LM3940IMPX-3.3 Linear Voltage Regulator IC Equivalent & Substitute Parts

Part Overview

The LM3940IMPX-3.3 is a linear voltage regulator IC manufactured by Texas Instruments, designed to provide a fixed 3.3V output at 1A maximum current. This positive fixed output regulator operates across an input voltage range up to 7.5V with a maximum dropout voltage of 0.2V at 100mA. The device includes over-temperature and short-circuit protection, making it suitable for general-purpose power management applications in embedded systems and consumer electronics.

The main part number LM3940IMPX-3.3 is currently in Last Time Buy status, indicating end-of-life production. Identifying equivalent and substitute parts ensures design continuity and supply chain reliability for applications currently using this component.

Key Parameters

Parameter	Value
Output Voltage (Fixed)	3.3V
Output Current	1A
Input Voltage (Max)	7.5V
Dropout Voltage (Max)	0.2V @ 100mA
Operating Temperature Range	-40°C ~ 125°C
Package Type	SOT-223-4
Protection Features	Over Temperature, Short Circuit
RoHS Status	ROHS3 Compliant
Moisture Sensitivity Level	1 (Unlimited)

Substitute Part Grouping Explanation

Substitute parts for the LM3940IMPX-3.3 are classified into three categories based on substitution compatibility:

Direct Manufacturer Equivalents maintain identical electrical specifications and packaging, differing only in product status or packaging format. These parts are pin-compatible and require no circuit modifications.

Parametric Equivalents provide the same core electrical performance (3.3V output, 1A current capability, SOT-223 package) but may originate from different manufacturers or have minor variations in dropout voltage or quiescent current. These parts are functionally interchangeable in most applications.

Manufacturer-Recommended Alternatives offer similar functionality with variations in one or more key parameters. These parts may have different maximum input voltages, dropout voltages, output current ratings, or operating temperature ranges. Selection depends on specific application requirements.

The critical parameters determining substitution eligibility are:

Output voltage: 3.3V fixed
Output current capability: minimum 1A
Package type: SOT-223 (TO-261-4 or TO-261AA)
Operating temperature range: -40°C ~ 125°C preferred
Protection features: Over-temperature and short-circuit protection

Parameter Comparison

Part Number	Manufacturer	Output Voltage	Output Current	Input Voltage (Max)	Dropout Voltage (Max)	Operating Temp	Package	Product Status
LM3940IMPX-3.3	Texas Instruments	3.3V	1A	7.5V	0.2V @ 100mA	-40°C ~ 125°C	SOT-223-4	Last Time Buy
LM3940IMPX-3.3/NOPB	Texas Instruments	3.3V	1A	7.5V	0.2V @ 100mA	-40°C ~ 125°C	SOT-223-4	Active
LM3940IMP-3.3	Texas Instruments	3.3V	1A	7.5V	0.2V @ 100mA	-40°C ~ 125°C	SOT-223-4	Obsolete
LM3940IMP-3.3/NOPB	Texas Instruments	3.3V	1A	7.5V	0.2V @ 100mA	-40°C ~ 125°C	SOT-223-4	Active
AP2114HA-3.3TRG1	Diodes Incorporated	3.3V	1A	6V	0.75V @ 1A	-40°C ~ 85°C	SOT-223-3	Active
AP7361-33E-13	Diodes Incorporated	3.3V	1A	6V	0.7V @ 1A	-40°C ~ 85°C	SOT-223-3	Active
AP7365-33EG-13	Diodes Incorporated	3.3V	600mA	6V	0.4V @ 600mA	-40°C ~ 85°C	SOT-223-3	Active
MCP1824ST-3302E/DB	Microchip Technology	3.3V	300mA	6V	0.32V @ 300mA	-40°C ~ 125°C	SOT-223-3	Active
MIC37100-3.3WS	Microchip Technology	3.3V	1A	6V	0.5V @ 1A	-40°C ~ 125°C	SOT-223-3	Active
MIC37100-3.3WS-TR	Microchip Technology	3.3V	1A	6V	0.5V @ 1A	-40°C ~ 125°C	SOT-223-3	Active
SPX3940AM3-L-3-3/TR	MaxLinear, Inc.	3.3V	1A	16V	0.55V @ 1A	-40°C ~ 125°C	SOT-223-3	Active

