LP3990MF-1.8 Linear Voltage Regulator — Equivalent & Substitute Parts

Part Overview

The LP3990MF-1.8 is a linear voltage regulator IC from Texas Instruments, classified as a positive fixed output 1.8V PMIC with 150mA output capacity in SOT-23-5 surface mount packaging. The device is marked as obsolete, making identification of functionally equivalent alternatives necessary for ongoing design support and component procurement. This reference provides engineering-grade substitute options based on strict parametric equivalence.

Key Parameters

Parameter	Value
Output Voltage (Fixed)	1.8V
Output Current	150mA
Input Voltage (Max)	6V
Dropout Voltage (Max)	0.2V @ 150mA
Quiescent Current	80 µA
PSRR	55dB ~ 35dB (1kHz ~ 10kHz)
Operating Temperature Range	-40°C ~ 85°C
Package / Case	SOT-23-5 (SC-74A, SOT-753)
Control Features	Enable
Protection Features	Over Temperature, Short Circuit
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution eligibility is determined by the following critical parameters:

Output Voltage: Must be fixed at 1.8V
Output Current Capacity: Minimum 150mA (equal or greater)
Input Voltage Range: Maximum 6V or higher
Package Type: SOT-23-5 or compatible 5-pin surface mount packages
Dropout Voltage: Lower or equal values preferred for thermal efficiency
Operating Temperature: Must support -40°C ~ 85°C minimum
Control Features: Enable function required
Protection: Over temperature and short circuit protection required

Substitute parts are grouped into two categories: Parametric Equivalents (direct replacements with identical electrical specifications) and Manufacturer Recommended Alternatives (functionally compatible with enhanced or modified specifications suitable for the same application space).

Parameter Comparison

Part Number	Manufacturer	Output Current	Dropout Voltage	Quiescent Current	PSRR (1kHz)	Package	Product Status	RoHS Compliance
LP3990MF-1.8	Texas Instruments	150mA	0.2V @ 150mA	80 µA	55dB	SOT-23-5	Obsolete	Non-compliant
LP3990MF-1.8/NOPB	National Semiconductor	150mA	0.2V @ 150mA	80 µA	55dB	SOT-23-5	Active	Not specified
LP3990MFX-1.8/NOPB	Texas Instruments	150mA	0.2V @ 150mA	80 µA	55dB	SOT-23-5	Active	ROHS3 Compliant
AP7335-18WG-7	Diodes Incorporated	300mA	0.3V @ 300mA	80 µA	65dB	SOT-25	Active	ROHS3 Compliant
AP7365-18WG-7	Diodes Incorporated	600mA	0.6V @ 600mA	80 µA	65dB	SOT-25	Active	ROHS3 Compliant
BU18SD2MG-MTR	Rohm Semiconductor	200mA	0.29V @ 100mA	80 µA	68dB	5-SSOP	Active	ROHS3 Compliant
BU18TD3WG-TR	Rohm Semiconductor	200mA	0.6V @ 200mA	60 µA	70dB	5-SSOP	Active	ROHS3 Compliant
BU18UC3WG-TR	Rohm Semiconductor	300mA	0.32V @ 300mA	90 µA	70dB	5-SSOP	Not For New Designs	ROHS3 Compliant
MIC5232-1.8YD5-TR	Microchip Technology	10mA	0.3V @ 10mA	3 µA	55dB	TSOT-23-5	Active	ROHS3 Compliant
MIC5256-1.8YM5-TR	Microchip Technology	150mA	0.25V @ 150mA	150 µA	60dB	SOT-23-5	Active	ROHS3 Compliant

Engineering Selection Recommendations

Direct Parametric Equivalents (Recommended for Immediate Substitution)

LP3990MFX-1.8/NOPB from Texas Instruments is the primary recommended substitute. It maintains identical electrical specifications (150mA output, 0.2V dropout, 80 µA quiescent current) and package format (SOT-23-5) while offering active product status and ROHS3 compliance. This part is suitable for direct board-level replacement without circuit modification.

