Analog Devices Inc. LTC3728LEUH-1#PBF

Overview

LTC3728LEUH-1#PBF from Analog Devices (formerly Linear Technology) is a dual-phase, 550kHz synchronous step-down controller driving all-N-channel MOSFET stages in high-efficiency DC/DC converters. It features 180° out-of-phase operation, OPTI-LOOP® compensation, ±1.5% output voltage accuracy, and a 4.5V–28V input range. It is used in notebook computers and telecom systems to reduce input ripple and EMI while supporting dual 5V/3.3V outputs at up to 5A each.

For engineers reviewing the LTC3728LEUH-1#PBF datasheet, LTC3728LEUH-1#PBF pinout, LTC3728LEUH-1#PBF application, or LTC3728LEUH-1#PBF equivalent, key selection criteria include phase-interleaved current mode control, absence of overcurrent latchoff, FCB-selectable operating modes (Burst Mode®, constant frequency, PWM), and compatibility with 5mm × 5mm QFN packaging for compact power delivery designs.

Technical Context

The LTC3728LEUH-1#PBF implements two independent current-mode control loops with 180° phase offset, enabling interleaved operation that cuts RMS input current by ~39% versus single-phase dual controllers. Its constant-frequency architecture supports PLL synchronization via PLLIN and programmable oscillator frequency (260–550kHz) through PLLFLTR voltage control.

Each channel integrates dedicated error amplifiers (ITH1/ITH2), differential current sense comparators (SENSE1±/SENSE2±), and gate drivers (TG1/BG1/TG2/BG2) with 55ns rise/fall times. The device lacks overcurrent latchoff-unlike the LTC3728L-and includes a 3.3V linear regulator (10mA), PGOOD open-drain indicator, and dual RUN/SS pins for independent soft-start control.

Key Specifications

Pinout & Package

Package: 32-lead (5mm × 5mm) plastic QFN (UH package) with exposed pad (Pin 33) soldered to PCB for thermal and signal ground. Operating temperature range: –40°C to +85°C.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC3728LEGN-1#PBF, the LTC3728LEUH-1#PBF offers 64% smaller PCB area and 64% lower thermal resistance (θJA = 34°C/W), while LTC3728LIUH-1#PBF adds production-grade temperature assurance without altering footprint or function - making the -E variant optimal for cost-sensitive commercial designs with relaxed qualification rigor.

Availability

LTC3728LEUH-1#PBF is available at Aetrix Electronics and suitable for notebook computers, telecom power systems, and portable instrumentation requiring stable component supply, dual-rail synchronous conversion, and phase-interleaved EMI reduction.

Supply support for LTC3728LEUH-1#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 product support, datasheets, and application engineering for all Linear-branded power ICs including the LTC3728 series.

The LTC3728L-1 family was designed for high-density, high-efficiency dual-output DC/DC conversion in portable and battery-powered systems - emphasizing phase interleaving, low IQ, and flexible mode control without sacrificing precision or reliability.

FAQ

What is the key functional difference between LTC3728LEUH-1#PBF and LTC3728L-1?

The LTC3728LEUH-1#PBF is identical to the LTC3728L-1 in all electrical and functional specifications except that it lacks the overcurrent latchoff feature. This means the LTC3728LEUH-1#PBF automatically recovers from overcurrent events without requiring a reset signal or power cycle, simplifying fault-handling in battery-powered systems where manual intervention is impractical.

Does LTC3728LEUH-1#PBF support external frequency synchronization?

Yes, LTC3728LEUH-1#PBF supports external synchronization via the PLLIN pin. When an external clock signal is applied, the internal phase-locked loop aligns the rising edge of TG1 with the rising edge of the PLLIN signal. The PLLFLTR pin serves as both the phase detector output and DC frequency tuning input, allowing precise oscillator adjustment from 260kHz to 550kHz.

What are the thermal considerations for LTC3728LEUH-1#PBF in continuous operation?

LTC3728LEUH-1#PBF uses a 32-lead 5mm × 5mm QFN package with an exposed thermal pad (Pin 33) that must be soldered to PCB ground. Its θJA is 34°C/W. At 125°C maximum junction temperature and 85°C ambient, it can dissipate up to 1.18W continuously. Adequate copper area (≥250 mm²) under the pad and 4+ thermal vias are required to maintain safe operation under full 5A/channel load.

Can LTC3728LEUH-1#PBF regulate a secondary winding using the FCB pin?

Yes, LTC3728LEUH-1#PBF supports secondary-side regulation via the FCB pin. When FCB is pulled below 0.8V, both controllers enter forced continuous PWM mode, enabling regulation of an auxiliary winding (e.g., transformer-coupled 3.3V rail) by feeding its sensed voltage into VOSENSE2 while maintaining primary 5V output on VOSENSE1 - a technique documented in Linear's Application Note 118.

Is the 3.3VOUT pin on LTC3728LEUH-1#PBF internally current-limited?

Yes, the 3.3VOUT pin on LTC3728LEUH-1#PBF is internally current-limited to 10mA DC with 50mA peak capability. It includes thermal foldback and short-circuit protection. Under sustained 10mA load, output voltage remains within ±2% line/load regulation; leakage in shutdown is ≤50μA, ensuring minimal battery drain in portable applications using LTC3728LEUH-1#PBF.