Analog Devices Inc. LT3755IUD-1#TRPBF

Overview

LT3755IUD-1#TRPBF from Analog Devices is a constant-frequency, current-mode DC/DC LED controller driving external N-channel MOSFETs in boost, buck, buck-boost, SEPIC, or flyback topologies. It delivers up to 75V output, supports 4.5V–40V input, provides 100mV high-side current sensing, enables 3000:1 PWM dimming, and features frequency synchronization via SYNC pin. It is used in automotive LED headlamp drivers requiring precise current regulation and fault protection.

For engineers reviewing the LT3755IUD-1#TRPBF datasheet, LT3755IUD-1#TRPBF pinout, LT3755IUD-1#TRPBF application, or LT3755IUD-1#TRPBF equivalent, key selection criteria include its AEC-Q100 qualification, 100kHz–1MHz adjustable switching frequency, open LED and short-circuit protection, programmable undervoltage lockout with hysteresis, and thermally enhanced 3mm × 3mm QFN package with exposed pad.

Technical Context

The LT3755IUD-1#TRPBF implements a fixed-frequency current-mode architecture with internal 7.15V INTVCC regulator powering the gate driver and logic. Its high-side current sense (ISP/ISN) enables topology flexibility, while the SYNC pin allows external clock synchronization-distinguishing it from the base LT3755 and LT3755-2 variants.

It integrates dual feedback loops: one for constant-current regulation via ISP–ISN differential voltage (programmable 0–100mV using CTRL), and another for constant-voltage regulation via FB (1.25V reference). The OPENLED function is replaced by SYNC on this variant, and fault detection includes short-circuit monitoring below 3V common-mode voltage at ISN.

Key Specifications

Pinout & Package

LT3755IUD-1#TRPBF is housed in a thermally enhanced 16-lead plastic QFN (3mm × 3mm) with exposed pad (Pin 17), which must be soldered to PCB ground for thermal management and signal reference. Pin numbering follows standard top-view layout with Pin 1 at top-left corner.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar LED controller applications.

Compared with LT3755IUD#TRPBF and LT3755IUD-2#TRPBF, the LT3755IUD-1#TRPBF trades open-LED reporting for deterministic timing control-making it optimal for noise-sensitive, multi-controller systems where synchronized switching reduces beat frequencies and EMI peaks.

Availability

LT3755IUD-1#TRPBF is available at Aetrix Electronics and suitable for automotive LED headlamps, industrial machine vision lighting, battery-powered portable lighting, and architectural signage requiring stable component supply, AEC-Q100 compliance, and precise current regulation.

Supply support for LT3755IUD-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. is a global semiconductor leader specializing in high-performance analog, mixed-signal, and digital signal processing technologies for precision, power, and connectivity applications.

The LT3755 family is designed for high-power LED driver applications demanding robust protection, topology flexibility, and automotive-grade reliability-targeting front-end lighting, industrial illumination, and high-brightness signage.

FAQ

What distinguishes LT3755IUD-1#TRPBF from the standard LT3755IUD#TRPBF?

The LT3755IUD-1#TRPBF replaces the OPENLED pin with a SYNC pin for external clock synchronization, enabling deterministic timing alignment in multi-converter systems. Unlike the base LT3755IUD#TRPBF, it does not provide open-LED fault reporting but adds EMI-reduction capability through synchronized switching. Both share identical current-sense architecture, 4.5V–40V input range, and AEC-Q100 Grade I qualification. The LT3755IUD-1#TRPBF remains fully pin-compatible with the base part in QFN packaging.

Can LT3755IUD-1#TRPBF operate in buck topology with an input voltage higher than the LED string voltage?

Yes, the LT3755IUD-1#TRPBF supports buck, boost, buck-boost, SEPIC, and flyback configurations. In buck mode, it regulates LED current when VIN exceeds the forward voltage of the LED string. High-side current sensing (via ISP/ISN) decouples the controller's ground reference from the LED cathode, allowing direct connection of the LED string to system ground-a key advantage for automotive implementations. The device maintains stable current regulation across duty cycles and input variations.

What is the role of the CTRL pin on LT3755IUD-1#TRPBF, and how does it affect LED current?

The CTRL pin on LT3755IUD-1#TRPBF programs the ISP–ISN current sense threshold from 0 mV to 100 mV. For 0 V < V_CTRL < 1 V, the threshold is (V_CTRL – 0.1 V)/10; above 1.2 V, it holds at 100 mV. This enables analog dimming and temperature compensation. With a 100 mV threshold and 0.1 Ω sense resistor, LT3755IUD-1#TRPBF delivers 1 A LED current (I_LED = 100 mV / 0.1 Ω). The CTRL pin's 50–100 nA bias current ensures minimal loading on external divider networks.

How does the SYNC functionality work on LT3755IUD-1#TRPBF, and what are the design requirements?

The SYNC pin on LT3755IUD-1#TRPBF accepts an external logic-level clock (100 kHz–1 MHz) to synchronize the internal oscillator. The RT resistor must be selected to set the free-running frequency ~20% lower than the SYNC signal frequency. Gate turn-on occurs after a fixed delay from the SYNC rising edge. For optimal PWM performance, the PWM rising edge should precede the SYNC edge by ≥200 ns. A 50% duty cycle square wave is recommended, and unused SYNC pins must be tied to GND to prevent floating inputs.

Is LT3755IUD-1#TRPBF suitable for AEC-Q100 automotive applications, and which grade does it meet?

Yes, LT3755IUD-1#TRPBF is AEC-Q100 qualified and specified for Grade I operation (–40°C to +125°C junction temperature). It undergoes stress testing for automotive reliability, including temperature cycling, humidity bias, and ESD. The 3mm × 3mm QFN package with exposed thermal pad supports thermal management in compact headlamp modules. All electrical parameters in the datasheet are guaranteed across this temperature range, making LT3755IUD-1#TRPBF appropriate for front lighting, daytime running lamps (DRL), and interior ambient systems.