Analog Devices Inc. LTC3728LCGN#TRPBF

Overview

LTC3728LCGN#TRPBF from Analog Devices (formerly Linear Technology) is a dual-phase, synchronous step-down controller IC driving two independent N-channel MOSFET stages in 180° out-of-phase operation. It delivers precise 0.8V reference accuracy (±1%), supports 4.5V–28V input, operates up to 550kHz, and integrates dual 5V/3.3V standby regulators - used in high-efficiency notebook CPU core power supplies.

For engineers reviewing the LTC3728LCGN#TRPBF datasheet, LTC3728LCGN#TRPBF pinout, LTC3728LCGN#TRPBF application, or LTC3728LCGN#TRPBF equivalent, key selection criteria include phase-interleaved input ripple reduction, OPTI-LOOP compensation for wide output capacitor/ESR tolerance, programmable operating mode (Burst/Constant-Frequency/PWM), and dual-channel power-good monitoring with ±7.5% window.

Technical Context

The LTC3728LCGN#TRPBF implements a constant-frequency current-mode control architecture with dual independent error amplifiers, transconductance gm = 1.3 mmho, and gain-bandwidth of 3 MHz per channel. Its phase-locked loop accepts external synchronization via PLLIN and enables frequency tuning from 260kHz to 550kHz using a DC voltage on PLLFLTR.

Each channel features dedicated ITH pins for current limit programming, VOSENSE feedback inputs with 0.792–0.808V regulation range, and integrated overvoltage protection that latches the bottom MOSFET until recovery. The RUN/SS pins provide soft-start ramping (1.2µA charge current) and configurable short-circuit latchoff timing.

Key Specifications

Pinout & Package

Package: 28-Lead Narrow Plastic SSOP (GN), exposed pad not present - suitable for standard surface-mount assembly with θJA = 95°C/W.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual-phase synchronous buck controller applications.

Compared with LTC3728LCGN#TRPBF, LTC3728LEGN#TRPBF offers broader temperature qualification without functional trade-offs, while LTC3728LCUH#TRPBF delivers superior thermal resistance in a smaller footprint - both retain identical control architecture, pin compatibility, and feature set.

Availability

LTC3728LCGN#TRPBF is available at Aetrix Electronics and suitable for notebook computing, telecom power distribution, and portable instrumentation requiring stable component supply, consistent parametric performance, and long-term production continuity.

Supply support for LTC3728LCGN#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 full product support, documentation, and manufacturing continuity for the LTC portfolio.

The LTC3728L series was designed specifically for high-efficiency, dual-phase synchronous buck conversion in space- and thermally-constrained portable and computing applications - emphasizing input ripple reduction, light-load efficiency, and robust protection.

FAQ

What is the maximum supported switching frequency for the LTC3728LCGN#TRPBF?

The LTC3728LCGN#TRPBF supports a maximum switching frequency of 550kHz when the PLLFLTR pin voltage is ≥2.4V. This upper limit is guaranteed across the full 0°C to +85°C operating temperature range and enables high-frequency operation to minimize passive component size in compact power designs. The LTC3728LCGN#TRPBF achieves this using an internal phase-locked oscillator whose frequency scales linearly with PLLFLTR voltage.

Does the LTC3728LCGN#TRPBF support external synchronization, and how is it implemented?

Yes, the LTC3728LCGN#TRPBF supports external synchronization via the PLLIN pin, which connects to an internal phase detector. When a clean clock signal is applied to PLLIN, the internal oscillator locks its rising edge to the PLLIN rising edge, enabling precise timing alignment across multiple converters. The PLLIN pin is internally terminated with 50kΩ to SGND, and the lock range covers frequencies matching the internal oscillator's 260kHz–550kHz span. The LTC3728LCGN#TRPBF maintains synchronization even under varying load or input conditions.

How does the FCB pin affect operating mode selection in the LTC3728LCGN#TRPBF?

The FCB pin on the LTC3728LCGN#TRPBF selects among three distinct operating modes: pulling FCB <0.8V forces continuous PWM operation; setting FCB between 0.8V and (INTVCC – 2V) enables Burst Mode for high light-load efficiency; tying FCB to INTVCC disables Burst Mode and enforces constant-frequency discontinuous conduction. These modes directly impact efficiency, output ripple, and EMI profile - the LTC3728LCGN#TRPBF's behavior is fully determined by the DC voltage applied to FCB without requiring additional control signals.

What protection features are integrated into the LTC3728LCGN#TRPBF?

The LTC3728LCGN#TRPBF integrates output overvoltage protection (latching bottom MOSFET until recovery), foldback current limiting during output faults, short-circuit latchoff timed by RUN/SS capacitor discharge, and undervoltage lockout (UVLO) at 3.5V (rising) / 4.0V (falling). It also includes thermal shutdown and internal driver current limits. All protections operate autonomously without external components - the LTC3728LCGN#TRPBF ensures safe operation during startup, overload, or input transients while maintaining system reliability.

Can the LTC3728LCGN#TRPBF regulate a secondary winding, and how is this achieved?

Yes, the LTC3728LCGN#TRPBF can regulate a secondary winding using the FCB pin: pulling FCB below 0.8V forces both controllers into continuous PWM mode, enabling synchronous rectification and precise voltage regulation of an auxiliary winding - commonly used for EXTVCC generation or isolated bias supplies. This function is explicitly documented in the LTC3728LCGN#TRPBF datasheet and requires no additional ICs or feedback circuitry, leveraging the existing error amplifier and current-sense infrastructure.