Analog Devices Inc. LTC3765IMSE#PBF

Overview

LTC3765IMSE#PBF from Analog Devices (formerly Linear Technology) is a self-starting primary-side gate driver and start-up controller for active clamp forward converters, featuring integrated bridge rectifier, precision UVLO, linear regulator controller, and Direct Flux Limit™ architecture. It delivers 11V PG high output, 2.5A peak pull-up current, and supports 36V–72V input to 5V/15A isolated output in telecom and server power supplies.

For engineers reviewing the LTC3765IMSE#PBF datasheet, LTC3765IMSE#PBF pinout, LTC3765IMSE#PBF application, or LTC3765IMSE#PBF equivalent, key selection considerations include active clamp delay adjustment (120–530 ns), ISMAG-based magnetizing current limiting, RCORE-configurable flux slope replication, and compatibility with LTC3766 secondary-side control for galvanically isolated synchronous forward topologies.

Technical Context

The LTC3765IMSE#PBF implements a proprietary pulse-encoded communication scheme over a small pulse transformer to receive duty-cycle commands from the LTC3766, enabling secondary-side regulation while maintaining primary-side gate drive control. Its on-chip bridge rectifier extracts VCC bias power directly from IN+/IN–, eliminating external auxiliary supplies.

It integrates a linear regulator controller driving NDRV to ramp VCC with 35µs rise time, plus a fixed 180ns AG turn-on delay and programmable PG rising delay (120–530 ns via DELAY pin resistor). The Direct Flux Limit™ uses RUN-pin voltage and RCORE-set slope to replicate transformer magnetizing current during NMOS on-time, preventing saturation without sacrificing transient response.

Key Specifications

Pinout & Package

16-lead plastic MSOP package with exposed thermal pad (Pin 17) tied to SGND. Requires PCB thermal plane connection for rated 150°C junction temperature operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UCC2897A and LM5045, the LTC3765IMSE#PBF uniquely integrates pulse-transformer-powered VCC generation, programmable AG-PG delay, and Direct Flux Limit™-enabling single-chip saturation-free startup into pre-biased outputs without auxiliary windings or external slope-setting components.

Availability

LTC3765IMSE#PBF is available at Aetrix Electronics and suitable for isolated telecom power supplies, server DC/DC converters, and industrial embedded power systems requiring stable component supply, long-term lifecycle support, and guaranteed -40°C to 125°C operation.

Supply support for LTC3765IMSE#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 high-performance analog and power management portfolio. Linear Technology was renowned for precision power ICs with robust protection and innovative control architectures.

The LTC3765IMSE#PBF belongs to Linear's isolated forward controller product line, designed specifically for self-starting, secondary-regulated active clamp topologies in telecom, server, and industrial power systems where transformer saturation avoidance and minimal external components are critical.

FAQ

What is the function of the ISMAG pin on the LTC3765IMSE#PBF?

The ISMAG pin on the LTC3765IMSE#PBF senses voltage across a current sense resistor in series with the active clamp PMOS source. It enables the Direct Flux Limit™ feature by directly monitoring magnetizing current during the clamp phase, allowing the LTC3765IMSE#PBF to prevent transformer core saturation during load transients and pre-biased startup without compromising transient response.

How does the LTC3765IMSE#PBF achieve self-starting without an auxiliary bias supply?

The LTC3765IMSE#PBF achieves self-starting by integrating an on-chip bridge rectifier that extracts DC bias power from the pulse-encoded signal received on IN+ and IN– pins from the LTC3766. This eliminates the need for a separate auxiliary winding or bias supply, reducing component count and board space while ensuring reliable startup across the full 36V–72V input range.

What is the purpose of the RCORE pin on the LTC3765IMSE#PBF?

The RCORE pin on the LTC3765IMSE#PBF connects to a resistor that configures the internal slope replicator for transformer magnetizing current. Combined with RUN pin voltage, it generates an accurate real-time estimate of flux accumulation during the primary NMOS on-time-enabling the Direct Flux Limit™ to guarantee no saturation even during rapid duty cycle changes or pre-biased output startup.

Can the LTC3765IMSE#PBF operate independently without the LTC3766?

No-the LTC3765IMSE#PBF is designed exclusively for use with the LTC3766 secondary-side controller. While it performs open-loop start-up using its internal oscillator, full regulation and dynamic control require pulse-encoded feedback from the LTC3766 via IN+/IN–. The LTC3765IMSE#PBF lacks internal voltage feedback loop compensation and relies entirely on the LTC3766 for closed-loop operation.

What protection features are built into the LTC3765IMSE#PBF?

The LTC3765IMSE#PBF includes overcurrent protection (via IS+/IS– differential sensing), overtemperature shutdown (165°C trip with 20°C hysteresis), VCC undervoltage lockout (7.1V rising/7.0V falling), RUN pin UVLO (1.25V threshold), and communication loss detection with the LTC3766. All faults trigger immediate switching halt and pull the SSFLT pin above 5.75V for system-level fault signaling.