Texas Instruments LM3550SP/NOPB

Overview

LM3550SP/NOPB from Texas Instruments is a 5-A switched-capacitor super-capacitor flash LED driver with integrated NFET controller, I²C-programmable flash/torch currents (60–200 mA), selectable charge voltages (4.5 V/5 V/5.3 V), and ambient light/temperature sensing via ALD/TEMP pin. It operates from 2.7 V to 5.5 V input and drives high-power camera flash LEDs in mobile imaging systems.

For engineers reviewing the LM3550SP/NOPB datasheet, LM3550SP/NOPB pinout, LM3550SP/NOPB application, or LM3550SP/NOPB equivalent, this page delivers verified technical context, real-world timing behavior, thermal performance under flash load, I²C register mapping implications, and validated alternative drivers for super-capacitor-based flash architectures.

Technical Context

The LM3550SP/NOPB implements a multi-gain (1×/1.5×/2×) switched-capacitor charge pump with adaptive gain switching to maintain constant current during super-capacitor charging up to 5.3 V. Its external NFET controller regulates flash current independently of VOUT droop, enabling stable 5-A peak output despite capacitor voltage decay.

It integrates dual-function ALD/TEMP sensing with three-zone comparator thresholds (configurable via registers) for automatic flash-current scaling based on ambient light or NTC thermistor input, plus open-drain EOC signaling at 95% of target voltage and edge- or level-sensitive STROBE triggering with internal timeout protection.

Key Specifications

Pinout & Package

LM3550SP/NOPB uses a 16-pin UQFN package (3.0 mm × 2.5 mm × 0.8 mm) with exposed die-attach pad (DAP) connected to GND for thermal management.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar super-capacitor flash LED driver applications.

Compared with LM3550SP/NOPB, LM3554TP/NOPB trades peak flash current for integration density, while RT8546GQW sacrifices capacitor-based efficiency and thermal intelligence for broader input voltage support and simpler analog control.

Availability

LM3550SP/NOPB is available at Aetrix Electronics and suitable for digital camera modules, emergency lighting systems, barcode scanners, and handheld data terminals requiring stable component supply and long-term production continuity.

Supply support for LM3550SP/NOPB includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor leader delivering analog and embedded processing solutions, with deep expertise in power management and precision analog ICs.

The LM3550SP/NOPB belongs to TI's mobile flash LED driver product line, engineered specifically for super-capacitor–based high-current flash systems in space- and thermal-constrained portable imaging devices.

FAQ

What is the maximum super-capacitor charge voltage supported by the LM3550SP/NOPB?

The LM3550SP/NOPB supports four selectable super-capacitor charge voltages: 4.5 V, 5.0 V, 5.3 V, and an optimized setting. The 5.3-V option matches common 5.5-V-rated super-capacitors, ensuring safe operation with margin. This selection is made via I²C register configuration and directly determines the VOUT regulation point during charging. The LM3550SP/NOPB maintains tight regulation (±1.5% typical) across temperature and load conditions.

How does the ALD/TEMP pin function in ambient light sensing mode for the LM3550SP/NOPB?

In ambient light sensing mode, the ALD/TEMP pin accepts current from a reverse-biased photodiode or photoresistor network. The LM3550SP/NOPB compares this signal against internal 1-V reference thresholds to place the system in one of three ALS zones. Zone 0 permits full 5-A flash; Zone 1 limits flash to 70%; Zone 2 disables flash entirely. Thresholds are programmable via ALD/TEMP Sense High/Low Registers, and filtering is enhanced by adding a 1-µF capacitor from ALD/TEMP to GND.

Can the LM3550SP/NOPB drive multiple LEDs simultaneously, and what is required for that configuration?

Yes, the LM3550SP/NOPB can drive multiple LEDs by connecting their anodes to VOUT and cathodes to LED− (for torch mode) or to the drain of an external NFET controlled by FET_CON (for flash mode). For multi-LED flash, a single high-current NFET handles all parallel strings, while torch current remains regulated through the internal sink. Layout must minimize trace inductance on VOUT and LED− paths, and thermal design must accommodate total power dissipation - especially critical when driving >3 A aggregate flash current.

What is the purpose of the BAL pin on the LM3550SP/NOPB, and when is it required?

The BAL pin on the LM3550SP/NOPB provides active voltage balancing for two-series super-capacitor configurations. It regulates the midpoint voltage to exactly VOUT/2, preventing overvoltage on either cell - a critical safeguard since super-capacitors have low overvoltage tolerance. BAL is required whenever a 2-cell series stack is used to achieve higher working voltage (e.g., 5.3 V from two 2.7-V cells). If a single super-capacitor is used, the BAL pin is left unconnected.

Does the LM3550SP/NOPB include built-in protection features, and which ones are implemented?

Yes, the LM3550SP/NOPB integrates multiple hardware protections: output overvoltage protection (OVP) triggers at 5.479 V with 0.2-V hysteresis; thermal shutdown engages at 145°C (typical) and releases at 125°C; flash timeout disables current if STROBE remains asserted beyond programmed duration; and true shutdown disconnects the LED path to limit quiescent current to 4 µA. All protections operate autonomously without firmware intervention.