LM317MSTT3 Linear Voltage Regulator Equivalent & Substitute Parts

Part Overview

The LM317MSTT3 is a positive adjustable linear voltage regulator IC rated for 500mA output current in SOT-223 (TO-261) surface mount packaging. This component is classified as obsolete, which necessitates identification of active equivalent and substitute parts for ongoing design support and procurement. The LM317 base product family offers multiple variants across manufacturers with varying output current ratings and compliance certifications that serve as functional alternatives.

Key Parameters

Parameter	LM317MSTT3
Manufacturer	onsemi
Output Configuration	Positive
Output Type	Adjustable
Number of Regulators	1
Voltage - Input (Max)	40V
Voltage - Output (Min/Fixed)	1.2V
Voltage - Output (Max)	37V
Current - Output	500mA
Current - Quiescent (Iq)	10 mA
PSRR	80dB ~ 65dB (120Hz)
Protection Features	Over Current, Over Temperature, Short Circuit
Operating Temperature	0°C ~ 125°C (TJ)
Mounting Type	Surface Mount
Package / Case	TO-261-4, TO-261AA
Supplier Device Package	SOT-223 (TO-261)
Product Status	Obsolete
RoHS Status	RoHS non-compliant
Moisture Sensitivity Level (MSL)	1 (Unlimited)

Substitute Part Grouping Explanation

Substitution of the LM317MSTT3 is determined by the following critical parameters:

Electrical Compatibility Requirements:

Output configuration (Positive)
Output type (Adjustable)
Voltage input maximum (40V)
Voltage output range (1.2V to 37V minimum/maximum)
Current output rating (500mA or higher)
Protection features (Over Current, Over Temperature, Short Circuit)

Mechanical Compatibility Requirements:

Mounting type (Surface Mount)
Package case (TO-261-4, TO-261AA)
Supplier device package (SOT-223 or SOT-223-4)

Compliance Considerations:

Product status (Active preferred over Obsolete)
RoHS compliance status
Moisture sensitivity level

Substitute parts are classified into two categories:

Direct Substitutes: Parts with identical electrical specifications (500mA output current) and matching package designations.

Similar Substitutes: Parts with enhanced output current ratings (1.5A) that maintain electrical and mechanical compatibility while providing higher current capability. These parts are pin-compatible and functionally superior for applications requiring additional current headroom.

Parameter Comparison

Part Number	Manufacturer	Output Current	Voltage Input (Max)	Voltage Output (Min)	Voltage Output (Max)	Operating Temp	Product Status	RoHS Status	Package	Inventory
LM317MSTT3	onsemi	500mA	40V	1.2V	37V	0°C ~ 125°C	Obsolete	RoHS non-compliant	SOT-223	1025 Pcs
LM317MSTT3G	onsemi	500mA	40V	1.2V	37V	0°C ~ 125°C	Active	ROHS3 Compliant	SOT-223	40300 Pcs
LM317MDCYR	Texas Instruments	500mA	40V	1.25V	37V	-40°C ~ 125°C	Active	ROHS3 Compliant	SOT-223-4	12300 Pcs
LM317AEMP/NOPB	Texas Instruments	1.5A	40V	1.25V	37V	-40°C ~ 125°C	Active	ROHS3 Compliant	SOT-223-4	15300 Pcs
LM317AEMPX/NOPB	Texas Instruments	1.5A	40V	1.25V	37V	-40°C ~ 125°C	Active	ROHS3 Compliant	SOT-223-4	5000400 Pcs
LM317DCY	Texas Instruments	1.5A	40V	1.25V	37V	0°C ~ 125°C	Active	ROHS3 Compliant	SOT-223-4	1000400 Pcs
LM317DCYG3	Texas Instruments	1.5A	40V	1.25V	37V	0°C ~ 125°C	Active	ROHS3 Compliant	SOT-223-4	33200 Pcs
LM317DCYR	UMW	1.5A	40V	1.2V	37V	0°C ~ 125°C	Active	ROHS3 Compliant	SOT-223	12200 Pcs
LM317DCYRG3	Texas Instruments	1.5A	40V	1.25V	37V	0°C ~ 125°C	Active	ROHS3 Compliant	SOT-223-4	33200 Pcs
LM317EMP/NOPB	Texas Instruments	1.5A	37V	1.25V	37V	0°C ~ 125°C	Active	ROHS3 Compliant	SOT-223-4	3732 Pcs
LM317EMPX/NOPB	Texas Instruments	1.5A	37V	1.25V	37V	0°C ~ 125°C	Active	ROHS3 Compliant	SOT-223-4	2200 Pcs

