FM75M8X Equivalent & Substitute Parts

Part Overview

The FM75M8X is a digital temperature sensor manufactured by onsemi, designed for local temperature measurement across the -40°C to 125°C range with 11-bit resolution and SMBus output. The device is currently obsolete, making equivalent and substitute parts necessary for ongoing system support, redesigns, and new production requirements. This reference provides direct and functional alternatives that maintain compatibility within the specified electrical and mechanical parameters.

Key Parameters

Parameter	FM75M8X
Sensor Type	Digital, Local
Sensing Temperature Range	-40°C ~ 125°C
Output Type	SMBus
Voltage Supply	2.7V ~ 5.5V
Resolution	11 bits
Accuracy (Best/Worst)	±2°C / ±4°C
Package	8-SOIC (0.154", 3.90mm Width)
Mounting Type	Surface Mount
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution for the FM75M8X is determined by the following critical parameters: package type (8-SOIC), mounting method (surface mount), supply voltage compatibility (2.7V ~ 5.5V), output protocol (SMBus/I2C), resolution (11 bits), and operating temperature range (-40°C minimum to 125°C maximum). Parts are grouped into three categories:

Direct Manufacturer Substitute: NCT75DR2G maintains the same package and form factor with extended temperature range (-55°C ~ 125°C) and enhanced resolution (12 bits), offering improved performance within the same physical constraints.

Upgrade Substitutes: DS75S+ and DS75S+T&R provide identical electrical specifications to the FM75M8X with extended lower temperature limit (-55°C vs -40°C), active product status, and RoHS3 compliance. These differ only in packaging format (Tube vs Cut Tape & Digi-Reel).

Similar Functional Alternatives: DS1621S+, DS1621S+T&R, DS1631Z+, DS1631Z+T&R, DS1721S+, DS1721S+T&R, and DS75LVS+ maintain the 8-SOIC package and core functionality with variations in resolution, accuracy, and feature sets. DS75LVS+ operates at reduced supply voltage (1.7V ~ 3.7V).

Parameter Comparison

Part Number	Manufacturer	Status	Temp Range (°C)	Resolution (bits)	Output Type	Supply Voltage	Accuracy Best/Worst	Package	Packaging Format
FM75M8X	onsemi	Obsolete	-40 ~ 125	11	SMBus	2.7V ~ 5.5V	±2°C / ±4°C	8-SOIC	—
NCT75DR2G	onsemi	Active	-55 ~ 125	12	I2C/SMBus	3V ~ 5.5V	±1°C / ±3°C	8-SOIC	Cut Tape & Digi-Reel
DS75S+	Analog Devices Inc./Maxim Integrated	Active	-55 ~ 125	11	I2C	2.7V ~ 5.5V	±2°C / ±3°C	8-SOIC	Tube
DS75S+T&R	Analog Devices Inc./Maxim Integrated	Active	-55 ~ 125	11	I2C	2.7V ~ 5.5V	±2°C / ±3°C	8-SOIC	Cut Tape & Digi-Reel
DS1621S+	Analog Devices Inc./Maxim Integrated	Active	-55 ~ 125	9	I2C	2.7V ~ 5.5V	±0.5°C / ±2°C	8-SOIC	Tube
DS1621S+T&R	Analog Devices Inc./Maxim Integrated	Active	-55 ~ 125	9	I2C	2.7V ~ 5.5V	±0.5°C / ±2°C	8-SOIC	Cut Tape & Digi-Reel
DS1631Z+	Analog Devices Inc./Maxim Integrated	Active	-55 ~ 125	11	I2C	2.7V ~ 5.5V	±0.5°C / ±2°C	8-SOIC	Tube
DS1631Z+T&R	Analog Devices Inc./Maxim Integrated	Active	-55 ~ 125	11	I2C	2.7V ~ 5.5V	±0.5°C / ±2°C	8-SOIC	Cut Tape & Digi-Reel
DS1721S+	Analog Devices Inc./Maxim Integrated	Active	-55 ~ 125	11	I2C	2.7V ~ 5.5V	±1°C / ±2°C	8-SOIC	Tube
DS1721S+T&R	Analog Devices Inc./Maxim Integrated	Active	-55 ~ 125	11	I2C	2.7V ~ 5.5V	±1°C / ±2°C	8-SOIC	Cut Tape
DS75LVS+	Analog Devices Inc./Maxim Integrated	Active	-55 ~ 125	11	I2C	1.7V ~ 3.7V	±2°C / ±3°C	8-SOIC	Tube

