LP3984IMF-1.8 Equivalent & Substitute Parts

Part Overview

The LP3984IMF-1.8 is a linear voltage regulator IC from Texas Instruments designed to deliver a fixed 1.8V output at 150mA in a compact SOT-23-5 surface mount package. This device is classified as obsolete, making equivalent and substitute parts necessary for ongoing production and maintenance applications. The regulator features enable control, over-temperature protection, and short-circuit protection, with a maximum input voltage of 6V and a dropout voltage of 0.12V at full load.

Key Parameters

Parameter	Value
Output Voltage (Fixed)	1.8V
Output Current	150mA
Input Voltage (Max)	6V
Dropout Voltage (Max)	0.12V @ 150mA
Quiescent Current	125 µA
Operating Temperature Range	-40°C to 125°C
Package Type	SOT-23-5 (SC-74A)
Control Features	Enable
Protection Features	Over Temperature, Short Circuit

Substitute Part Grouping Explanation

Substitution for the LP3984IMF-1.8 is determined by the following critical parameters:

Fixed output voltage of 1.8V
Minimum output current capability of 150mA
Maximum input voltage of 6V or greater
SOT-23-5 package compatibility
Enable control feature
Operating temperature range of -40°C to 125°C (or compatible subset)
Surface mount technology

Substitute parts are grouped into two categories based on these criteria: direct functional equivalents with matching electrical specifications, and alternative regulators with enhanced performance characteristics that maintain backward compatibility within the specified parameter envelope.

Parameter Comparison

Part Number	Manufacturer	Output Voltage	Output Current	Input Voltage (Max)	Dropout Voltage (Max)	Quiescent Current	Operating Temp	Package	Product Status
LP3984IMF-1.8	Texas Instruments	1.8V	150mA	6V	0.12V @ 150mA	125 µA	-40°C to 125°C	SOT-23-5	Obsolete
LP3990MF-1.8/NOPB	National Semiconductor	1.8V	150mA	6V	0.2V @ 150mA	80 µA	-40°C to 85°C	SOT-23-5	Active
LP3990MFX-1.8/NOPB	Texas Instruments	1.8V	150mA	6V	0.2V @ 150mA	80 µA	-40°C to 85°C	SOT-23-5	Active
LD3985M18R	STMicroelectronics	1.8V	150mA	6V	Not specified	150 µA	-40°C to 125°C	SOT-23-5	Active
ADP121-AUJZ18R7	Analog Devices Inc.	1.8V	150mA	5.5V	Not specified	21 µA	-40°C to 125°C	TSOT-23-5	Active
ADP162AUJZ-1.8-R7	Analog Devices Inc.	1.8V	150mA	5.5V	Not specified	1.25 µA	-40°C to 125°C	TSOT-23-5	Active
ADP165AUJZ-1.8-R7	Analog Devices Inc.	1.8V	150mA	5.5V	Not specified	2.4 µA	-40°C to 125°C	TSOT-23-5	Active
ADP166AUJZ-1.8-R7	Analog Devices Inc.	1.8V	150mA	5.5V	Not specified	2.4 µA	-40°C to 125°C	TSOT-23-5	Active
BU18SD2MG-MTR	Rohm Semiconductor	1.8V	200mA	6V	0.29V @ 100mA	80 µA	-40°C to 105°C	5-SSOP	Active
BU18UC3WG-TR	Rohm Semiconductor	1.8V	300mA	5.5V	0.32V @ 300mA	90 µA	-40°C to 85°C	5-SSOP	Not For New Designs

Engineering Selection Recommendations

Direct Functional Equivalents (Recommended for Replacement)

LP3990MFX-1.8/NOPB from Texas Instruments is the primary recommended substitute. It maintains the same 1.8V output, 150mA current rating, and 6V maximum input voltage in an identical SOT-23-5 package. The part is active and RoHS3 compliant. The dropout voltage increases from 0.12V to 0.2V, and the operating temperature range narrows to -40°C to 85°C; these differences are acceptable for most applications within the original design envelope.