Engineering Selection Recommendations

Direct Equivalent (Recommended Primary Choice):

LM317MSTT3G from onsemi is the direct equivalent with identical electrical specifications and package designation. This part maintains 500mA output current, matching voltage ranges, and protection features. The primary advantage is active product status with ROHS3 compliance, addressing the obsolescence of the original LM317MSTT3. Inventory availability is substantial at 40,300 pieces.

Alternative Direct Equivalent:

LM317MDCYR from Texas Instruments provides 500mA output current with extended operating temperature range (-40°C to 125°C versus 0°C to 125°C). This part is suitable for applications requiring wider temperature operation. ROHS3 compliance and active status are confirmed.

Higher Current Alternatives (1.5A Rating):

For applications where additional current margin is beneficial, the following 1.5A-rated parts are pin-compatible substitutes:

LM317AEMPX/NOPB (Texas Instruments): Highest inventory availability at 5,000,400 pieces with extended temperature range (-40°C to 125°C)
LM317DCYG3 (Texas Instruments): 33,200 pieces available with standard temperature range (0°C to 125°C)
LM317DCYR (UMW): 12,200 pieces available, maintains 1.2V minimum output voltage matching the original specification

All substitute parts maintain ROHS3 compliance and active product status. Selection should prioritize inventory availability, temperature range requirements, and manufacturer preference for supply chain consistency.

Frequently Asked Questions (FAQ)

Q: Can LM317MSTT3G be used as a direct replacement for LM317MSTT3?

A: Yes. LM317MSTT3G is a direct equivalent with identical electrical specifications (500mA output, 1.2V to 37V output range, 40V maximum input) and package designation (SOT-223). The primary difference is active product status and ROHS3 compliance versus the obsolete, non-compliant original part.

Q: What is the difference between 500mA and 1.5A rated LM317 variants?

A: Output current rating is the primary difference. The 500mA variants (LM317MSTT3, LM317MSTT3G, LM317MDCYR) are suitable for applications requiring up to 500mA. The 1.5A variants provide three times the current capability while maintaining identical voltage regulation characteristics and pin compatibility. Selection depends on application current requirements.

Q: Are all substitute parts pin-compatible?

A: Yes. All listed substitute parts use TO-261-4 or TO-261AA package designations with SOT-223 or SOT-223-4 supplier packages. Pin configuration is identical across all variants, enabling direct PCB replacement without layout modification.

Q: What is the significance of the minimum output voltage difference (1.2V versus 1.25V)?

A: The LM317MSTT3 and LM317DCYR (UMW) specify 1.2V minimum output voltage, while most Texas Instruments variants specify 1.25V. For applications requiring output voltages below 1.25V, the onsemi LM317MSTT3G or UMW LM317DCYR are required. For applications at or above 1.25V, all variants are functionally equivalent.

Q: Why do some parts have extended temperature range (-40°C to 125°C)?

A: Extended temperature range variants (LM317AEMP/NOPB, LM317AEMPX/NOPB, LM317MDCYR) are qualified for operation at lower ambient temperatures. Selection depends on application environment. Standard temperature range parts (0°C to 125°C) are suitable for typical industrial and commercial applications.

Q: What does ROHS3 compliance mean for this component?

A: ROHS3 compliance indicates the part meets Restriction of Hazardous Substances Directive requirements, restricting lead and other hazardous materials. The original LM317MSTT3 is non-compliant. All active substitute parts listed are ROHS3 compliant, meeting modern procurement and environmental standards.

Q: Which substitute offers the best inventory availability?

A: LM317AEMPX/NOPB from Texas Instruments has the highest inventory at 5,000,400 pieces. This part provides 1.5A output current with extended temperature range and ROHS3 compliance. For direct 500mA equivalents, LM317MSTT3G offers 40,300 pieces.

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