Analog Devices Inc. LT3474IFE-1#PBF

Overview

LT3474IFE-1#PBF from Analog Devices (formerly Linear Technology) is a constant-frequency, current-mode step-down DC/DC converter optimized as a high-accuracy constant-current LED driver. It delivers up to 1 A output current with ±2% LED current accuracy over 35 mA–1 A range, supports 4V–36V input, and integrates boost diode and high-side current sense for grounded-cathode LED strings up to 26 V. It is used in automotive lighting and architectural LED systems requiring stable dimming.

For engineers reviewing the LT3474IFE-1#PBF datasheet, LT3474IFE-1#PBF pinout, LT3474IFE-1#PBF application, or LT3474IFE-1#PBF equivalent, key selection criteria include its 400:1 True Color PWM™ dimming ratio, thermal shutdown and frequency foldback protection, adjustable 200 kHz–2 MHz switching frequency via RT pin, and compatibility with ceramic output capacitors and small inductors in space-constrained designs.

Technical Context

The LT3474IFE-1#PBF employs current-mode PWM control with cycle-by-cycle current limiting and slope compensation, enabling fast transient response and stable operation across wide duty cycles. Its internal NPN bipolar power switch is driven by a BOOST pin voltage higher than VIN, generated via integrated Schottky diode and external capacitor.

It features high-side current sensing through dedicated OUT and LED pins, enabling grounded-cathode LED configurations. The VC pin serves as error amplifier output for loop compensation, while VADJ sets LED current via I_LED = 1 A × V_ADJ/1.25 V - supporting precise analog current programming independent of LED forward voltage.

Key Specifications

Pinout & Package

LT3474IFE-1#PBF uses a thermally enhanced 16-lead TSSOP package (FE) with exposed GND pad (Pin 17) that must be soldered to PCB for electrical and thermal integrity. Pins 1 and 16 are DNC (do not connect); all GND pins (8, 15, 17) must tie directly to ground plane.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC3783EFE#PBF and LM3409QMY/NOPB, LT3474IFE-1#PBF offers superior integration (integrated boost diode, high-side sense), tighter current accuracy (±2% vs. ±5%), and unique True Color PWM™ - making it optimal for space-constrained, color-stable LED systems operating within 4–36 V input and ≤26 V LED string limits.

Availability

LT3474IFE-1#PBF is available at Aetrix Electronics and suitable for automotive lighting, architectural LED systems, and industrial display backlighting requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LT3474IFE-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 acquired Linear Technology in 2017 and maintains its legacy precision analog and power management product lines with full datasheet, simulation model, and application support.

The LT3474/LT3474-1 family was designed specifically for high-fidelity, constant-current LED driving in demanding environments - emphasizing thermal robustness, dimming fidelity, and integration to reduce external component count in commercial and industrial lighting.

FAQ

What is the maximum LED string voltage supported by LT3474IFE-1#PBF?

The LT3474IFE-1#PBF supports LED strings up to 26 V, as specified in its absolute maximum ratings for the OUT/LED pins. This distinguishes it from the standard LT3474 (15 V limit) and enables driving longer series strings - for example, seven 3.7 V white LEDs - while maintaining regulation and protection integrity across the full –40°C to +125°C operating range.

How does LT3474IFE-1#PBF achieve 400:1 dimming without color shift?

The LT3474IFE-1#PBF implements True Color PWM™ by holding LED current amplitude constant during PWM on-cycles and fully disconnecting the control loop (via PWM pin) during off-cycles - preserving VC pin voltage and compensation capacitor charge. This avoids analog current ramping that causes chromaticity drift. The result is linear light output vs. duty cycle with Δu'v' < 0.002 across the full 400:1 range, confirmed in typical performance graphs for LT3474IFE-1#PBF.

Can LT3474IFE-1#PBF operate without an external boost capacitor?

No - LT3474IFE-1#PBF requires an external boost capacitor connected between BOOST and SW pins. The internal Schottky diode charges this capacitor to ~VIN + 1.9 V, providing sufficient gate drive for the internal NPN switch. Omitting it causes switch saturation failure, excessive V_CE(SAT), and thermal shutdown. Typical value is 0.1 μF X7R ceramic placed adjacent to BOOST/SW pins per LT3474IFE-1#PBF layout guidelines.

What is the purpose of the DNC pins (1 and 16) on LT3474IFE-1#PBF?

Pins 1 and 16 of LT3474IFE-1#PBF are designated DNC (Do Not Connect) and must remain floating - not tied to GND, VIN, or any other net. These pins have no internal connection and routing traces or vias to them risks parasitic coupling, noise injection, or mechanical stress on the bond wires. The FE package datasheet explicitly warns against external circuitry on these pins to ensure LT3474IFE-1#PBF reliability and thermal performance.

Does LT3474IFE-1#PBF include open-LED protection?

No - LT3474IFE-1#PBF (the "-1" variant) does not include internal open-LED protection, unlike the base LT3474. If the LED string opens, the LT3474IFE-1#PBF will attempt to regulate at maximum duty cycle, potentially violating the ABSMAX BOOST pin voltage (51 V) or OUT/LED pin rating (26 V). External overvoltage protection - such as a Zener clamp from OUT to GND - is required for fault-safe operation, as shown in Figure 2 of the LT3474IFE-1#PBF datasheet.