Analog Devices Inc. LT3475IFE-1#PBF

Overview

LT3475IFE-1#PBF from Analog Devices (formerly Linear Technology) is a dual-channel, constant-current step-down DC/DC LED driver IC with integrated bipolar NPN power switches, designed for high-brightness LED lighting systems requiring precise 1.5A per channel current regulation, 3000:1 PWM dimming, and grounded-cathode LED configuration. It operates from 4V to 36V input, delivers up to 25V LED string voltage per channel, and supports anti-phase switching to reduce input ripple.

For engineers reviewing the LT3475IFE-1#PBF datasheet, LT3475IFE-1#PBF pinout, LT3475IFE-1#PBF application, or LT3475IFE-1#PBF equivalent, key selection criteria include its 20-lead TSSOP thermally enhanced package, –40°C to 125°C operating temperature grade, internal high-side current sense architecture, open-LED unprotected topology (LT3475-1 variant), and adjustable 200kHz–2MHz switching frequency via RT resistor.

Technical Context

The LT3475IFE-1#PBF implements a current-mode PWM control architecture with dual independent channels, each featuring cycle-by-cycle current limiting, frequency foldback during overload, and thermal shutdown. Its master-slave oscillator design enables anti-phase switching to minimize input capacitor RMS current.

Each channel uses an internal 0.067Ω current-sense resistor and a transconductance amplifier to servo the VC pin, achieving ±3% LED current accuracy from 50mA to 1.5A. The high-side sensing topology allows direct grounding of LED cathodes, simplifying thermal management in high-power lighting layouts.

Key Specifications

Pinout & Package

The LT3475IFE-1#PBF is housed in a 20-lead plastic TSSOP package with exposed thermal pad (Pin 21), requiring solder connection to PCB ground plane for thermal and electrical integrity.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual-channel constant-current LED driver applications.

Compared with LT3475EFE-1#PBF, the LT3475IFE-1#PBF adds 40°C higher maximum junction temperature tolerance and tighter parametric guarantees over full range; versus LM3409QMY/NOPB, it integrates dual switches and current sensing but sacrifices flexibility in voltage/current scaling and external FET selection.

Availability

LT3475IFE-1#PBF is available at Aetrix Electronics and suitable for automotive headlamp modules, avionic cockpit lighting, architectural accent lighting, and industrial machine vision illumination requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LT3475IFE-1#PBF 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, Inc. (ADI) is a global semiconductor leader specializing in high-performance analog, mixed-signal, and digital signal processing technologies, acquired Linear Technology in 2017 to expand its power management portfolio.

The LT3475IFE-1#PBF belongs to ADI's Linear LED Driver product line, engineered specifically for high-reliability, high-current, multi-string LED lighting in automotive, aerospace, and industrial applications demanding precision current regulation and robust thermal performance.

FAQ

What is the maximum LED string voltage supported by the LT3475IFE-1#PBF?

The LT3475IFE-1#PBF supports up to 25V per channel on its LED1 and LED2 pins, enabling driving of 6–8 standard white LEDs (3.4V–3.6V VF each) in series. This rating is specific to the LT3475-1 variant; the base LT3475 supports only 15V. Exceeding 25V risks damage to the internal current-sense circuitry and violates absolute maximum ratings.

Does the LT3475IFE-1#PBF include open-LED protection?

No, the LT3475IFE-1#PBF does not include internal open-LED protection. As the "-1" suffix indicates, this variant lacks the 14V clamp circuit present in the LT3475. If the LED string opens, the output voltage can rise to VIN + VF, potentially exceeding the 30V BOOST-to-SW rating. External overvoltage protection (e.g., Zener clamp or TVS) is required for robust operation.

How is the switching frequency set on the LT3475IFE-1#PBF?

The switching frequency of the LT3475IFE-1#PBF is set by a single resistor connected from the RT pin (Pin 14) to GND. A 24.3kΩ resistor yields 600kHz; values from 0.2kΩ to 100kΩ program frequencies from 2MHz down to 200kHz. The relationship is monotonic and documented in Table 1 of the datasheet - no calibration or trimming is needed.

Can the LT3475IFE-1#PBF drive LEDs with grounded cathodes?

Yes, the LT3475IFE-1#PBF uses high-side current sensing, which allows the LED cathodes to be directly connected to system ground. This simplifies thermal design (heat sinks attach to cathode side), avoids ground-loop issues in multi-channel systems, and eliminates the need for level-shifting circuitry - a key advantage over low-side sense LED drivers.

What is the purpose of the exposed pad (Pin 21) on the LT3475IFE-1#PBF package?

The exposed pad (Pin 21) on the LT3475IFE-1#PBF is electrically connected to GND and serves as the primary thermal conduction path from the die to the PCB. It must be soldered to a large copper ground plane with multiple thermal vias; failure to do so results in excessive junction temperature, premature thermal shutdown, and reduced reliability - especially at full 1.5A/channel load.