SPX3940AM3-L-3-3 Equivalent & Substitute Parts

Part Overview

The SPX3940AM3-L-3-3 is a linear voltage regulator IC from MaxLinear, Inc., designed to deliver a fixed 3.3V output at 1A in a surface-mount SOT-223-3 package. This device is classified as a Power Management PMIC and features integrated protection against overcurrent, overtemperature, reverse polarity, short circuit, and transient voltage conditions. The part is discontinued at DiGi Electronics, making equivalent substitutes necessary for ongoing design support and procurement.

Key Parameters

Parameter	Value
Output Voltage (Fixed)	3.3V
Output Current	1A
Input Voltage (Max)	16V
Dropout Voltage (Max)	0.55V @ 1A
Operating Temperature Range	-40°C to 125°C
Package Type	SOT-223-3
Mounting Type	Surface Mount
Protection Features	Over Current, Over Temperature, Reverse Polarity, Short Circuit, Transient Voltage
RoHS Status	RoHS Compliant

Substitute Part Grouping Explanation

Substitution eligibility is determined by the following criteria:

Primary Matching Parameters:

Fixed output voltage of 3.3V
Output current capability of 1A or greater
Maximum input voltage of 16V or higher
Operating temperature range of -40°C to 125°C
Surface-mount SOT-223 package (SOT-223-3 or SOT-223-4)
RoHS compliance

Acceptable Variations:

Dropout voltage may differ provided the application circuit tolerates the variation
Additional protection features beyond the original specification are acceptable
Higher output current ratings are acceptable for direct substitution
Enhanced control features (such as Enable pins) do not preclude substitution

Substitute parts are grouped into two categories based on output current capability: 1A-rated devices (direct 1:1 substitutes) and higher-current devices (1.5A rated, suitable for applications requiring additional headroom).

Parameter Comparison

Part Number	Manufacturer	Output Voltage	Output Current	Input Voltage (Max)	Dropout Voltage (Max)	Package	Product Status
SPX3940AM3-L-3-3	MaxLinear, Inc.	3.3V	1A	16V	0.55V @ 1A	SOT-223-3	Discontinued
LM3940IMP-3.3/NOPB	Texas Instruments	3.3V	1A	7.5V	0.2V @ 100mA	SOT-223-4	Active
LM3940IMPX-3.3/NOPB	Texas Instruments	3.3V	1A	7.5V	0.2V @ 100mA	SOT-223-4	Active
LT1963AEST-3.3#PBF	Analog Devices Inc.	3.3V	1.5A	20V	0.55V @ 1.5A	SOT-223-3	Active
LT1963AEST-3.3#TRPBF	Analog Devices Inc.	3.3V	1.5A	20V	0.55V @ 1.5A	SOT-223-3	Active
MCP1703-3302E/DB	Microchip Technology	3.3V	250mA	16V	0.725V @ 250mA	SOT-223-3	Active
MCP1703A-3302E/DB	Microchip Technology	3.3V	250mA	16V	0.725V @ 250mA	SOT-223-3	Active
MCP1703AT-3302E/DB	Microchip Technology	3.3V	250mA	16V	0.725V @ 250mA	SOT-223-3	Active
MCP1703T-3302E/DB	Microchip Technology	3.3V	250mA	16V	0.725V @ 250mA	SOT-223-3	Active

Engineering Selection Recommendations

Direct 1A Substitutes (Preferred for Pin-Compatible Replacement):

The LM3940IMP-3.3/NOPB and LM3940IMPX-3.3/NOPB from Texas Instruments are active, in-stock alternatives rated for 1A output current. Both devices are RoHS3 compliant and maintain the same fixed 3.3V output specification. The primary design consideration is the reduced maximum input voltage (7.5V versus 16V on the original part). These substitutes are suitable for applications where input voltage does not exceed 7.5V. The SOT-223-4 package is pin-compatible with SOT-223-3 in most circuit implementations.

Enhanced Current Capability Substitutes:

The LT1963AEST-3.3#PBF and LT1963AEST-3.3#TRPBF from Analog Devices Inc. provide 1.5A output current in SOT-223-3 packaging, offering increased current headroom. These devices support input voltages up to 20V and maintain the same dropout voltage characteristic (0.55V @ rated current). Both are RoHS3 compliant and active products. The packaging variant difference (tube versus cut tape) does not affect electrical compatibility.

Lower Current Alternatives (Application-Dependent):

The MCP1703 series from Microchip Technology (MCP1703-3302E/DB, MCP1703A-3302E/DB, MCP1703AT-3302E/DB, MCP1703T-3302E/DB) are rated for 250mA output current. These devices are suitable only for applications where load current does not exceed 250mA. All variants are RoHS3 compliant, active products with 16V maximum input voltage support. Selection among MCP1703 variants depends on packaging requirements (tube or cut tape) and temperature rating specifications.

Frequently Asked Questions (FAQ)

Q: Can the LM3940 series substitute for the SPX3940AM3-L-3-3 in all applications?

A: The LM3940IMP-3.3/NOPB and LM3940IMPX-3.3/NOPB are suitable substitutes provided the input voltage does not exceed 7.5V. If your circuit requires input voltages between 7.5V and 16V, the Analog Devices LT1963AEST series is the appropriate choice.

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

A: SOT-223-3 contains three pins (input, output, ground), while SOT-223-4 adds a fourth pin for enhanced thermal performance. Both packages are mechanically and electrically compatible in most applications, though PCB layout may require adjustment to accommodate the additional pin.

Q: Are the MCP1703 devices suitable direct replacements?

A: The MCP1703 series is suitable only for applications where output current does not exceed 250mA. If your design requires the full 1A capability of the original SPX3940AM3-L-3-3, use the LM3940 or LT1963AEST series instead.

Q: What is the significance of the dropout voltage difference between substitutes?

A: Dropout voltage determines the minimum input-to-output voltage differential required for proper regulation. The LM3940 series exhibits lower dropout voltage (0.2V @ 100mA) compared to the original part (0.55V @ 1A), which may improve efficiency in low-voltage input applications. The LT1963AEST maintains the same dropout voltage characteristic as the original part.

Q: Are all substitute parts RoHS compliant?

A: Yes. All listed substitute parts are RoHS3 compliant, meeting the same environmental standards as the original SPX3940AM3-L-3-3.

Q: Can I use a higher-current-rated device as a substitute?

A: Yes. Devices rated for higher output current (such as the 1.5A LT1963AEST series) are acceptable substitutes for applications originally designed for 1A output. The higher current rating provides additional design margin without affecting circuit operation.

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