LD3985M18R from STMicroelectronics provides an alternative with identical electrical specifications and extended temperature range matching the original (-40°C to 125°C). This part is active and RoHS3 compliant, making it suitable for applications requiring the full temperature range.

Enhanced Performance Alternatives

The Analog Devices ADP162AUJZ-1.8-R7 and ADP165AUJZ-1.8-R7 offer significantly lower quiescent current (1.25 µA and 2.4 µA respectively) compared to the original 125 µA, beneficial for battery-powered applications. Both are active, RoHS3 compliant, and support the full -40°C to 125°C temperature range. The package transitions to TSOT-23-5 (thin variant), which is mechanically compatible with SOT-23-5 footprints. Maximum input voltage is 5.5V, which is acceptable for most 6V-input designs with appropriate margin.

Higher Current Alternatives

BU18SD2MG-MTR from Rohm Semiconductor provides 200mA output current in a 5-SSOP package with 6V maximum input voltage. This part is active and automotive-qualified (AEC-Q100), suitable for applications requiring higher current delivery.

Legacy Status Consideration

BU18UC3WG-TR is marked "Not For New Designs" and should be avoided for new product development, though it remains available for legacy system maintenance.

Frequently Asked Questions (FAQ)

Q: Can I use ADP165AUJZ-1.8-R7 as a direct replacement for LP3984IMF-1.8?

A: Yes, with package consideration. The ADP165AUJZ-1.8-R7 maintains the same 1.8V output and 150mA current rating. The package changes from SOT-23-5 to TSOT-23-5 (thin variant), which is mechanically compatible with existing SOT-23-5 PCB footprints. The maximum input voltage is 5.5V instead of 6V; verify your input supply does not exceed this limit. Quiescent current is significantly lower (2.4 µA vs. 125 µA), which is advantageous.

Q: What is the difference between SOT-23-5 and TSOT-23-5 packages?

A: TSOT-23-5 is a thin variant of SOT-23-5 with identical pin spacing and footprint compatibility. The primary difference is reduced package height, which may be beneficial for space-constrained designs. Both packages are surface mount and use the same land pattern.

Q: Why does LP3990MFX-1.8/NOPB have a higher dropout voltage than the original?

A: The LP3990MFX-1.8/NOPB has a dropout voltage of 0.2V at 150mA compared to 0.12V for the LP3984IMF-1.8. This 0.08V difference is within acceptable margins for most applications. Verify that your input supply voltage provides sufficient headroom above the 1.8V output requirement plus the dropout voltage.

Q: Can I use BU18SD2MG-MTR if my application only requires 150mA?

A: Yes. The BU18SD2MG-MTR is rated for 200mA output current, so it safely handles 150mA loads. The higher current rating provides design margin and does not negatively impact performance at lower currents. This part is automotive-qualified (AEC-Q100) and active, making it suitable for new designs.

Q: What is the impact of lower quiescent current in ADP162AUJZ-1.8-R7?

A: The ADP162AUJZ-1.8-R7 has a quiescent current of 1.25 µA compared to 125 µA in the original LP3984IMF-1.8. This 100x reduction is significant for battery-powered applications, reducing standby power consumption. For line-powered applications, the difference is negligible.

Q: Are all substitute parts RoHS compliant?

A: All recommended active substitutes (LP3990MFX-1.8/NOPB, LD3985M18R, ADP121-AUJZ18R7, ADP162AUJZ-1.8-R7, ADP165AUJZ-1.8-R7, ADP166AUJZ-1.8-R7, and BU18SD2MG-MTR) are RoHS3 compliant. The original LP3984IMF-1.8 is RoHS non-compliant due to its obsolete status.

Q: Which substitute offers the best thermal performance?

A: LD3985M18R from STMicroelectronics maintains the original operating temperature range of -40°C to 125°C and includes over-temperature protection. ADP162AUJZ-1.8-R7 and ADP165AUJZ-1.8-R7 also support the full -40°C to 125°C range. For applications requiring extended temperature operation, these three parts are preferred.

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