Engineering Selection Recommendations

For Direct Replacement (Highest Compatibility): DS75S+ and DS75S+T&R are the primary substitutes, offering identical 11-bit resolution and 2.7V ~ 5.5V supply voltage range as the FM75M8X. Both maintain active product status and RoHS3 compliance. The choice between Tube and Cut Tape & Digi-Reel packaging depends on procurement and assembly requirements. DS75S+T&R provides higher inventory availability (48,300 units).

For Enhanced Performance: NCT75DR2G provides 12-bit resolution and improved accuracy (±1°C best case vs ±2°C) with active status and RoHS3 compliance. Note that supply voltage minimum is 3V rather than 2.7V, requiring verification against system requirements.

For Superior Accuracy Requirements: DS1631Z+ and DS1631Z+T&R deliver ±0.5°C best-case accuracy with 11-bit resolution, matching the FM75M8X resolution while providing significantly tighter tolerance. Both are RoHS3 compliant and active products.

For Cost-Optimized Alternatives: DS1621S+ and DS1621S+T&R offer reduced resolution (9 bits) but superior accuracy (±0.5°C best case) and active product status with RoHS3 compliance.

For Low-Voltage Applications: DS75LVS+ operates at 1.7V ~ 3.7V supply voltage, suitable only for systems with reduced power budgets that do not require the standard 2.7V ~ 5.5V range.

All substitute parts maintain the 8-SOIC package form factor and surface mount compatibility. Protocol differences (SMBus vs I2C) require firmware verification, as I2C is a subset of SMBus functionality.

Frequently Asked Questions (FAQ)

Q: Can DS75S+ directly replace FM75M8X without firmware changes? A: DS75S+ maintains I2C protocol compatibility with SMBus, as I2C is functionally compatible with SMBus at the register level. However, system firmware must be verified to confirm I2C command set compatibility with the original SMBus implementation.

Q: What is the difference between DS75S+ and DS75S+T&R? A: Both parts are electrically identical. DS75S+ is supplied in Tube packaging, while DS75S+T&R is supplied in Cut Tape & Digi-Reel format. Selection depends on assembly line requirements and procurement preferences.

Q: Why does NCT75DR2G have a 3V minimum supply voltage instead of 2.7V? A: NCT75DR2G is a different product line with enhanced specifications (12-bit resolution, ±1°C accuracy). Systems operating at 2.7V ~ 3V must verify compatibility or select alternative parts such as DS75S+ that maintain the 2.7V minimum.

Q: Is DS1631Z+ suitable for applications requiring 11-bit resolution? A: Yes. DS1631Z+ provides 11-bit resolution identical to FM75M8X with superior accuracy (±0.5°C vs ±2°C). It is RoHS3 compliant and actively produced.

Q: What is the impact of resolution differences between 9-bit and 11-bit sensors? A: 11-bit resolution provides 0.0625°C per LSB, while 9-bit resolution provides 0.25°C per LSB. Applications requiring finer temperature discrimination must use 11-bit alternatives (DS75S+, DS1631Z+, DS1721S+, or NCT75DR2G).

Q: Are all substitute parts RoHS3 compliant? A: Yes. All active substitute parts listed (NCT75DR2G, DS75S+, DS75S+T&R, DS1621S+, DS1621S+T&R, DS1631Z+, DS1631Z+T&R, DS1721S+, DS1721S+T&R, and DS75LVS+) are RoHS3 compliant.

Q: Can DS75LVS+ be used in systems designed for 2.7V ~ 5.5V operation? A: No. DS75LVS+ operates at 1.7V ~ 3.7V and is not suitable for systems requiring 5.5V supply voltage. Use DS75S+, DS75S+T&R, or other alternatives that support the full 2.7V ~ 5.5V range.

Q: What packaging formats are available for high-volume production? A: Cut Tape & Digi-Reel format is available for NCT75DR2G, DS75S+T&R, DS1621S+T&R, DS1631Z+T&R, and DS1721S+T&R, with inventory levels ranging from 3,578 to 48,300 units.

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