Kbit
Memory Organization	256 x 16
Memory Interface	Microwire
Clock Frequency	250 kHz
Write Cycle Time	15ms
Voltage Supply Range	2.7V ~ 5.5V
Operating Temperature	0°C ~ 70°C
Package / Case	8-SOIC (0.154", 3.90mm Width)
Mounting Type	Surface Mount
Product Status	Obsolete
RoHS Status	RoHS non-compliant

Substitute Part Grouping Explanation

Substitution for the FM93CS66LM8 is determined by the following critical parameters: memory size (4Kbit), memory organization (256 x 16), package type (8-SOIC), and mounting method (surface mount). These parameters establish the physical and functional compatibility baseline.

Substitute parts are grouped into two categories based on interface protocol:

Category 1: Microwire Interface Substitutes — Parts maintaining the original Microwire serial interface protocol, ensuring direct protocol compatibility with existing circuit designs.

Category 2: SPI Interface Substitutes — Parts utilizing SPI (Serial Peripheral Interface) protocol instead of Microwire. These require interface protocol verification during design integration but offer enhanced performance characteristics and active product status.

All substitute candidates maintain the 8-SOIC package specification and surface mount configuration, ensuring mechanical and thermal compatibility.

Parameter Comparison

Parameter	FM93CS66LM8	93LC66B-I/SN	M93C66-RMN3TP/K	M93S66-WMN6P	M93S66-WMN6TP
Manufacturer	onsemi	Microchip Technology	STMicroelectronics	STMicroelectronics	STMicroelectronics
Memory Size	4Kbit	4Kbit	4Kbit	4Kbit	4Kbit
Memory Organization	256 x 16	256 x 16	512 x 8, 256 x 16	256 x 16	256 x 16
Memory Interface	Microwire	Microwire	Microwire	SPI	SPI
Clock Frequency	250 kHz	2 MHz	2 MHz	2 MHz	2 MHz
Write Cycle Time	15ms	6ms	5ms	5ms	5ms
Voltage Supply Range	2.7V ~ 5.5V	2.5V ~ 5.5V	1.8V ~ 5.5V	2.5V ~ 5.5V	2.5V ~ 5.5V
Operating Temperature	0°C ~ 70°C	-40°C ~ 85°C	-40°C ~ 125°C	-40°C ~ 85°C	-40°C ~ 85°C
Package / Case	8-SOIC	8-SOIC	8-SOIC	8-SOIC	8-SOIC
Product Status	Obsolete	Active	Active	Active	Not For New Designs
RoHS Status	RoHS non-compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

For Direct Protocol Compatibility (Microwire Interface):

The 93LC66B-I/SN (Microchip Technology) is the primary substitute for applications requiring Microwire interface continuity. This part maintains active product status, carries ROHS3 compliance, and provides verified programmability. The extended operating temperature range (-40°C to 85°C) and improved write cycle time (6ms versus 15ms) represent performance enhancements over the obsolete FM93CS66LM8.

The M93C66-RMN3TP/K (STMicroelectronics) offers the widest operating temperature range (-40°C to 125°C) and lowest write cycle time (5ms), with automotive-grade qualification (AEC-Q100) and ROHS3 compliance. This part is suitable for applications requiring extended temperature operation or automotive-grade reliability.

For SPI Interface Applications:

The M93S66-WMN6P (STMicroelectronics) provides active product status with SPI interface protocol, ROHS3 compliance, and 5ms write cycle time. This part is recommended for new designs where SPI protocol integration is feasible.

The M93S66-WMN6TP (STMicroelectronics) carries "Not For New Designs" status and should be reserved for legacy system maintenance only.

Compliance Consideration:

All substitute parts achieve ROHS3 compliance, addressing the RoHS non-compliant status of the obsolete FM93CS66LM8. Selection should prioritize parts with active product status for long-term supply chain stability.

Frequently Asked Questions (FAQ)

Q: Can the FM93CS66LM8 be directly replaced with any of these substitutes?

A: Direct replacement depends on interface protocol requirements. The 93LC66B-I/SN and M93C66-RMN3TP/K maintain Microwire protocol compatibility. The M93S66-WMN6P and M93S66-WMN6TP use SPI protocol and require circuit interface verification before substitution.

Q: What is the primary difference between Microwire and SPI interface substitutes?

A: Microwire substitutes (93LC66B-I/SN, M93C66-RMN3TP/K) maintain the original serial communication protocol, requiring no circuit modifications. SPI substitutes (M93S66-WMN6P, M93S66-WMN6TP) use a different serial protocol and require interface circuit redesign or protocol conversion logic.

Q: Are all substitute parts available in the same 8-SOIC package?

A: Yes. All substitute parts specified use the 8-SOIC (0.154", 3.90mm Width) package, ensuring mechanical and thermal compatibility with the original FM93CS66LM8 footprint.

Q: Which substitute offers the best performance improvement?

A: The M93C66-RMN3TP/K provides the lowest write cycle time (5ms), widest operating temperature range (-40°C to 125°C), and automotive-grade qualification. The 93LC66B-I/SN offers a balanced performance improvement with active product status and verified programmability.

Q: What is the significance of "Not For New Designs" status?

A: Parts marked "Not For New Designs" (M93S66-WMN6TP) are suitable only for maintaining existing products or legacy systems. New product development should utilize parts with "Active" status to ensure long-term supply availability and manufacturer support.

Q: Are RoHS compliance differences significant for substitution?

A: Yes. The FM93CS66LM8 is RoHS non-compliant, while all substitutes are ROHS3 compliant. For applications subject to RoHS regulations or customer requirements, substitution with compliant parts is mandatory.

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