LP3855ET-3.3 Linear Voltage Regulator — Equivalent & Substitute Parts

Part Overview

The LP3855ET-3.3 is a linear voltage regulator IC from Texas Instruments, classified as a Power Management (PMIC) component. It delivers a fixed 3.3V output at 1.5A in a TO-220-5 package configuration. The device features integrated protection against overcurrent, overtemperature, and short-circuit conditions, with an enable control feature for power management applications.

The LP3855ET-3.3 is currently listed as obsolete. Identifying equivalent and substitute parts is necessary to maintain design continuity, ensure supply chain availability, and support ongoing production or maintenance of systems utilizing this regulator.

Key Parameters

Parameter	Value
Output Voltage (Fixed)	3.3V
Output Current	1.5A
Input Voltage (Max)	7V
Voltage Dropout (Max)	0.38V @ 1.5A
Quiescent Current (Iq)	3 mA
PSRR	73dB ~ 57dB (120Hz)
Protection Features	Over Current, Over Temperature, Short Circuit
Control Features	Enable
Operating Temperature Range	-40°C ~ 125°C
Package / Case	TO-220-5 Formed Leads
Mounting Type	Through Hole

Substitute Part Grouping Explanation

Substitute parts for the LP3855ET-3.3 are classified into three categories based on electrical and mechanical compatibility:

Direct Manufacturer Equivalent (Pin-Compatible, Same Electrical Characteristics)

LP3855ET-3.3/NOPB: Identical electrical specifications and package. Differs only in packaging format (Tube vs. unspecified original) and product status (Active vs. Obsolete). RoHS3 compliant.

Parametric Equivalents (Same Output Voltage, Current, Package, Minor Parameter Variations)

LP3852ET-3.3/NOPB (National Semiconductor)
LP3875ET-3.3/NOPB (Texas Instruments)
LP3962ET-3.3/NOPB (Texas Instruments)
LP3962ET-3.3/LB05 (Texas Instruments)
LP3965ET-3.3/NOPB (Texas Instruments)

These parts maintain the core electrical specifications: 3.3V fixed output, 1.5A output current, TO-220-5 package, and identical protection features. Variations exist in quiescent current (3–9 mA), voltage dropout (0.38–0.55V @ 1.5A), and supply current (10–15 mA). All are RoHS3 compliant and active or available products.

Manufacturer-Recommended Alternative (Enhanced Specifications)

LT1963AET-3.3#PBF (Analog Devices Inc.)
LT1963ET-3.3#PBF (Analog Devices Inc.)

These Analog Devices regulators provide the same 3.3V output and 1.5A current in TO-220-5 packages but feature higher maximum input voltage (20V vs. 7V), lower quiescent current (1.5 mA), and reverse polarity protection. These are suitable for applications requiring extended input voltage range or lower standby power consumption.

Parameter Comparison

Part Number	Manufacturer	Product Status	Output Voltage	Output Current	Input Voltage (Max)	Dropout @ 1.5A	Iq (mA)	Package	RoHS Status
LP3855ET-3.3	Texas Instruments	Obsolete	3.3V	1.5A	7V	0.38V	3	TO-220-5	Non-compliant
LP3855ET-3.3/NOPB	Texas Instruments	Active	3.3V	1.5A	7V	0.38V	3	TO-220-5	ROHS3 Compliant
LP3852ET-3.3/NOPB	National Semiconductor	Active	3.3V	1.5A	7V	0.38V	3	TO-220-5	ROHS3 Compliant
LP3875ET-3.3/NOPB	Texas Instruments	Active	3.3V	1.5A	7V	0.55V	5	TO-220-5	ROHS3 Compliant
LP3962ET-3.3/NOPB	Texas Instruments	Active	3.3V	1.5A	7V	0.55V	9	TO-220-5	ROHS3 Compliant
LP3962ET-3.3/LB05	Texas Instruments	Last Time Buy	3.3V	1.5A	7V	0.55V	9	TO-220-5	ROHS3 Compliant
LP3965ET-3.3/NOPB	Texas Instruments	Active	3.3V	1.5A	7V	0.55V	9	TO-220-5	ROHS3 Compliant
LT1963AET-3.3#PBF	Analog Devices Inc.	Active	3.3V	1.5A	20V	0.55V	1.5	TO-220-5	ROHS3 Compliant
LT1963ET-3.3#PBF	Analog Devices Inc.	Active	3.3V	1.5A	20V	0.55V	1.5	TO-220-5	ROHS3 Compliant

Engineering Selection Recommendations

For Direct Replacement (Identical Electrical Performance) Select LP3855ET-3.3/NOPB. This part maintains all electrical specifications of the original LP3855ET-3.3 while offering active product status and RoHS3 compliance. It is the preferred choice for designs requiring no circuit modifications.

