Analog Devices Inc. LTC3766HUFD#PBF

Overview

LTC3766HUFD#PBF from Analog Devices (formerly Linear Technology) is a secondary-side synchronous forward controller IC designed for isolated active-clamp DC/DC converters. It delivers precise average current limiting (±5 mV threshold accuracy), Direct Flux Limit™ protection against transformer saturation, and clean pre-biased load start-up - enabling high-efficiency (94% at 48V_IN/15A_OUT) battery charger designs in telecom and industrial systems.

For engineers reviewing the LTC3766HUFD#PBF datasheet, LTC3766HUFD#PBF pinout, LTC3766HUFD#PBF application, or LTC3766HUFD#PBF equivalent, key selection criteria include its 28-pin 4mm × 5mm QFN package with exposed thermal pad, –40°C to 150°C operating junction temperature, dual-mode linear regulator control (LV/HV), and PolyPhase®-capable phase synchronization via FS/SYNC pin.

Technical Context

The LTC3766HUFD#PBF implements secondary-side PWM control using a precision error amplifier (2.7 mS transconductance) and fast average current sensing with ripple cancellation via IPK pin. Its Direct Flux Limit™ circuit monitors volt-second product on VSEC pin to terminate PWM on-time before transformer saturation, preserving transient response without compromising safety.

It integrates dual gate drivers (FG/SG with 1.0–1.5 Ω pull-down/pull-up), pulse transformer encoding outputs (PT+/PT–), true remote differential sensing (VS+/VS–/VSOUT), and adaptive shoot-through prevention tied to SW node monitoring - all coordinated through a PLL-synchronizable oscillator (100–500 kHz range) and MODE-selectable LV/HV bias regulation.

Key Specifications

Pinout & Package

The LTC3766HUFD#PBF is housed in a 28-lead, 4mm × 5mm plastic QFN package with exposed thermal pad (Pin 29 = GND), optimized for high-power density and thermal performance in isolated power supplies.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar secondary-side synchronous forward controller applications.

Compared with LTC3766IUFD#PBF and LTC3766EUFD#PBF, the LTC3766HUFD#PBF offers extended high-temperature operation (150°C J_MAX), tighter thermal resistance (θ_JA = 43°C/W), and qualification for harsh-environment applications where bias stability and long-term reliability under thermal stress are critical.

Availability

LTC3766HUFD#PBF is available at Aetrix Electronics and suitable for isolated telecom power supplies, high-power battery chargers, avionics DC/DC converters, and military vehicle power systems requiring stable component supply and long lifecycle support.

Supply support for LTC3766HUFD#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 full technical and manufacturing continuity for the LTC portfolio, including precision power management ICs with military- and aerospace-grade qualifications.

The LTC3766HUFD#PBF belongs to Linear's isolated power controller family, engineered specifically for high-efficiency, high-reliability secondary-side control in active-clamp forward converters used in telecom, battery charging, and defense systems.

FAQ

What is the maximum operating junction temperature for the LTC3766HUFD#PBF?

The LTC3766HUFD#PBF is specified for an operating junction temperature range of –40°C to +150°C. This H-grade rating enables reliable operation in high-ambient environments such as engine compartments, industrial enclosures, and avionics bays where thermal derating of lower-grade variants would compromise performance. The 4mm × 5mm QFN package with exposed pad achieves θ_JA = 43°C/W, supporting this extended temperature capability.

How does the Direct Flux Limit™ feature prevent transformer saturation in the LTC3766HUFD#PBF?

The LTC3766HUFD#PBF implements Direct Flux Limit™ by continuously integrating the volt-second product across the main transformer via the VSEC pin. When the integrated voltage exceeds an internal threshold (±4% accuracy), the PWM on-time is immediately terminated - halting energy transfer before core saturation occurs. This hardware-level protection operates independently of loop bandwidth, preserving fast transient response while guaranteeing magnetic safety under line surges, load steps, or startup faults.

Can the LTC3766HUFD#PBF operate without the LTC3765 primary-side controller?

Yes - the LTC3766HUFD#PBF supports standalone operation when the MODE pin is pulled to GND through a 100kΩ (LV) or 50kΩ (HV) resistor. In this mode, PT+ outputs a standard PWM signal for direct primary MOSFET drive, PT– generates a reference clock, and FGD is ignored. However, full isolated forward functionality - including active clamp reset, pulse-encoded communication, and self-starting architecture - requires pairing with the LTC3765 as specified in the reference design.

What is the purpose of the REGSD pin on the LTC3766HUFD#PBF?

The REGSD pin on the LTC3766HUFD#PBF serves as a timer-controlled shutdown input for the high-voltage linear regulator. A capacitor from REGSD to GND sets the maximum allowable activation time for the VIN-based regulator. When the voltage on REGSD reaches 1.21 V (sourced at 13 µA), the regulator disables - preventing indefinite operation if VAUX fails to reach its switchover threshold (4.7 V LV / 7.7 V HV). This protects against thermal runaway during bias supply faults.

Does the LTC3766HUFD#PBF support PolyPhase® operation, and how is it configured?

Yes, the LTC3766HUFD#PBF supports PolyPhase® operation for interleaved multi-phase forward converters. Configuration requires connecting the PHASE pin to set relative clock phasing and using the FS/SYNC pin for PLL synchronization across phases (100–500 kHz range). Multiple LTC3766HUFD#PBF controllers can be synchronized to reduce input/output ripple, distribute thermal load, and scale output current beyond single-phase limits - as validated in Linear's reference design LTC3766 TA01.