Analog Devices Inc. LTC3851AIUD-1#TRPBF

Overview

LTC3851AIUD-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 topology. It operates from 4V to 38V input, delivers 0.8V–5.5V output with ±1% accuracy, supports phase-lockable 250kHz–750kHz switching, and features PGOOD monitoring and OPTI-LOOP® compensation - used in telecom intermediate bus converters requiring precise voltage regulation and fast transient response.

For engineers reviewing the LTC3851AIUD-1#TRPBF datasheet, LTC3851AIUD-1#TRPBF pinout, LTC3851AIUD-1#TRPBF application, or LTC3851AIUD-1#TRPBF equivalent, key selection criteria include its 16-pin 3mm × 3mm QFN package, RSENSE/DCR current sensing flexibility, selectable light-load modes (Burst/Pulse-Skip/CCM), 99% duty cycle capability, and integrated 5V INTVCC regulator with 50mA peak drive.

Technical Context

The LTC3851AIUD-1#TRPBF implements a constant-frequency current-mode control architecture with slope compensation, where peak inductor current is set by the ITH voltage and regulated via an error amplifier comparing VFB to a 0.8V reference. Its anti-shoot-through logic prevents simultaneous conduction of top and bottom MOSFETs, while the dropout detector forces periodic top-FET off-time to recharge the bootstrap capacitor during near-100% duty operation.

Phase-locking is achieved via the MODE/PLLIN pin accepting external clocks (250–750kHz), with FREQ/PLLFLTR serving as PLL loop filter node; the improved PLL over LTC3851-1 enables tighter jitter control and faster lock acquisition. Output tracking and soft-start are implemented through TK/SS pin voltage ramping (1µA internal current), enabling coincident or ratiometric sequencing with master supplies.

Key Specifications

Pinout & Package

Package: 16-lead (3mm × 3mm) plastic QFN with exposed thermal pad (Pin 17 = GND), rated for –40°C to 125°C operating junction temperature (θJA = 68°C/W).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC3851AIMSE-1#TRPBF, the LTC3851AIUD-1#TRPBF offers superior thermal performance via its QFN exposed pad, enabling higher continuous current in compact layouts; versus MP2918GL-Z, it provides greater design flexibility through external MOSFET selection, programmable frequency, and advanced current sensing - critical for high-efficiency, high-reliability systems.

Availability

LTC3851AIUD-1#TRPBF is available at Aetrix Electronics and suitable for telecom intermediate bus converters, industrial 24V point-of-load supplies, and automotive infotainment power systems requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for LTC3851AIUD-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, Inc. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving precision instrumentation, industrial automation, and communications markets.

The LTC3851A family is designed for high-efficiency, high-reliability synchronous buck controller applications demanding wide input range, precise regulation, flexible light-load operation, and robust protection - targeting telecom, industrial, and automotive power systems.

FAQ

What is the maximum supported switching frequency for the LTC3851AIUD-1#TRPBF?

The LTC3851AIUD-1#TRPBF supports a phase-lockable switching frequency range of 250kHz to 750kHz. The upper limit of 750kHz is achieved with a 36kΩ resistor on the FREQ/PLLFLTR pin and is confirmed across the full –40°C to 125°C operating temperature range. This high-frequency capability enables smaller inductors and output capacitors in space-constrained designs while maintaining high efficiency.

Does the LTC3851AIUD-1#TRPBF support both RSENSE and DCR current sensing?

Yes, the LTC3851AIUD-1#TRPBF supports both RSENSE and DCR current sensing methods. SENSE+ and SENSE– pins accept either a discrete current-sense resistor or a DCR-based network across the inductor. This flexibility allows designers to optimize for accuracy (RSENSE) or efficiency/cost (DCR), with current foldback limiting active in both configurations to protect MOSFETs during short-circuit events.

How does the PGOOD function operate on the LTC3851AIUD-1#TRPBF?

The PGOOD pin on the LTC3851AIUD-1#TRPBF is an open-drain output that pulls low when VFB deviates more than ±10% from the 0.8V reference, during soft-start/tracking, or when RUN is low. It remains asserted low for 17µs after VFB exits the window (power-bad mask). Once VFB stabilizes within tolerance, PGOOD goes high-impedance and requires an external pull-up resistor to a voltage ≤6V to signal "power good" to system logic.

What is the purpose of the TK/SS pin on the LTC3851AIUD-1#TRPBF?

The TK/SS pin on the LTC3851AIUD-1#TRPBF serves dual functions: soft-start and supply tracking. An internal 1µA current charges an external capacitor to ramp VOUT smoothly from zero, preventing inrush current. Alternatively, connecting a resistor divider from a master supply to TK/SS enables coincident or ratiometric start-up sequencing - critical for multi-rail systems like SoCs where voltage ordering prevents latch-up or damage.

Can the LTC3851AIUD-1#TRPBF be synchronized to an external clock?

Yes, the LTC3851AIUD-1#TRPBF can be synchronized to an external clock applied to the MODE/PLLIN pin. When driven with a 250kHz–750kHz square wave, the internal PLL locks to the external source, forcing continuous conduction mode and eliminating beat frequencies. A series RC network on FREQ/PLLFLTR acts as the PLL loop filter, ensuring stable lock and low jitter - essential for EMI-sensitive multi-phase or dense PCB layouts.