LP3990MF-1.8/NOPB from National Semiconductor provides parametric equivalence with active product status, though RoHS compliance information is not specified in available documentation.

Enhanced Current Capacity Alternatives

For applications requiring higher output current capacity, the following parts provide increased current ratings while maintaining 1.8V fixed output and compatible package formats:

BU18SD2MG-MTR (Rohm Semiconductor, 200mA) offers improved dropout voltage performance (0.29V @ 100mA) and higher PSRR (68dB). This part qualifies as AEC-Q100 automotive grade and supports extended operating temperature to 105°C.

BU18TD3WG-TR (Rohm Semiconductor, 200mA) provides enhanced PSRR (70dB) and reduced quiescent current (60 µA) with active product status and ROHS3 compliance.

AP7335-18WG-7 (Diodes Incorporated, 300mA) and AP7365-18WG-7 (Diodes Incorporated, 600mA) deliver significantly higher current capacity with improved PSRR (65dB) in SOT-25 packaging. These parts are suitable for applications where increased headroom is beneficial.

Not Recommended for New Designs

BU18UC3WG-TR and BU18UB3WG-TR carry "Not For New Designs" status and should be avoided for new development projects, though they remain available for legacy system support.

Low-Current Specialized Alternative

MIC5232-1.8YD5-TR (Microchip Technology, 10mA) is suitable only for applications with significantly reduced current requirements and should not be used as a general substitute for the 150mA LP3990MF-1.8.

Frequently Asked Questions (FAQ)

Q: Can LP3990MFX-1.8/NOPB be used as a direct replacement for LP3990MF-1.8?

A: Yes. Both parts share identical electrical specifications (1.8V output, 150mA capacity, 0.2V dropout voltage, 80 µA quiescent current) and SOT-23-5 packaging. The primary difference is product status (active vs. obsolete) and RoHS compliance (ROHS3 vs. non-compliant). No circuit modifications are required.

Q: What is the difference between SOT-23-5 and 5-SSOP packaging?

A: Both are 5-pin surface mount packages with similar footprints and pin configurations. SOT-23-5 (also designated SC-74A or SOT-753) and 5-SSOP are mechanically and electrically compatible for this regulator class. PCB layout verification is recommended when switching between these package types.

Q: Can I use AP7335-18WG-7 (300mA) or AP7365-18WG-7 (600mA) if my circuit only requires 150mA?

A: Yes. Higher current-rated regulators are backward compatible with lower current requirements. The increased current capacity provides design margin and thermal headroom. However, verify that the different package format (SOT-25 vs. SOT-23-5) is compatible with your PCB layout.

Q: Why is MIC5256-1.8YM5-TR listed as a substitute if it has higher quiescent current (150 µA vs. 80 µA)?

A: MIC5256-1.8YM5-TR maintains the critical specifications for substitution: 1.8V fixed output, 150mA capacity, SOT-23-5 package, and -40°C to 125°C operating range. The elevated quiescent current (150 µA) represents a trade-off for enhanced protection features (UVLO) and improved PSRR performance (60dB). Selection depends on application power budget requirements.

Q: Are Rohm BU18 series parts suitable for automotive applications?

A: BU18SD2MG-MTR is explicitly qualified as AEC-Q100 automotive grade. Other BU18 variants (BU18TD3WG-TR, BU18UC3WG-TR, BU18UB3WG-TR) do not carry automotive qualification in the provided specifications and should be evaluated against specific automotive requirements before deployment.

Q: What is the significance of "Not For New Designs" status?

A: Parts marked "Not For New Designs" remain available for legacy system support and repair but should not be selected for new product development. These parts may have limited long-term availability or have been superseded by improved alternatives. For new designs, select parts with "Active" product status.

Q: Can I substitute MIC5232-1.8YD5-TR (10mA) for the LP3990MF-1.8 (150mA)?

A: No. MIC5232-1.8YD5-TR is rated for only 10mA output current and is unsuitable for applications requiring 150mA. This part is designed for low-power auxiliary supply applications and will not provide adequate current for standard LP3990MF-1.8 use cases.

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