LM3670MFX-1.2 Equivalent & Substitute Parts

Part Overview

The LM3670MFX-1.2 is a buck switching regulator IC from Texas Instruments, delivering a fixed 1.2V output at 350mA with a 1MHz switching frequency. This part is classified as obsolete, making equivalent and substitute parts necessary for new designs and production continuity. The device operates across a 2.5V to 5.5V input range with synchronous rectification and is housed in a SC-74A (SOT-753) package suitable for surface mount applications.

Substiute Parts

LM3670MFX-1.2

Texas InstrumentsIn Stock: 10387LM3670MFX-1.2 Datasheet

Current PartRFQ

LM3670MFX-1.2/NOPB

Texas InstrumentsIn Stock: 1400LM3670MFX-1.2/NOPB Datasheet

DirectRFQ

ADP2108AUJZ-1.2-R7

Analog Devices Inc.In Stock: 18099ADP2108AUJZ-1.2-R7 Datasheet

MFR RecommendedRFQ

MCP1603T-120I/OS

Microchip TechnologyIn Stock: 4498MCP1603T-120I/OS Datasheet

MFR RecommendedRFQ

RT8009-12GB

Richtek USA Inc.In Stock: 4552RT8009-12GB Datasheet

MFR RecommendedRFQ

RT8009-12GJ5

Richtek USA Inc.In Stock: 18840RT8009-12GJ5 Datasheet

MFR RecommendedRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution eligibility for the LM3670MFX-1.2 is determined by the following critical parameters:

Fixed Substitution Criteria:

• Output voltage: 1.2V (fixed)
• Output configuration: Positive
• Topology: Buck (step-down)
• Number of outputs: 1
• Synchronous rectifier: Yes
• Input voltage range: Minimum 2.5V, maximum 5.5V
• Mounting type: Surface Mount
• Package compatibility: SOT-23-5 variants (SC-74A/SOT-753 or TSOT-23-5)

Flexible Parameters (allowing substitution with higher ratings):

• Output current: 350mA minimum (higher current ratings acceptable)
• Switching frequency: 1MHz baseline (higher frequencies acceptable)
• Operating temperature: -40°C to 85°C minimum (extended ranges acceptable)

Substitute parts must maintain identical output voltage and input voltage specifications while meeting or exceeding current delivery capability. Package form factors within the SOT-23-5 family are interchangeable for surface mount applications.

Parameter Comparison

Engineering Selection Recommendations

Direct Replacement (Highest Compatibility): LM3670MFX-1.2/NOPB is the direct successor from Texas Instruments with identical electrical specifications and package form factor. This part maintains the same 350mA output current and 1MHz switching frequency while achieving RoHS3 compliance and active product status. Selection of this part eliminates design re-qualification requirements.

Higher Current Capacity Substitutes: ADP2108AUJZ-1.2-R7 (Analog Devices), MCP1603T-120I/OS (Microchip), and RT8009-12GJ5 (Richtek) all deliver 500mA to 600mA output current, exceeding the original 350mA specification. These parts maintain the 1.2V fixed output voltage and SOT-23-5 package compatibility. All three are RoHS3 compliant with active product status.

ADP2108AUJZ-1.2-R7 offers the lowest input voltage floor at 2.3V and highest switching frequency at 3MHz, suitable for applications requiring extended input range or reduced component size. MCP1603T-120I/OS provides 500mA at 2MHz with extended operating temperature to 125°C. RT8009-12GJ5 maintains the original 1MHz baseline frequency with 600mA capacity and operates to 85°C.

Compliance Considerations: All active substitute parts achieve RoHS3 compliance, addressing the non-compliant status of the obsolete LM3670MFX-1.2. Selection of any active substitute ensures regulatory alignment for new production.

Frequently Asked Questions (FAQ)

Q: Can I use a substitute part with higher output current rating? A: Yes. The LM3670MFX-1.2 delivers 350mA maximum. Substitute parts rated for 500mA or 600mA are fully compatible and provide design margin. Higher current capacity does not affect circuit operation at lower load currents.

Q: Are all substitute parts pin-compatible? A: All listed substitutes use SOT-23-5 package variants (SC-74A/SOT-753 or TSOT-23-5). Pin assignments are identical across these package types, ensuring direct PCB compatibility without layout modification.

Q: What is the difference between SC-74A and TSOT-23-5 packages? A: Both are SOT-23-5 form factors. SC-74A (SOT-753) is the standard variant; TSOT-23-5 is the thin variant with reduced height. Both are mechanically and electrically interchangeable on standard SOT-23-5 footprints.

Q: Does switching frequency affect circuit design? A: Switching frequency influences output filter component selection. The original 1MHz baseline is maintained by LM3670MFX-1.2/NOPB and RT8009-12GJ5. Higher frequencies (2MHz to 3MHz) in ADP2108AUJZ-1.2-R7 and MCP1603T-120I/OS allow smaller filter inductors and capacitors. Filter redesign may be required for optimal performance with higher-frequency substitutes.

Q: Which substitute offers the widest input voltage range? A: ADP2108AUJZ-1.2-R7 operates from 2.3V minimum input, compared to 2.5V for the original part and most substitutes. MCP1603T-120I/OS requires 2.7V minimum. This difference is significant only in applications with input sources below 2.5V.

Q: Are all substitutes RoHS compliant? A: Yes. All active substitute parts are RoHS3 compliant. The original LM3670MFX-1.2 is RoHS non-compliant. Selection of any substitute addresses regulatory requirements for new designs.

Q: Can I use RT8009-12GB instead of RT8009-12GJ5? A: Both are Richtek RT8009 variants with identical electrical specifications and 1.2V output. RT8009-12GB uses SC-74A (SOT-753) package; RT8009-12GJ5 uses TSOT-23-5 package. Selection depends on PCB footprint requirements. Both are electrically interchangeable.