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LM3940IMP-3.3 Linear Voltage Regulator Equivalent & Substitute Parts
Part Overview
The LM3940IMP-3.3 is a linear voltage regulator IC manufactured by Texas Instruments, designed to provide a fixed 3.3V output at 1A current capacity in a surface-mount SOT-223-4 package. This part is classified as obsolete, which necessitates identification of active equivalent and substitute components for new designs and ongoing production requirements. The device functions as a positive fixed output regulator with integrated over-temperature and short-circuit protection, suitable for applications requiring stable 3.3V power delivery from input sources up to 7.5V.
Substiute Parts
Key Parameters
| Parameter | Value |
|---|---|
| Output Voltage (Fixed) | 3.3V |
| Output Current | 1A |
| Maximum Input Voltage | 7.5V |
| Voltage Dropout (Max) | 0.2V @ 100mA |
| Output Configuration | Positive Fixed |
| Protection Features | Over Temperature, Short Circuit |
| Operating Temperature Range | -40°C ~ 125°C |
| Package Type | SOT-223-4 (TO-261-4, TO-261AA) |
| Mounting Type | Surface Mount |
| RoHS Status | ROHS3 Compliant |
| Moisture Sensitivity Level | 1 (Unlimited) |
Substitute Part Grouping Explanation
Substitution eligibility for the LM3940IMP-3.3 is determined by the following critical parameters:
Primary Substitution Criteria:
- Fixed output voltage of 3.3V
- Output current capability of 1A or greater
- Surface-mount SOT-223 package family (SOT-223-3 or SOT-223-4)
- Operating temperature range encompassing -40°C to 125°C
- Positive fixed output configuration
- Over-temperature and short-circuit protection
Secondary Compatibility Factors:
- Maximum input voltage rating of 6V or higher
- Voltage dropout specification suitable for application requirements
- RoHS3 compliance and MSL rating of 1 or 3
Substitute parts are grouped into two categories:
Category 1: Parametric Equivalents (Texas Instruments LM3940 Series) Parts LM3940IMP-3.3/NOPB and LM3940IMPX-3.3/NOPB maintain identical electrical specifications and package configuration to the main part, with active product status and higher inventory availability.
Category 2: Manufacturer-Recommended Alternatives Parts from Diodes Incorporated (AP2114HA-3.3TRG1, AP7361-33E-13, AP7365-33EG-13), Microchip Technology (MCP1824ST-3302E/DB, MIC37100-3.3WS, MIC37100-3.3WS-TR), onsemi (NCP1117ST33T3G), and MaxLinear (SPX3940AM3-L-3-3/TR) provide functional equivalence with variations in dropout voltage, quiescent current, and maximum input voltage ratings.
Parameter Comparison
| Part Number | Manufacturer | Status | Output Voltage | Output Current | Max Input Voltage | Dropout @ Load | Package | Temp Range | Protection |
|---|---|---|---|---|---|---|---|---|---|
| LM3940IMP-3.3 | Texas Instruments | Obsolete | 3.3V | 1A | 7.5V | 0.2V @ 100mA | SOT-223-4 | -40°C ~ 125°C | OT, SC |
| LM3940IMP-3.3/NOPB | Texas Instruments | Active | 3.3V | 1A | 7.5V | 0.2V @ 100mA | SOT-223-4 | -40°C ~ 125°C | OT, SC |
| LM3940IMPX-3.3/NOPB | Texas Instruments | Active | 3.3V | 1A | 7.5V | 0.2V @ 100mA | SOT-223-4 | -40°C ~ 125°C | OT, SC |
| AP2114HA-3.3TRG1 | Diodes Incorporated | Active | 3.3V | 1A | 6V | 0.75V @ 1A | SOT-223-3 | -40°C ~ 85°C | OC, OT |
| AP7361-33E-13 | Diodes Incorporated | Active | 3.3V | 1A | 6V | 0.7V @ 1A | SOT-223-3 | -40°C ~ 85°C | OC, OT, SC |
| AP7365-33EG-13 | Diodes Incorporated | Active | 3.3V | 600mA | 6V | 0.4V @ 600mA | SOT-223-3 | -40°C ~ 85°C | OC, OT |
| MCP1824ST-3302E/DB | Microchip Technology | Active | 3.3V | 300mA | 6V | 0.32V @ 300mA | SOT-223-3 | -40°C ~ 125°C | OT, SC, UVLO |
| MIC37100-3.3WS | Microchip Technology | Active | 3.3V | 1A | 6V | 0.5V @ 1A | SOT-223-3 | -40°C ~ 125°C | OC, OT |
| MIC37100-3.3WS-TR | Microchip Technology | Active | 3.3V | 1A | 6V | 0.5V @ 1A | SOT-223-3 | -40°C ~ 125°C | OC, OT |
| NCP1117ST33T3G | onsemi | Active | 3.3V | 1A | 20V | 1.2V @ 800mA | SOT-223 | 0°C ~ 125°C | OC, OT |
| SPX3940AM3-L-3-3/TR | MaxLinear, Inc. | Active | 3.3V | 1A | 16V | 0.55V @ 1A | SOT-223-3 | -40°C ~ 125°C | OC, OT, RP, SC, TV |
Legend: OT = Over Temperature, SC = Short Circuit, OC = Over Current, UVLO = Under Voltage Lockout, RP = Reverse Polarity, TV = Transient Voltage
Engineering Selection Recommendations
Direct Replacement (Highest Compatibility): LM3940IMP-3.3/NOPB and LM3940IMPX-3.3/NOPB are direct parametric equivalents from Texas Instruments with active product status. Both maintain identical electrical specifications, package configuration, and operating temperature range. These parts are recommended for applications where the original LM3940IMP-3.3 specifications must be preserved without modification.
