Analog Devices Inc. LTC3765IMSE#TRPBF

Overview

LTC3765IMSE#TRPBF from Analog Devices (formerly Linear Technology) is a start-up controller and gate driver IC for self-starting secondary-side controlled active clamp forward converters. It integrates high-speed primary (PG) and active clamp (AG) gate drivers, on-chip bridge rectifier for pulse transformer bias extraction, precision UVLO with adjustable hysteresis, linear regulator controller for 35µs VCC ramp-up, and Direct Flux Limit™ circuitry to prevent transformer saturation. It enables isolated 5V/15A power supplies in telecom and server applications.

For engineers reviewing the LTC3765IMSE#TRPBF datasheet, LTC3765IMSE#TRPBF pinout, LTC3765IMSE#TRPBF application, or LTC3765IMSE#TRPBF equivalent, key selection considerations include its 16-lead MSOP package, –40°C to 125°C operating junction temperature, 7.7–14.5V VCC operating range, 150mV overcurrent threshold, and programmable AG-to-PG delay via external resistor on DELAY pin.

Technical Context

The LTC3765IMSE#TRPBF implements a proprietary pulse-encoded communication scheme with the LTC3766 secondary-side controller across an isolation barrier using a small pulse transformer. Its internal bridge rectifier extracts gate drive bias power directly from IN+/IN–, eliminating need for auxiliary bias windings.

It features dual gate drivers: PG delivers 2.5A peak pull-up current with 20ns rise/fall times into 4.7nF load, while AG provides matched timing with fixed 180ns turn-on delay relative to PG. The Direct Flux Limit™ uses RUN pin voltage and RCORE-set slope replication to enforce real-time magnetizing current limits during NMOS on-time, guaranteeing no core saturation even during startup into pre-biased outputs.

Key Specifications

Pinout & Package

Package: 16-lead plastic MSOP (MSE) with exposed thermal pad (Pin 17 = SGND), θ_JA = 45°C/W, θ_JC = 10°C/W. Exposed pad must be soldered to PCB ground plane for thermal performance.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar active clamp forward controller applications.

Compared with LTC3765IMSE#TRPBF, the H-grade variant extends thermal capability to 150°C for harsh environments, while the E-grade reduces cost but sacrifices guaranteed operation below 0°C and above 85°C - both share identical electrical specs, pinout, and feature set.

Availability

LTC3765IMSE#TRPBF is available at Aetrix Electronics and suitable for isolated telecom power, server DC/DC conversion, and industrial embedded power applications requiring stable component supply, long lifecycle support, and guaranteed industrial temperature performance.

Supply support for LTC3765IMSE#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 acquired Linear Technology in 2017 and maintains its high-performance power management portfolio. Linear's legacy includes pioneering isolated controller architectures and precision analog power ICs.

The LTC3765IMSE#TRPBF belongs to Linear's active clamp forward controller product line, designed specifically for high-efficiency, galvanically isolated DC/DC conversion with secondary-side regulation and robust transient handling in telecom and computing infrastructure.

FAQ

What is the primary function of the LTC3765IMSE#TRPBF in an isolated power supply?

The LTC3765IMSE#TRPBF serves as the primary-side start-up controller and gate driver in an active clamp forward converter. It initiates open-loop operation, drives the primary NMOS (via PG) and active clamp PMOS (via AG), extracts bias power from the pulse transformer using its on-chip bridge rectifier, and transfers control to the LTC3766 secondary-side controller once stable operation is achieved. Its core purpose is enabling self-starting, isolated, synchronous forward conversion without auxiliary bias supplies.

How does the Direct Flux Limit™ feature in the LTC3765IMSE#TRPBF prevent transformer saturation?

The LTC3765IMSE#TRPBF implements Direct Flux Limit™ by continuously monitoring magnetizing current during both active clamp conduction (via ISMAG) and primary switch conduction (via RUN voltage and RCORE-scaled slope replication). During the NMOS on-time, it enforces a real-time limit based on an internally generated magnetizing current ramp, preventing flux "walk" during load steps or startup into pre-biased outputs - unlike duty-cycle clamping or loop bandwidth reduction, this method guarantees no saturation without compromising transient response.

What is the role of the DELAY pin on the LTC3765IMSE#TRPBF, and how is it configured?

The DELAY pin on the LTC3765IMSE#TRPBF sets the dead time between AG turn-off and PG turn-on via an external resistor to ground. This programmable overlap is critical for minimizing transitional power loss in the primary NMOS: turning it on when the SWP node voltage reaches VIN (after active clamp discharge) reduces switching losses. Typical values range from 10kΩ to 50kΩ, yielding delays from ~140ns to ~530ns, as specified in the Electrical Characteristics table under t_DPG.

Can the LTC3765IMSE#TRPBF operate without the LTC3766 secondary-side controller?

No - the LTC3765IMSE#TRPBF is designed exclusively for use with the LTC3766. While it performs open-loop start-up using its internal oscillator, full regulation and steady-state operation require pulse-encoded PWM signals received via IN+/IN– from the LTC3766. The LTC3765IMSE#TRPBF lacks internal voltage feedback or error amplification; it relies entirely on the LTC3766 for closed-loop control, fault coordination, and communication lock establishment across the isolation barrier.

What thermal considerations apply to the LTC3765IMSE#TRPBF's exposed pad (Pin 17)?

The exposed pad (Pin 17) of the LTC3765IMSE#TRPBF is electrically and thermally connected to SGND and must be soldered to a PCB ground plane to achieve rated thermal performance. With θ_JA = 45°C/W and θ_JC = 10°C/W, proper pad soldering is essential to maintain junction temperature within the –40°C to 125°C operating range under full load. Failure to solder the pad risks thermal shutdown or accelerated aging, especially in high-power or high-ambient applications.