Engineering Selection Recommendations

Direct Replacement (No Circuit Modification Required):

LM3940IMPX-3.3/NOPB and LM3940IMP-3.3/NOPB are the primary alternatives. Both maintain identical electrical specifications and SOT-223-4 packaging. LM3940IMPX-3.3/NOPB is recommended as the first choice due to Active product status and highest inventory availability (47,100 units). LM3940IMP-3.3 is Obsolete and should be avoided for new designs despite parametric equivalence.

Active Alternatives with Full 1A Output:

MIC37100-3.3WS and MIC37100-3.3WS-TR (Microchip Technology) provide 1A output capability with identical operating temperature range (-40°C ~ 125°C) and ROHS3 compliance. These parts feature SOT-223-3 packaging and are available in both tube and tape-and-reel formats. The primary trade-off is increased dropout voltage (0.5V @ 1A versus 0.2V @ 100mA on the original part).

SPX3940AM3-L-3-3/TR (MaxLinear, Inc.) offers 1A output with extended maximum input voltage (16V versus 7.5V), providing greater input voltage margin. This part is suitable for applications requiring higher input voltage tolerance.

Reduced Output Current Alternatives:

AP7365-33EG-13 (Diodes Incorporated) provides 600mA output with superior dropout voltage performance (0.4V @ 600mA). This part is appropriate only for applications with maximum current requirements below 600mA.

MCP1824ST-3302E/DB (Microchip Technology) provides 300mA output and is suitable only for low-current applications.

Not Recommended:

AP2114HA-3.3TRG1 and AP7361-33E-13 have reduced maximum operating temperature (85°C versus 125°C), limiting suitability for industrial temperature range applications.

Frequently Asked Questions (FAQ)

Q: Can I use LM3940IMP-3.3 as a direct replacement for LM3940IMPX-3.3?

A: LM3940IMP-3.3 is parametrically equivalent but is Obsolete. Use LM3940IMP-3.3/NOPB (Active status) instead for new designs and long-term supply assurance.

Q: What is the difference between SOT-223-4 and SOT-223-3 packaging?

A: SOT-223-4 includes four pins (input, output, ground, and an additional pin), while SOT-223-3 uses three pins (input, output, ground). Both are mechanically compatible in TO-261-4 and TO-261AA footprints, but verify PCB layout compatibility before substitution.

Q: Can I use MIC37100-3.3WS-TR instead of LM3940IMPX-3.3?

A: Yes. MIC37100-3.3WS-TR provides identical 1A output at 3.3V with the same operating temperature range and ROHS3 compliance. The increased dropout voltage (0.5V @ 1A) may affect power dissipation in high-current applications but is acceptable for most general-purpose designs.

Q: Why does SPX3940AM3-L-3-3/TR have a higher maximum input voltage?

A: SPX3940AM3-L-3-3/TR is designed for applications requiring higher input voltage tolerance (16V maximum). This extended rating provides additional design margin but does not affect output voltage or current specifications.

Q: Is MCP1824ST-3302E/DB suitable for my 1A application?

A: No. MCP1824ST-3302E/DB is rated for 300mA maximum output current. Use this part only if your application requires 300mA or less. For 1A applications, select MIC37100-3.3WS-TR, LM3940IMP-3.3/NOPB, or SPX3940AM3-L-3-3/TR.

Q: Are all substitute parts ROHS3 compliant?

A: All listed substitute parts are ROHS3 compliant except SPX3940AM3-L-3-3/TR, which is RoHS Compliant (standard RoHS, not ROHS3). Verify compliance requirements for your application before selection.

Q: What is the impact of dropout voltage differences on my circuit?

A: Dropout voltage determines the minimum input voltage required to maintain regulated output. The original part (0.2V @ 100mA) requires lower input voltage than alternatives with higher dropout ratings (0.5V ~ 0.75V). In low-input-voltage applications, the original part or LM3940IMP-3.3/NOPB are preferred.

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