LM3674MFX-1.2 Equivalent & Substitute Parts

Part Overview

The LM3674MFX-1.2 is a buck switching regulator IC from Texas Instruments, delivering a fixed 1.2V output at 600mA with input voltage range of 2.7V to 5.5V. This component is classified as obsolete, which necessitates identification of active equivalent parts for new designs and ongoing production requirements. The part operates at 2MHz switching frequency with integrated synchronous rectification in a compact SC-74A (SOT-753) surface mount package.

Key Parameters

Parameter	Value
Function	Step-Down (Buck)
Output Configuration	Positive
Output Type	Fixed
Number of Outputs	1
Voltage - Input (Min)	2.7V
Voltage - Input (Max)	5.5V
Voltage - Output (Fixed)	1.2V
Current - Output	600mA
Frequency - Switching	2MHz
Synchronous Rectifier	Yes
Operating Temperature	-30°C ~ 85°C (TA)
Mounting Type	Surface Mount
Package / Case	SC-74A, SOT-753
Supplier Device Package	SOT-23-5
RoHS Status	RoHS non-compliant
Moisture Sensitivity Level (MSL)	1 (Unlimited)

Substitute Part Grouping Explanation

Substitution of the LM3674MFX-1.2 is determined by strict alignment of the following electrical and mechanical parameters:

Critical Matching Parameters:

Output voltage: 1.2V fixed
Output current capability: minimum 600mA
Input voltage range: 2.7V to 5.5V minimum
Topology: Buck switching regulator
Output configuration: Positive, single output
Synchronous rectification: Required
Package compatibility: SOT-23-5 form factor (SC-74A or TSOT-23-5 variants)
Mounting type: Surface mount

Substitution Categories:

Direct Equivalent (Same Manufacturer): LM3674MFX-1.2/NOPB maintains identical electrical specifications with improved product status (Active) and RoHS3 compliance.
Functional Equivalents (Active Status): ADP2108AUJZ-1.2-R7, MCP1603T-120I/OS, RT8009-12GJ5, and RT8009-12GB meet or exceed the core electrical requirements while offering active product status and modern compliance certifications.
Parameter Variations: Some substitutes exhibit minor deviations in switching frequency (1.25MHz to 3MHz), operating temperature range, or output current (500mA to 600mA), which remain functionally compatible within the application envelope defined by the original part specifications.

Parameter Comparison

Parameter	LM3674MFX-1.2	LM3674MFX-1.2/NOPB	ADP2108AUJZ-1.2-R7	MCP1603T-120I/OS	RT8009-12GB	RT8009-12GJ5
Manufacturer	Texas Instruments	Texas Instruments	Analog Devices Inc.	Microchip Technology	Richtek USA Inc.	Richtek USA Inc.
Product Status	Obsolete	Active	Active	Active	Active	Active
Function	Step-Down	Step-Down	Step-Down	Step-Down	Step-Down	Step-Down
Output Voltage (Fixed)	1.2V	1.2V	1.2V	1.2V	1.2V	1.2V
Current - Output	600mA	600mA	600mA	500mA	600mA	600mA
Voltage - Input (Min)	2.7V	2.7V	2.3V	2.7V	2.5V	2.5V
Voltage - Input (Max)	5.5V	5.5V	5.5V	5.5V	5.5V	5.5V
Frequency - Switching	2MHz	2MHz	3MHz	2MHz	1.25MHz	1.25MHz
Synchronous Rectifier	Yes	Yes	Yes	Yes	Yes	Yes
Operating Temperature	-30°C ~ 85°C (TA)	-30°C ~ 85°C (TA)	-40°C ~ 125°C (TA)	-40°C ~ 125°C (TJ)	-40°C ~ 85°C (TA)	-40°C ~ 85°C (TA)
Package / Case	SC-74A, SOT-753	SC-74A, SOT-753	SOT-23-5 Thin, TSOT-23-5	SOT-23-5 Thin, TSOT-23-5	SC-74A, SOT-753	SOT-23-5 Thin, TSOT-23-5
Supplier Device Package	SOT-23-5	SOT-23-5	TSOT-23-5	TSOT-23-5	SOT-23-5	TSOT-23-5
RoHS Status	RoHS non-compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Moisture Sensitivity Level (MSL)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	3 (168 Hours)	3 (168 Hours)

Engineering Selection Recommendations

Primary Recommendation: LM3674MFX-1.2/NOPB

This part is the direct equivalent from Texas Instruments with identical electrical specifications. It maintains the same 2MHz switching frequency, 600mA output current, and SOT-23-5 package footprint. The transition from obsolete to active product status and achievement of ROHS3 compliance make this the preferred choice for design continuity with minimal risk.

