Analog Devices Inc. LT3799IMSE#TRPBF

Overview

LT3799IMSE#TRPBF from Analog Devices (formerly Linear Technology) is an isolated flyback LED controller with active power factor correction, designed for TRIAC-dimmable offline LED drivers. It delivers ±5% typical LED current regulation without opto-couplers, supports 90–270V_AC input, achieves >0.97 typical PFC, and operates in critical conduction mode using a 16-lead MSOP package with exposed thermal pad.

For engineers reviewing the LT3799IMSE#TRPBF datasheet, LT3799IMSE#TRPBF pinout, LT3799IMSE#TRPBF application, or LT3799IMSE#TRPBF equivalent, key selection considerations include primary-side current sensing architecture, VIN_SENSE-based PFC implementation, CT-pin fault timing behavior, open/short LED protection via FB/CT coordination, and compatibility with high-voltage N-channel MOSFETs in isolated flyback topologies.

Technical Context

The LT3799IMSE#TRPBF implements a novel primary-side regulation scheme that calculates secondary LED current from primary peak current and DCM timing-eliminating opto-couplers. Its multiplier-based PFC loop modulates the current limit threshold proportionally to rectified line voltage sensed at VIN_SENSE, enabling >0.97 power factor across universal AC inputs.

Critical conduction mode operation is enforced via dv/dt detection on the transformer's third winding (DCM pin), triggering switch reactivation at valley points to minimize switching loss. The FAULT pin asserts low when FB exceeds 1.25V while CT > 1.25V, providing cycle-by-cycle open/short LED detection with automatic retry via CT capacitor discharge/recharge.

Key Specifications

Pinout & Package

LT3799IMSE#TRPBF is housed in a thermally enhanced 16-lead MSOP package (MSE) with exposed GND pad (Pin 17) requiring PCB soldering for thermal and electrical integrity. θ_JA = 50°C/W, θ_JC = 10°C/W.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar isolated PFC LED driver applications.

Compared with UCC28810DR and NCP1654ADR2G, the LT3799IMSE#TRPBF uniquely combines primary-side regulation, integrated 1.9A gate driver, and VIN_SENSE-based PFC in a single IC-enabling compact, high-PF, TRIAC-dimmable designs without opto-couplers or external drivers.

Availability

LT3799IMSE#TRPBF is available at Aetrix Electronics and suitable for street lighting, commercial downlights, industrial high-bay fixtures, UV-C disinfection modules, and TRIAC-dimmable architectural lighting requiring stable component supply and long-term obsolescence management.

Supply support for LT3799IMSE#TRPBF 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

Analog Devices acquired Linear Technology in 2017 and maintains full technical and manufacturing continuity for all Linear products, including precision analog and power management ICs.

The LT3799IMSE#TRPBF belongs to Linear's LED driver product line, engineered specifically for high-efficiency, isolated, TRIAC-dimmable LED lighting systems where opto-coupler elimination and primary-side regulation are critical design goals.

FAQ

What is the function of the CT pin on the LT3799IMSE#TRPBF?

The CT pin on the LT3799IMSE#TRPBF serves dual functions: during startup, it is charged with a 10 µA current until reaching 340 mV to initiate switching; during operation, it acts as a fault timer-charged to 1.25 V to enable regulation, and discharged at 200 nA upon fault detection (e.g., open LED) to implement automatic retry. The LT3799IMSE#TRPBF uses this pin to coordinate FAULT assertion and recovery without external timers.

How does the LT3799IMSE#TRPBF achieve power factor correction without an opto-coupler?

The LT3799IMSE#TRPBF achieves active PFC by scaling the current limit threshold using a multiplier circuit driven by the VIN_SENSE pin voltage, which reflects the rectified AC line waveform. This ensures input current follows the line voltage shape-yielding >0.97 typical PF-while primary-side regulation eliminates opto-coupler dependency. The LT3799IMSE#TRPBF performs this entirely on the primary side using internal analog computation.

Can the LT3799IMSE#TRPBF support both 120VAC and 220VAC inputs in the same design?

Yes, the LT3799IMSE#TRPBF supports universal input (90–270V_AC) through its VIN_SENSE pin interface and wide VIN operating range (23V turn-on, 12.3V turn-off). The device maintains >0.97 PF and ±5% LED current accuracy across both 120VAC and 220VAC when configured with appropriate transformer turns ratio and R_SENSE. The LT3799IMSE#TRPBF's critical conduction mode adapts frequency automatically to input voltage changes.

What protection features are built into the LT3799IMSE#TRPBF?

The LT3799IMSE#TRPBF integrates open LED and shorted LED protection via coordinated FB pin sampling and CT pin timing-asserting FAULT within milliseconds of fault occurrence. It also includes VIN overvoltage clamping (25V shunt), thermal shutdown (125°C junction limit), and current-limit hysteresis. These protections operate autonomously without microcontroller intervention. The LT3799IMSE#TRPBF implements hardware-level safety critical for Class I and II LED luminaires.

Is the LT3799IMSE#TRPBF compatible with leading-edge TRIAC dimmers?

Yes, the LT3799IMSE#TRPBF is explicitly designed for leading-edge TRIAC dimmer compatibility. It senses dimmer conduction angle via VIN_SENSE, maintains MOSFET conduction during TRIAC off-phase to prevent misfiring, and adjusts LED current in real time. The LT3799IMSE#TRPBF achieves smooth 1–100% dimming with minimal flicker and no audible noise across standard residential and commercial TRIAC dimmers.