Analog Devices Inc. LTC3851AEUD-1#TRPBF

Overview

LTC3851AEUD-1#TRPBF from Analog Devices (formerly Linear Technology) is a high-performance synchronous step-down switching regulator controller driving dual N-channel MOSFETs in constant-frequency current-mode operation. It delivers ±1% output voltage accuracy, supports 4V–38V input, regulates to 0.8V–5.5V outputs, and features phase-lockable 250kHz–750kHz switching with OPTI-LOOP® compensation. It is used in telecom intermediate bus converters requiring precise tracking, soft-start, and robust overvoltage protection.

For engineers reviewing the LTC3851AEUD-1#TRPBF datasheet, LTC3851AEUD-1#TRPBF pinout, LTC3851AEUD-1#TRPBF application, or LTC3851AEUD-1#TRPBF equivalent, key selection criteria include its PGOOD output replacement of ILIM, 16-pin 3mm × 3mm QFN package with exposed thermal pad, 99% duty cycle capability, and selectable light-load modes (Burst Mode®, pulse-skipping, or forced CCM).

Technical Context

The LTC3851AEUD-1#TRPBF implements a constant-frequency current-mode control architecture with an internal transconductance error amplifier (gm = 2 mmho, GBW = 3 MHz), precision 0.8V reference (±1% over –40°C to 125°C), and integrated 5V INTVCC LDO. Its OPTI-LOOP® compensation minimizes required output capacitance across wide ESR ranges.

It uses dual gate drivers (TG/BG) with matched 25ns rise/fall times, 30ns dead-time control, and built-in dropout detection enabling 99% duty cycle. The MODE/PLLIN pin selects operating mode or accepts external synchronization up to 750kHz, while FREQ/PLLFLTR sets oscillator frequency via external resistor.

Key Specifications

Pinout & Package

Package: 16-lead (3mm × 3mm) plastic QFN with exposed thermal pad (Pin 17 = GND). Requires soldering of exposed pad to PCB ground plane for thermal performance and electrical integrity.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC3851AEUD-1#TRPBF, the LTC3851AIMSE-1#TRPBF offers better thermal performance in less demanding layouts, while the MP2918GL-Z trades configurability and wide-input capability for monolithic simplicity and reduced bill-of-materials - making it viable only for fixed-voltage, low-current applications.

Availability

LTC3851AEUD-1#TRPBF is available at Aetrix Electronics and suitable for telecom infrastructure, industrial automation, and automotive infotainment systems requiring stable component supply, long-term lifecycle support, and guaranteed automotive-grade temperature compliance.

Supply support for LTC3851AEUD-1#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 its high-performance power management portfolio with rigorous qualification and long-term product support.

The LTC3851A-1 family is designed for high-efficiency, wide-input synchronous buck controllers targeting telecom, industrial, and automotive applications where precision regulation, robust protection, and flexible sequencing are essential.

FAQ

What is the function of the PGOOD pin on the LTC3851AEUD-1#TRPBF?

The PGOOD pin on the LTC3851AEUD-1#TRPBF is an open-drain output that signals valid regulation: it pulls low when the VFB voltage deviates more than ±10% from the 0.8V reference, during startup, shutdown, or soft-start. Once VFB stabilizes within tolerance, PGOOD goes high (with external pull-up), enabling system-level power sequencing. The LTC3851AEUD-1#TRPBF includes a 17µs power-bad mask to suppress false triggers during transients.

How does the LTC3851AEUD-1#TRPBF achieve 99% duty cycle operation?

The LTC3851AEUD-1#TRPBF achieves 99% duty cycle via integrated dropout detection: when VIN approaches VOUT and the controller attempts continuous top-FET conduction, it forces the top MOSFET off for ~10% of each cycle to recharge the BOOST capacitor. This maintains gate drive integrity without external circuitry. The LTC3851AEUD-1#TRPBF's internal logic ensures this behavior occurs only during true dropout, preserving regulation down to VIN = VOUT + 0.1V.

Can the LTC3851AEUD-1#TRPBF synchronize to an external clock, and what are the requirements?

Yes, the LTC3851AEUD-1#TRPBF can synchronize to an external clock applied to the MODE/PLLIN pin (Pin 15) across 250kHz–750kHz. When synchronized, it operates in forced continuous conduction mode. A series RC network must be connected from FREQ/PLLFLTR (Pin 16) to GND to serve as the PLL loop filter. The LTC3851AEUD-1#TRPBF requires the external clock to be present before RUN enable unless a parallel resistor is added to prevent low-frequency startup glitches.

What is the difference between the LTC3851AEUD-1#TRPBF and the standard LTC3851A-1?

The LTC3851AEUD-1#TRPBF is the E-grade (–40°C to 125°C), QFN-packaged variant of the LTC3851A-1 family. Its key functional distinction versus the base LTC3851A-1 is the replacement of the ILIM pin with PGOOD - enabling direct power-good monitoring instead of adjustable current limit. All timing, compensation, and control features remain identical. The LTC3851AEUD-1#TRPBF shares the same pinout and electrical specs as other LTC3851A-1 variants but is optimized for compact, thermally efficient layouts.

Does the LTC3851AEUD-1#TRPBF support both RSENSE and DCR current sensing?

Yes, the LTC3851AEUD-1#TRPBF supports both RSENSE and DCR current sensing via its differential SENSE+ and SENSE– inputs (Pins 6 and 5). RSENSE offers higher accuracy for current limiting, while DCR sensing eliminates power loss and cost of discrete shunts - ideal for high-current applications. The LTC3851AEUD-1#TRPBF's current foldback and peak-current control operate identically in both configurations, with design guidance provided in the Applications Information section of its datasheet.