Analog Devices Inc. LTC3851AIGN#TRPBF

Overview

LTC3851AIGN#TRPBF from Analog Devices (formerly Linear Technology) is a high-performance synchronous step-down switching regulator controller driving dual N-channel MOSFETs in a constant-frequency current-mode architecture. It operates from 4V to 38V input, delivers 0.8V–5.5V output with ±1% accuracy, supports phase-lockable 250kHz–750kHz switching, and enables Burst Mode™, pulse-skipping, or forced continuous conduction-used in telecom power supplies requiring tight transient response and high efficiency at light loads.

For engineers reviewing the LTC3851AIGN#TRPBF datasheet, LTC3851AIGN#TRPBF pinout, LTC3851AIGN#TRPBF application, or LTC3851AIGN#TRPBF equivalent, key selection criteria include its OPTI-LOOP® compensation for wide output capacitor/ESR tolerance, adjustable current foldback via ILIM pin, 99% duty cycle capability for low-dropout operation, and thermally enhanced 16-lead narrow SSOP package with exposed pad.

Technical Context

The LTC3851AIGN#TRPBF implements a constant-frequency current-mode control loop where peak inductor current is set by the ITH voltage, and output regulation is maintained via an error amplifier comparing VFB to a precision 0.8V reference. Its transconductance amplifier (gm = 2 mmho, GBW = 3 MHz) enables stable loop compensation across diverse output capacitance and ESR values.

It integrates a 5V internal LDO (INTVCC), dual gate drivers with matched rise/fall times (25 ns), dead-time control (30 ns), and a phase-locked loop that accepts external synchronization on MODE/PLLIN while allowing frequency programming via FREQ/PLLFLTR resistor. The IC features undervoltage lockout (3.25V on INTVCC), overvoltage protection (>7.5% above regulated VFB), and shutdown IQ of 20 µA.

Key Specifications

Pinout & Package

Package: 16-lead narrow plastic SSOP (GN package), thermally enhanced with exposed GND pad (Pin 17), rated for –40°C to +125°C junction temperature (θJA = 110°C/W).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC3851IGN#TRPBF, the LTC3851AIGN#TRPBF offers tighter frequency stability under synchronization and improved transient response; versus LTC3891EMSE#TRPBF, it trades integrated bias capability for smaller footprint and lower cost in 38V-max systems.

Availability

LTC3851AIGN#TRPBF is available at Aetrix Electronics and suitable for telecom power supplies, industrial PLC modules, and automotive infotainment systems requiring stable component supply, long-term lifecycle support, and guaranteed parametric performance across –40°C to +125°C.

Supply support for LTC3851AIGN#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, Inc. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving industrial, automotive, communications, and healthcare markets.

The LTC3851A series belongs to Linear's high-efficiency synchronous controller product line, designed specifically for demanding POL applications where precision regulation, wide input range, and adaptive light-load efficiency are critical.

FAQ

What is the function of the ILIM pin on the LTC3851AIGN#TRPBF?

The ILIM pin on the LTC3851AIGN#TRPBF is a tri-level logic input that selects the maximum current sense threshold: grounding it sets 30mV, floating sets 50mV, and connecting to INTVCC sets 75mV. This directly configures the current-limit threshold for overload and short-circuit protection without external components, enabling precise matching to RSENSE or DCR sensing networks in the LTC3851AIGN#TRPBF design.

Can the LTC3851AIGN#TRPBF synchronize to an external clock, and how is it configured?

Yes, the LTC3851AIGN#TRPBF can synchronize to an external clock via the MODE/PLLIN pin. When an external clock signal (250kHz–750kHz) is applied to MODE/PLLIN, the internal phase-locked loop locks to it, forcing the controller into forced continuous conduction mode. A series RC network must be connected from FREQ/PLLFLTR to GND to serve as the PLL loop filter; this configuration ensures jitter-free operation and enables interleaving in multi-phase systems using the LTC3851AIGN#TRPBF.

What is the purpose of the TK/SS pin on the LTC3851AIGN#TRPBF, and how does it affect startup?

The TK/SS pin on the LTC3851AIGN#TRPBF controls output voltage ramping during startup and enables supply tracking. An internal 1µA current charges an external capacitor connected to TK/SS, generating a linear voltage ramp. The LTC3851AIGN#TRPBF regulates VFB to match TK/SS voltage (not 0.8V) until TK/SS reaches 0.8V, ensuring smooth, controlled VOUT rise. It also supports ratiometric or coincident tracking of another supply by connecting a resistor divider to TK/SS.

How does the LTC3851AIGN#TRPBF handle output overvoltage conditions?

The LTC3851AIGN#TRPBF includes dedicated output overvoltage protection (OVP) that triggers when VFB exceeds the regulated value by >7.5%. Upon detection, the top MOSFET is immediately turned off and the bottom MOSFET is forced on to sink current and clamp the output voltage. This hardware-level protection operates independently of the main control loop and safeguards downstream loads such as FPGAs or memory in systems using the LTC3851AIGN#TRPBF, even during transient faults or feedback loop failure.

What package type and thermal characteristics apply to the LTC3851AIGN#TRPBF?

The LTC3851AIGN#TRPBF uses a 16-lead narrow plastic SSOP (GN package) with an exposed GND pad (Pin 17) that must be soldered to the PCB for thermal performance. Its thermal resistance is θJA = 110°C/W (standard JEDEC high-K board), and it is rated for –40°C to +125°C operating junction temperature. The exposed pad significantly improves heat dissipation compared to standard SSOP, making the LTC3851AIGN#TRPBF suitable for high-power-density applications without additional heatsinking.