Analog Devices Inc. LT3755EMSE-2#PBF

Overview

LT3755EMSE-2#PBF 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 features high-side current sensing (100 mV threshold), 4.5V–40V input range, up to 75V output capability, and supports true-color PWM dimming up to 3000:1 for automotive LED headlamps.

For engineers reviewing the LT3755EMSE-2#PBF datasheet, LT3755EMSE-2#PBF pinout, LT3755EMSE-2#PBF application, or LT3755EMSE-2#PBF equivalent, key selection criteria include its AEC-Q100 qualification, open LED protection with dedicated OPENLED pin, programmable frequency (100 kHz–1 MHz), and dual regulation mode (constant-current and constant-voltage) enabled by ground-referenced FB and ISP/ISN inputs.

Technical Context

The LT3755EMSE-2#PBF implements a fixed-frequency current-mode control architecture with internal 7.15 V INTVCC regulator powering gate driver and logic. Its error amplifier (VC) integrates the difference between ISP–ISN voltage and CTRL-set threshold (100 mV full-scale), enabling precise LED current regulation independent of output topology.

It includes dedicated high-side current sense inputs (ISP/ISN) with short-circuit detection (<3 V common-mode), open LED fault reporting via OPENLED (active-low open-collector), and integrated overvoltage protection that forces PWMOUT low when FB exceeds VFB + 60 mV - all confirmed for the -2 variant per datasheet Rev. E.

Key Specifications

Pinout & Package

LT3755EMSE-2#PBF is housed in a 16-lead plastic MSOP package (3 mm × 4.9 mm) with exposed thermal pad (Pin 17 = GND). The package supports high-power density designs and requires soldering the exposed pad to the PCB ground plane for thermal and electrical integrity.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC3783EFE#PBF and LM3410XSD/NOPB, the LT3755EMSE-2#PBF offers unique AEC-Q100 qualification, programmable frequency, high-side current sensing, and dedicated OPENLED fault signaling - making it the only option among the three validated for automotive headlamp use with full topology flexibility and safety monitoring.

Availability

LT3755EMSE-2#PBF is available at Aetrix Electronics and suitable for automotive LED headlamps, industrial machine vision lighting, and architectural signage requiring stable component supply, long-term lifecycle support, and AEC-Q100-compliant performance.

Supply support for LT3755EMSE-2#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. is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, serving industrial, automotive, communications, and healthcare markets.

The LT3755 product line delivers high-voltage, high-efficiency LED controllers optimized for demanding automotive and industrial lighting applications where reliability, precision current regulation, and fault resilience are critical.

FAQ

What is the key functional difference between LT3755EMSE-2#PBF and the LT3755-1 variants?

The LT3755EMSE-2#PBF includes an OPENLED pin for open-circuit LED fault detection, whereas LT3755-1 variants replace this pin with SYNC for external oscillator synchronization. This makes LT3755EMSE-2#PBF ideal for safety-critical lighting where fault reporting is mandatory, while LT3755-1 suits systems requiring clock alignment across multiple converters. Both share identical current-sense architecture and regulation capabilities.

Does LT3755EMSE-2#PBF support constant-voltage regulation, and how is it configured?

Yes, LT3755EMSE-2#PBF supports constant-voltage regulation using the FB pin, which is internally referenced to 1.25 V. To enable CV mode, connect FB to the output voltage divider - the error amplifier will regulate the output to maintain FB = 1.25 V. When used alongside current regulation, the FB loop dominates during overvoltage events, triggering PWMOUT low to protect LEDs. LT3755EMSE-2#PBF's dual-loop architecture allows seamless transition between CC and CV modes.

What is the minimum recommended value for the RT resistor to achieve 1 MHz switching frequency with LT3755EMSE-2#PBF?

Per the Typical Performance Characteristics (Figure 7), an RT resistor of 10 kΩ sets the switching frequency to approximately 1000 kHz (1 MHz) at 25°C. The LT3755EMSE-2#PBF datasheet confirms this value applies across the full operating temperature range. Use a 1% tolerance metal-film resistor placed close to the RT pin with short traces to GND to minimize noise coupling and ensure stable frequency operation.

How does the CTRL pin affect LED current regulation in LT3755EMSE-2#PBF?

The CTRL pin adjusts the ISP–ISN current sense threshold linearly from 0 to 100 mV for VCTRL between 0 V and 1 V, enabling analog dimming. Above 1.2 V, the threshold remains fixed at 100 mV. For example, at VCTRL = 0.5 V, the threshold is 50 mV, halving the regulated LED current versus full-scale. This direct scaling allows precise thermal derating or brightness tuning without modifying sense resistors. LT3755EMSE-2#PBF uses this to coordinate analog and PWM dimming for smooth low-end response.

Is LT3755EMSE-2#PBF compatible with standard 16-lead MSOP footprints, and what is the thermal pad requirement?

Yes, LT3755EMSE-2#PBF uses the industry-standard 16-lead MSOP package (3 mm × 4.9 mm) with exposed thermal pad (Pin 17). The pad must be soldered to a dedicated PCB copper area connected to GND for thermal dissipation and signal integrity. Analog Devices specifies θJA = 43°C/W for the MSOP package - omitting pad connection degrades thermal performance significantly and may cause premature thermal shutdown. LT3755EMSE-2#PBF's reliability in automotive applications depends on proper pad implementation.