For Parametric Substitution (Acceptable Performance Variations) LP3852ET-3.3/NOPB, LP3875ET-3.3/NOPB, LP3962ET-3.3/NOPB, LP3962ET-3.3/LB05, and LP3965ET-3.3/NOPB are suitable alternatives when the original part is unavailable. All maintain 3.3V output, 1.5A current capability, and TO-220-5 packaging. Designs tolerating increased voltage dropout (0.55V vs. 0.38V) and higher quiescent current (5–9 mA vs. 3 mA) can use these parts without circuit redesign. All are RoHS3 compliant and actively available or in Last Time Buy status.

For Enhanced Performance Requirements LT1963AET-3.3#PBF and LT1963ET-3.3#PBF from Analog Devices provide superior specifications: maximum input voltage of 20V (vs. 7V), lower quiescent current of 1.5 mA, and reverse polarity protection. These are recommended for applications requiring extended input voltage range or reduced standby power consumption. Both are RoHS3 compliant and actively available.

Compliance Considerations All recommended substitutes are RoHS3 compliant. The original LP3855ET-3.3 is RoHS non-compliant; migration to any substitute improves regulatory compliance for new production or maintenance activities.

Frequently Asked Questions (FAQ)

Q: Can LP3855ET-3.3/NOPB be used as a direct drop-in replacement for LP3855ET-3.3? A: Yes. LP3855ET-3.3/NOPB is electrically and mechanically identical to the original part. The only differences are packaging format (Tube) and product status (Active vs. Obsolete). No circuit modifications are required.

Q: What is the difference between LP3855ET-3.3 and LP3852ET-3.3/NOPB? A: Both deliver 3.3V at 1.5A in TO-220-5 packages with identical dropout voltage (0.38V @ 1.5A) and quiescent current (3 mA). The primary difference is manufacturer: LP3855 is from Texas Instruments, while LP3852 is from National Semiconductor. Both are functionally equivalent.

Q: Can I use LP3875ET-3.3/NOPB instead of LP3855ET-3.3? A: Yes, with design consideration. LP3875ET-3.3/NOPB provides the same 3.3V output and 1.5A current in an identical TO-220-5 package. However, it has higher voltage dropout (0.55V vs. 0.38V @ 1.5A) and higher quiescent current (5 mA vs. 3 mA). Verify that your application tolerates these parameter variations before substitution.

Q: Why would I choose LT1963AET-3.3#PBF over the LP series alternatives? A: The LT1963AET-3.3#PBF is suitable if your application requires input voltages up to 20V (vs. 7V maximum for LP series) or if lower standby power consumption is critical (1.5 mA quiescent current vs. 3–9 mA for LP series). It also includes reverse polarity protection, which the LP series lacks.

Q: Are all substitute parts RoHS compliant? A: Yes. All recommended substitutes are RoHS3 compliant. The original LP3855ET-3.3 is RoHS non-compliant, so any substitute improves regulatory compliance.

Q: What is the difference between LP3962ET-3.3/NOPB and LP3962ET-3.3/LB05? A: Both parts are electrically identical with 3.3V output, 1.5A current, and TO-220-5 packaging. The difference is product status: LP3962ET-3.3/NOPB is Active, while LP3962ET-3.3/LB05 is Last Time Buy. For new designs, select LP3962ET-3.3/NOPB to ensure long-term availability.

Q: Can I use these substitutes in applications with input voltages above 7V? A: No, unless you select LT1963AET-3.3#PBF or LT1963ET-3.3#PBF, which support input voltages up to 20V. All LP series regulators are rated for maximum input voltage of 7V. Exceeding this rating will damage the device.

Q: Do all substitute parts have the same protection features as the original? A: All LP series substitutes (LP3852, LP3875, LP3962, LP3965) include overcurrent, overtemperature, and short-circuit protection, matching the original LP3855ET-3.3. The LT1963 series adds reverse polarity protection in addition to these features.

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