LP3984IMFX-1.8 Equivalent & Substitute Parts

Part Overview

The LP3984IMFX-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, which necessitates identification of active alternative components that maintain electrical and mechanical compatibility for new designs and production continuity.

Key Parameters

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

Substitute Part Grouping Explanation

Substitution eligibility is determined by the following mandatory parameters:

Output Voltage: Must be fixed at 1.8V
Output Current: Minimum 150mA (equal or greater capacity acceptable)
Package Type: SOT-23-5 or TSOT-23-5 (pin-compatible surface mount packages)
Input Voltage Range: Must accommodate 6V maximum input
Operating Temperature: Must support -40°C ~ 125°C range
Output Configuration: Positive fixed output, single regulator
Control Features: Enable function required

Substitute parts are grouped into two categories:

Category A - Direct Replacements (150mA Output Current): Parts with identical 150mA output current rating and SOT-23-5 packaging, suitable for direct PCB substitution without design modification.

Category B - Enhanced Alternatives (Higher Output Current): Parts with output current ratings exceeding 150mA in compatible packaging, providing design flexibility for applications requiring additional current margin or future scaling.

Parameter Comparison

Part Number	Manufacturer	Output Voltage	Output Current	Input Voltage (Max)	Dropout Voltage	Quiescent Current	Package	Operating Temp	Product Status
LP3984IMFX-1.8	Texas Instruments	1.8V	150mA	6V	0.12V @ 150mA	125 µA	SOT-23-5	-40°C ~ 125°C	Obsolete
ADP121-AUJZ18R7	Analog Devices Inc.	1.8V	150mA	5.5V	—	21 µA	TSOT-23-5	-40°C ~ 125°C	Active
ADP162AUJZ-1.8-R7	Analog Devices Inc.	1.8V	150mA	5.5V	—	1.25 µA	TSOT-23-5	-40°C ~ 125°C	Active
ADP165AUJZ-1.8-R7	Analog Devices Inc.	1.8V	150mA	5.5V	—	2.4 µA	TSOT-23-5	-40°C ~ 125°C	Active
ADP166AUJZ-1.8-R7	Analog Devices Inc.	1.8V	150mA	5.5V	—	2.4 µA	TSOT-23-5	-40°C ~ 125°C	Active
BU18SD2MG-MTR	Rohm Semiconductor	1.8V	200mA	6V	0.29V @ 100mA	80 µA	5-SSOP	-40°C ~ 105°C	Active
BU18UC3WG-TR	Rohm Semiconductor	1.8V	300mA	5.5V	0.32V @ 300mA	90 µA	5-SSOP	-40°C ~ 85°C	Not For New Designs
MCP1711T-18I/OT	Microchip Technology	1.8V	150mA	6V	1.4V @ 150mA	1.27 µA	SOT-23-5	-40°C ~ 85°C	Active
MIC5318-1.8YD5-TR	Microchip Technology	1.8V	300mA	6V	—	150 µA	TSOT-23-5	-40°C ~ 125°C	Active

Engineering Selection Recommendations

Primary Recommendation - Category A (Direct Replacement)

ADP162AUJZ-1.8-R7 and ADP165AUJZ-1.8-R7 from Analog Devices are the preferred direct substitutes. Both devices are active products with RoHS3 compliance, matching the 1.8V fixed output and 150mA current rating. These parts feature significantly lower quiescent current (1.25 µA and 2.4 µA respectively) compared to the original 125 µA, reducing standby power consumption. TSOT-23-5 packaging is pin-compatible with SOT-23-5 layouts. Both support the full -40°C ~ 125°C operating temperature range.

Secondary Recommendation - Category A (Direct Replacement)

ADP121-AUJZ18R7 from Analog Devices provides identical electrical specifications with 21 µA quiescent current and active product status. This part is suitable for applications where the lower quiescent current of ADP162/ADP165 is not required.

Alternative Recommendation - Category B (Enhanced Current Capacity)

MIC5318-1.8YD5-TR from Microchip Technology delivers 300mA output current in TSOT-23-5 packaging with active product status and RoHS3 compliance. This device maintains the full -40°C ~ 125°C temperature range and 6V maximum input voltage, making it suitable for designs requiring additional current margin beyond the original 150mA specification.

Not Recommended for New Designs

BU18UC3WG-TR is marked "Not For New Designs" and should be avoided for new product development despite meeting electrical parameters.

Frequently Asked Questions (FAQ)

Q: Can ADP162AUJZ-1.8-R7 be used as a direct replacement for LP3984IMFX-1.8?

A: Yes. Both devices deliver 1.8V fixed output at 150mA in pin-compatible SOT-23-5/TSOT-23-5 packages. The ADP162 is an active product with RoHS3 compliance and lower quiescent current, making it a superior direct replacement.

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

A: TSOT-23-5 is a thin variant of SOT-23-5 with identical pin configuration and PCB footprint. Both packages are mechanically and electrically interchangeable for this application.

Q: Why do some substitute parts have higher output current ratings?

A: Parts like MIC5318-1.8YD5-TR (300mA) and BU18SD2MG-MTR (200mA) provide additional current capacity beyond the original 150mA specification. These are suitable for applications requiring higher current delivery or designs with future scaling requirements.

Q: Are all recommended substitutes RoHS3 compliant?

A: Yes. All active substitute parts listed carry RoHS3 compliance certification, meeting current environmental and regulatory requirements.

Q: What is the significance of quiescent current differences?

A: Quiescent current determines standby power consumption. ADP162AUJZ-1.8-R7 (1.25 µA) and ADP165AUJZ-1.8-R7 (2.4 µA) consume significantly less standby power than the original LP3984IMFX-1.8 (125 µA), beneficial for battery-powered or low-power applications.

Q: Can MCP1711T-18I/OT be used as a substitute?

A: MCP1711T-18I/OT meets the 1.8V output and 150mA current requirements in SOT-23-5 packaging with active product status. However, its 1.4V dropout voltage at 150mA is substantially higher than the original 0.12V, which may impact performance in low-input-voltage applications. Operating temperature range is limited to -40°C ~ 85°C versus the original -40°C ~ 125°C.

Q: Why is BU18UC3WG-TR not recommended despite meeting specifications?

A: BU18UC3WG-TR carries a "Not For New Designs" product status designation, indicating the manufacturer has discontinued active support for new applications. This status typically precedes full obsolescence and should be avoided in new product development.

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