Analog Devices Inc. LTC3765EMSE#PBF

Overview

LTC3765EMSE#PBF from Analog Devices (formerly Linear Technology) is a self-starting primary-side gate driver and start-up controller for active clamp forward converters, designed to operate with the LTC3766 secondary-side controller. It integrates high-speed NMOS/PMOS gate drivers (PG/AG), on-chip bridge rectifier for pulse-transformer bias extraction, precision UVLO (7.1V rising / 6.7V falling), linear regulator controller (8.5V output), and Direct Flux Limit™ core saturation protection. It enables isolated 36V–72V to 5V/15A power supplies in telecom and server applications.

For engineers reviewing the LTC3765EMSE#PBF datasheet, LTC3765EMSE#PBF pinout, LTC3765EMSE#PBF application, or LTC3765EMSE#PBF equivalent, key selection considerations include active clamp delay tuning via DELAY pin resistor, ISMAG/RCORE-based magnetizing current slope replication, PG/AG timing coordination, VCC startup ramp control via NDRV, and fault signaling through SSFLT pin voltage >5.75V.

Technical Context

The LTC3765EMSE#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 with galvanic isolation. Its internal bridge rectifier on IN+/IN− extracts gate drive bias power directly from the encoded signal, eliminating external bias windings.

It employs Direct Flux Limit™-a dual-path flux monitoring method: direct sensing of magnetizing current during active clamp conduction (via ISMAG), and real-time slope replication during primary switch conduction (using RUN voltage and RCORE-set time constant). This guarantees no transformer saturation during load transients or pre-biased startup without degrading transient response.

Key Specifications

Pinout & Package

Package: 16-lead plastic MSOP (MSE) with exposed thermal pad (Pin 17 = SGND). Requires PCB ground plane connection for θJA = 45°C/W thermal performance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UCC28950PWPR and LM5035MTX/NOPB, the LTC3765EMSE#PBF uniquely integrates pulse-transformer bias extraction, Direct Flux Limit™, and seamless LTC3766 handoff - making it the only solution qualified for high-reliability isolated forward converters demanding guaranteed no-saturation operation under worst-case transients.

Availability

LTC3765EMSE#PBF is available at Aetrix Electronics and suitable for isolated telecom power supplies, server DC/DC converters, and industrial battery chargers requiring stable component supply, long-term lifecycle support, and guaranteed industrial-temperature operation.

Supply support for LTC3765EMSE#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) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving industrial, automotive, communications, and computing markets.

The LTC3765EMSE#PBF belongs to Linear's isolated power controller product line, engineered specifically for high-efficiency, self-starting active clamp forward converters requiring secondary-side regulation, transformer saturation immunity, and minimal external components.

FAQ

What is the function of the ISMAG pin on the LTC3765EMSE#PBF?

The ISMAG pin on the LTC3765EMSE#PBF senses the voltage across a current sense resistor placed in series with the source of the active clamp PMOS. During active clamp conduction, this measurement directly limits magnetizing current to prevent transformer core saturation. It is a critical input for the Direct Flux Limit™ system and must be connected with low-inductance routing to maintain accuracy under fast transients.

How does the LTC3765EMSE#PBF achieve self-starting without an auxiliary bias supply?

The LTC3765EMSE#PBF achieves self-starting by integrating an on-chip bridge rectifier across the IN+ and IN− pins. When the LTC3766 begins pulsing the pulse transformer during initial power-up, the rectifier extracts DC bias power directly from the encoded signal and delivers it to the VCC pin - eliminating the need for a separate bias winding or auxiliary supply.

What is the purpose of the DELAY pin on the LTC3765EMSE#PBF?

The DELAY pin on the LTC3765EMSE#PBF sets the dead time between AG (active clamp PMOS) turn-off and PG (primary NMOS) turn-on via an external resistor to ground. This programmable overlap is essential for minimizing transitional switching losses in active clamp forward converters by aligning PG turn-on with the minimum voltage at the SWP node.

How does the Direct Flux Limit™ feature of the LTC3765EMSE#PBF prevent transformer saturation?

The Direct Flux Limit™ in the LTC3765EMSE#PBF prevents transformer saturation using two complementary methods: (1) direct sensing of magnetizing current during active clamp conduction via ISMAG, and (2) real-time replication of the magnetizing current slope during primary conduction using RUN voltage and RCORE-set calibration. This dual-path approach guarantees no saturation even during pre-biased startup or large load transients.

What happens when a fault occurs on the LTC3765EMSE#PBF?

When a fault occurs - such as overcurrent, overtemperature, VCC UVLO, RUN undervoltage, or loss of communication with LTC3766 - the LTC3765EMSE#PBF immediately disables PG and AG outputs and pulls the SSFLT pin above 5.75V. This signals fault condition, halts switching, and initiates coordinated restart once SSFLT discharges to 0.7V - unless locked out via external Zener diode.