Secondary Recommendations:

ADP2108AUJZ-1.2-R7 (Analog Devices Inc.): Suitable for applications requiring extended operating temperature range (-40°C to 125°C). The 3MHz switching frequency may reduce output filter component size. Input voltage minimum of 2.3V provides broader input compatibility. ROHS3 compliant with unlimited MSL rating.

RT8009-12GJ5 (Richtek USA Inc.): Offers 600mA output current with ROHS3 compliance and active product status. The 1.25MHz switching frequency may require larger output filter components compared to the original 2MHz design. TSOT-23-5 package variant available. MSL rating of 3 requires standard moisture control during assembly.

MCP1603T-120I/OS (Microchip Technology): Provides active product status and extended temperature range (-40°C to 125°C). Output current is rated at 500mA, which is 83% of the original specification. Suitable only for applications where 500mA output current is sufficient. ROHS3 compliant with unlimited MSL.

Compliance Considerations:

All recommended substitutes achieve ROHS3 compliance, addressing regulatory requirements that the obsolete LM3674MFX-1.2 does not meet. Selection should account for MSL requirements during manufacturing; parts with MSL 1 (unlimited) require no special moisture control, while MSL 3 parts require baking and controlled storage.

Frequently Asked Questions (FAQ)

Q: Can I use MCP1603T-120I/OS as a direct replacement if my application requires 600mA output?

A: No. The MCP1603T-120I/OS is rated for 500mA maximum output current, which is below the 600mA specification of the LM3674MFX-1.2. Use this part only if your application current requirement is 500mA or less.

Q: What is the difference between SC-74A and TSOT-23-5 packages?

A: Both are SOT-23-5 form factors with identical pin configurations and PCB footprints. SC-74A and SOT-753 refer to the standard SOT-23-5 package, while TSOT-23-5 designates a thin variant. They are mechanically and electrically interchangeable on the same PCB layout.

Q: Does the switching frequency difference between 1.25MHz and 3MHz affect circuit design?

A: Yes. Switching frequency impacts output filter design. Lower frequencies (1.25MHz) require larger inductors and capacitors to achieve the same output ripple voltage. Higher frequencies (3MHz) allow smaller filter components. The original design must be re-evaluated if switching frequency changes significantly.

Q: Why is LM3674MFX-1.2/NOPB preferred over other substitutes?

A: It is the direct manufacturer equivalent with identical electrical specifications, same switching frequency, and same output current rating. This minimizes design re-validation and component re-qualification risk. The transition from obsolete to active status ensures long-term availability.

Q: Are there any thermal or reliability differences between these substitutes?

A: Operating temperature ranges vary. ADP2108AUJZ-1.2-R7 and MCP1603T-120I/OS support -40°C to 125°C, while RT8009 variants and the original LM3674 support -40°C to 85°C or -30°C to 85°C. Extended temperature range parts may offer improved reliability in extreme environments. MSL ratings differ; MSL 1 parts require no moisture control, while MSL 3 parts require standard baking procedures.

Q: Can I substitute based on package type alone?

A: No. Package compatibility is necessary but not sufficient. Electrical parameters including output voltage, output current, input voltage range, and switching frequency must all match or exceed the original specification. Verify all parameters before substitution.

Q: What does ROHS3 compliance mean for this part?

A: ROHS3 compliance indicates the part meets Restriction of Hazardous Substances Directive requirements, restricting lead, cadmium, mercury, and other hazardous materials. This is a regulatory requirement for many markets. The obsolete LM3674MFX-1.2 is non-compliant; all recommended substitutes are ROHS3 compliant.

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