Analog Devices Inc. LT3475EFE-1#TRPBF

Overview

LT3475EFE-1#TRPBF 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. It delivers up to 1.5A per channel with ±3% LED current accuracy from 50mA to 1.5A, supports 4V–36V input, and enables grounded-cathode LED operation via high-side current sensing. It is used in automotive lighting systems requiring precise dimming and thermal robustness.

For engineers reviewing the LT3475EFE-1#TRPBF datasheet, LT3475EFE-1#TRPBF pinout, LT3475EFE-1#TRPBF application, or LT3475EFE-1#TRPBF equivalent, key selection criteria include its 200kHz–2MHz programmable switching frequency, 3000:1 true-color PWM dimming capability, open-LED protection (LT3475 only), and 25V maximum LED string voltage rating specific to the -1 variant.

Technical Context

The LT3475EFE-1#TRPBF implements a current-mode PWM architecture with dual independent control loops, each featuring an internal error amplifier (VC1/VC2), adjustable oscillator (RT pin), and high-side current sense for grounded-cathode topology. Its master-slave oscillator configuration enables anti-phase switching to reduce input ripple.

It integrates bipolar NPN power switches with 350mV typical V_CE(SAT) at 1.5A, uses external boost capacitors for gate drive enhancement, and includes frequency foldback during overload and thermal shutdown. The -1 suffix denotes extended 25V LED output voltage rating versus 15V for the base LT3475.

Key Specifications

Pinout & Package

LT3475EFE-1#TRPBF is housed in a 20-lead plastic TSSOP package with exposed thermal pad (Pin 21), which must be soldered to PCB ground for electrical integrity and thermal performance. Pin pitch is 0.65mm; body dimensions are 6.5mm × 4.4mm × 1.1mm.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC3783EFE#TRPBF and MAX16820ATP+T, the LT3475EFE-1#TRPBF offers lower system cost through integrated bipolar switches and reduced external component count, while delivering superior dimming fidelity and input ripple suppression-but with fixed buck topology and lower max input voltage.

Availability

LT3475EFE-1#TRPBF is available at Aetrix Electronics and suitable for automotive lighting, industrial display backlighting, and avionic cabin lighting requiring stable component supply, long-term lifecycle assurance, and traceable sourcing.

Supply support for LT3475EFE-1#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, Inc. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and power management semiconductors.

The LT3475/LT3475-1 product line was designed specifically for high-reliability, high-current LED lighting applications demanding precision current regulation, wide dimming range, and robust thermal performance in space-constrained environments.

FAQ

What is the maximum LED string voltage supported by the LT3475EFE-1#TRPBF?

The LT3475EFE-1#TRPBF supports up to 25V on its LED1 and LED2 pins, as specified in the Absolute Maximum Ratings table. This distinguishes it from the base LT3475 (15V max) and enables driving longer LED strings-such as three 3.4V white LEDs in series-without external voltage clamping. Exceeding 25V risks permanent damage to the output stage.

How does the LT3475EFE-1#TRPBF achieve 3000:1 true-color PWM dimming?

The LT3475EFE-1#TRPBF achieves 3000:1 true-color PWM dimming by disconnecting the VC error amplifier from the control loop during PWM low periods-preserving the exact current waveform shape when active. This avoids the current ramp-up/ramp-down artifacts that cause chromaticity shift in conventional dimming methods. The LT3475EFE-1#TRPBF's internal architecture ensures LED current remains constant and repeatable across the full dimming range.

Does the LT3475EFE-1#TRPBF include open-LED protection?

No-the LT3475EFE-1#TRPBF does not include internal open-LED protection. Unlike the LT3475 (which clamps LED pin voltage at 14V during open-circuit conditions), the LT3475-1 variant omits this feature. If open-LED fault detection is required, external circuitry-such as a voltage monitor on the LED pin with comparator and latch-must be added to prevent overvoltage stress on the BOOST pin when VIN exceeds 25V.

What is the purpose of the exposed thermal pad (Pin 21) on the LT3475EFE-1#TRPBF?

The exposed thermal pad (Pin 21) on the LT3475EFE-1#TRPBF serves dual functions: it provides a low-impedance electrical connection to ground and acts as the primary thermal path from the die to the PCB. Per the datasheet, it must be soldered to a solid ground plane with multiple thermal vias. Failure to connect Pin 21 results in excessive junction temperature rise, potential thermal shutdown, and degraded current regulation accuracy in the LT3475EFE-1#TRPBF.

Can the LT3475EFE-1#TRPBF operate with a single 12V input supplying both channels?

Yes-the LT3475EFE-1#TRPBF is fully rated for 4V–36V input and supports simultaneous operation of both channels from a common 12V rail. Its dual VIN pins (5 and 6) are internally tied and designed to handle combined input current up to ~3.5A. Layout best practice recommends symmetric routing and local 4.7μF ceramic bypassing at each VIN pin to maintain stability and minimize noise coupling between channels.