Full-Current Alternatives (1A Output): MIC37100-3.3WS-TR (Microchip Technology) and SPX3940AM3-L-3-3/TR (MaxLinear) provide 1A output current with active status and RoHS3 compliance. MIC37100-3.3WS-TR operates across the full -40°C to 125°C temperature range with 0.5V dropout at 1A. SPX3940AM3-L-3-3/TR offers enhanced protection features including reverse polarity and transient voltage protection, with 0.55V dropout at 1A and extended input voltage rating to 16V.
Reduced-Current Alternatives: AP7365-33EG-13 (Diodes Incorporated) and MCP1824ST-3302E/DB (Microchip Technology) provide reduced output current ratings of 600mA and 300mA respectively. These parts are suitable only for applications where load current does not exceed their specified maximums. AP7365-33EG-13 offers superior dropout performance at 0.4V @ 600mA. MCP1824ST-3302E/DB includes under-voltage lockout protection and operates across -40°C to 125°C.
Extended Input Voltage Applications: NCP1117ST33T3G (onsemi) accepts input voltages up to 20V, compared to the main part's 7.5V maximum. This part is suitable for applications requiring higher input voltage tolerance, though it exhibits higher dropout voltage (1.2V @ 800mA) and operates only from 0°C to 125°C.
Compliance Verification: All substitute parts maintain RoHS3 compliance and MSL ratings of 1 or 3. Parts with MSL-3 rating (MIC37100 series) require controlled moisture exposure during storage and handling per IPC-A-610 standards.
Frequently Asked Questions (FAQ)
Q: Can LM3940IMP-3.3/NOPB be used as a direct replacement for the obsolete LM3940IMP-3.3?
A: Yes. LM3940IMP-3.3/NOPB is a parametric equivalent with identical electrical specifications, package configuration (SOT-223-4), and operating temperature range (-40°C to 125°C). The primary difference is active product status and higher inventory availability. No circuit modifications are required.
Q: What is the difference between SOT-223-3 and SOT-223-4 packages?
A: SOT-223-4 includes four pins (IN, GND, OUT, NC), while SOT-223-3 uses three pins (IN, GND, OUT). Both packages are mechanically compatible with TO-261-4 and TO-261AA footprints. The fourth pin in SOT-223-4 is typically not connected (NC) and does not affect circuit operation.
Q: Why do some substitute parts have lower output current ratings?
A: AP7365-33EG-13 (600mA) and MCP1824ST-3302E/DB (300mA) are designed for lower-power applications. These parts are suitable only if application load current does not exceed their specified maximums. Exceeding rated output current will trigger over-current protection.
Q: Which substitute part has the lowest dropout voltage?
A: AP7365-33EG-13 exhibits the lowest dropout voltage at 0.4V @ 600mA. For 1A applications, MIC37100-3.3WS-TR provides 0.5V dropout, and SPX3940AM3-L-3-3/TR provides 0.55V dropout.
Q: Can NCP1117ST33T3G be used in applications with input voltages above 7.5V?
A: Yes. NCP1117ST33T3G accepts input voltages up to 20V, making it suitable for higher input voltage applications. However, this part exhibits higher dropout voltage (1.2V @ 800mA) and operates only from 0°C to 125°C, compared to the main part's -40°C to 125°C range.
Q: What is the significance of MSL-3 rating on MIC37100 parts?
A: MSL-3 (Moisture Sensitivity Level 3) indicates the component requires controlled moisture exposure for 168 hours maximum after packaging opening. Parts must be stored in dry conditions and reflowed within the specified timeframe. MSL-1 parts (LM3940 series, AP7361, NCP1117) have unlimited shelf life without moisture control.
Q: Are all substitute parts RoHS3 compliant?
A: Yes. All listed substitute parts maintain RoHS3 compliance. The main part LM3940IMP-3.3 is also RoHS3 compliant, ensuring environmental and regulatory consistency across all alternatives.
Q: Which substitute part provides the most comprehensive protection features?
A: SPX3940AM3-L-3-3/TR includes over-current, over-temperature, reverse polarity, short-circuit, and transient voltage protection. This comprehensive protection set exceeds the main part's over-temperature and short-circuit protection.
Q: Can substitute parts with lower maximum input voltage ratings be used in applications designed for 7.5V input?
A: Parts with 6V maximum input rating (AP2114HA-3.3TRG1, AP7361-33E-13, AP7365-33EG-13, MIC37100 series) cannot be used in applications where input voltage may reach 7.5V. These parts will enter dropout or shutdown at voltages above 6V. Verify actual application input voltage before selection.
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