LM3551SD LED Driver IC Equivalent & Substitute Parts

Part Overview

The LM3551SD is a Texas Instruments LED Driver IC designed for step-up (boost) DC-DC regulation with 1A flash output capability. This component is classified as obsolete, making substitute parts necessary for new designs and production continuity. The LM3551SD integrates an internal switch for efficient power conversion in camera flash and LED driver applications, operating across a 2.7V to 5.5V supply range with a switching frequency of 1.25MHz.

Key Parameters

Parameter	LM3551SD
Manufacturer	Texas Instruments
Category	Power Management (PMIC)
Type	DC DC Regulator
Topology	Step-Up (Boost)
Number of Outputs	1
Voltage - Supply (Min)	2.7V
Voltage - Supply (Max)	5.5V
Current - Output / Channel	1A (Flash)
Frequency	1.25MHz
Internal Switch(s)	Yes
Package / Case	14-WFDFN Exposed Pad
Mounting Type	Surface Mount
Operating Temperature	-40°C ~ 85°C (TA)
Product Status	Obsolete
RoHS Status	RoHS non-compliant

Substitute Part Grouping Explanation

Substitution for the LM3551SD is determined by the following critical parameters:

Topology: Step-Up (Boost) DC-DC regulation with internal switch
Supply Voltage Range: 2.7V to 5.5V input compatibility
Output Configuration: Single output channel
Current Capability: Minimum 1A output capacity
Switching Frequency: Operational range near 1.25MHz
Mounting: Surface mount packages compatible with PCB integration
Operating Temperature: -40°C to 85°C minimum range

Three active substitute parts meet these criteria: AP3602AKTR-G1 (Diodes Incorporated), IS31BL3508A-TTLS2-TR (Lumissil Microsystems), and MP3309AGQ-Z (Monolithic Power Systems Inc.). Each maintains the core boost topology and supply voltage specifications while offering different output current ratings, package options, and enhanced feature sets.

Parameter Comparison

Parameter	LM3551SD	AP3602AKTR-G1	IS31BL3508A-TTLS2-TR	MP3309AGQ-Z
Manufacturer	Texas Instruments	Diodes Incorporated	Lumissil Microsystems	Monolithic Power Systems Inc.
Type	DC DC Regulator	DC DC Regulator	DC DC Regulator	DC DC Regulator
Topology	Step-Up (Boost)	Step-Up (Boost)	Step-Up (Boost)	Step-Up (Boost)
Internal Switch(s)	Yes	Yes	Yes	Yes
Number of Outputs	1	1	1	1
Voltage - Supply (Min)	2.7V	2.7V	2.7V	2.7V
Voltage - Supply (Max)	5.5V	5V	5.5V	5.5V
Current - Output / Channel	1A (Flash)	100mA	1.6A (Switch)	Not specified
Frequency	1.25MHz	1.2MHz	1MHz	640kHz
Mounting Type	Surface Mount	Surface Mount	Surface Mount	Surface Mount
Package / Case	14-WFDFN Exposed Pad	SOT-23-6	SOT-23-6 Thin, TSOT-23-6	10-VFDFN Exposed Pad
Operating Temperature	-40°C ~ 85°C (TA)	-40°C ~ 85°C (TA)	-40°C ~ 85°C (TA)	-40°C ~ 125°C (TJ)
Product Status	Obsolete	Active	Active	Active
RoHS Status	RoHS non-compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

AP3602AKTR-G1 is suitable for applications requiring lower output current (100mA maximum). This part is ROHS3 compliant and active in production. The reduced current rating and SOT-23-6 package make it appropriate for space-constrained designs with lower power requirements. Maximum supply voltage is limited to 5V, which is within the LM3551SD range but represents a tighter specification.

IS31BL3508A-TTLS2-TR provides the highest output current capability (1.6A switch current) and supports both analog and PWM dimming functionality. This part maintains full 2.7V to 5.5V supply voltage compatibility and is ROHS3 compliant with active production status. The TSOT-23-6 package offers a compact form factor while delivering enhanced performance specifications.

MP3309AGQ-Z operates across the full 2.7V to 5.5V supply range and is ROHS3 compliant with active production status. This part features the widest operating temperature range (-40°C to 125°C junction temperature) and supports analog and PWM dimming. The 10-QFN package provides a different footprint option compared to the original 14-WFDFN, requiring PCB layout modification.

All three substitutes are active products with current RoHS3 compliance, addressing the obsolescence and compliance limitations of the LM3551SD.

Frequently Asked Questions (FAQ)

Q: Can AP3602AKTR-G1 directly replace LM3551SD in camera flash applications?

A: AP3602AKTR-G1 is limited to 100mA output current, while LM3551SD supports 1A flash current. This substitute is suitable only for applications requiring lower output current. For full 1A flash capability, IS31BL3508A-TTLS2-TR or MP3309AGQ-Z are more appropriate.

Q: What are the package differences between these substitutes?

A: LM3551SD uses 14-WFDFN (4x4mm) exposed pad packaging. AP3602AKTR-G1 and IS31BL3508A-TTLS2-TR use SOT-23-6 packages (smaller footprint). MP3309AGQ-Z uses 10-QFN (3x3mm) packaging. Each requires different PCB layout and land pattern designs.

Q: Are all substitutes RoHS compliant?

A: Yes. AP3602AKTR-G1, IS31BL3508A-TTLS2-TR, and MP3309AGQ-Z are all ROHS3 compliant, addressing the RoHS non-compliance of the obsolete LM3551SD.

Q: Which substitute has the best thermal performance?

A: MP3309AGQ-Z specifies the widest operating temperature range (-40°C to 125°C junction temperature) compared to the other substitutes and the original part (-40°C to 85°C ambient temperature).

Q: Can IS31BL3508A-TTLS2-TR support PWM dimming like the original?

A: IS31BL3508A-TTLS2-TR supports both analog and PWM dimming, providing enhanced dimming flexibility compared to the LM3551SD, which does not specify dimming capability.

Q: What is the supply voltage compatibility across all parts?

A: All substitutes support the 2.7V minimum supply voltage. AP3602AKTR-G1 is limited to 5V maximum, while IS31BL3508A-TTLS2-TR and MP3309AGQ-Z support the full 5.5V maximum range of the original LM3551SD.

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