Analog Devices Inc. LT3991EMSE-5#PBF

Overview

LT3991EMSE-5#PBF from Analog Devices (formerly Linear Technology) is a 55V, 1.2A monolithic step-down DC/DC regulator with fixed 5V output, ultralow 2.8µA quiescent current in regulation, and internal compensation. It integrates a 0.44Ω NPN switch, boost Schottky diode, soft-start, power good flag, and 200kHz–2MHz adjustable switching frequency. Used in automotive battery regulation and industrial supplies where low standby power and wide VIN are critical.

For engineers reviewing the LT3991EMSE-5#PBF datasheet, LT3991EMSE-5#PBF pinout, LT3991EMSE-5#PBF application, or LT3991EMSE-5#PBF equivalent, key selection factors include its 5V fixed output accuracy (±1.4% over temperature), 700nA shutdown current, Burst Mode ripple <15mV_P-P, 4.3V–55V input range, and MSOP-10 thermally enhanced package with exposed GND pad.

Technical Context

The LT3991EMSE-5#PBF employs constant-frequency current-mode control with internal slope compensation and an actively clamped VC node for stable loop dynamics and fast transient response. Its bipolar NPN switch is driven from either VIN or BOOST, enabling full saturation across input voltage range.

Burst Mode operation reduces no-load supply current to 2.8µA by gating the oscillator and disabling nonessential circuitry between energy pulses, while maintaining output regulation and keeping ripple below 15mV_P-P. Frequency foldback during startup and overload prevents excessive peak inductor current.

Key Specifications

Pinout & Package

LT3991EMSE-5#PBF is housed in a thermally enhanced 10-lead plastic MSOP package (3mm × 3mm footprint) with exposed GND pad (Pin 11) requiring PCB soldering for optimal thermal performance (θ_JA = 45°C/W, θ_JC = 10°C/W).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar fixed-output buck regulator applications.

Compared with LT3991EMSE-5#PBF, LT8609SIV-5#PBF offers higher output current and optional integrated inductor but lacks 55V input support; TPS63020DSJR provides buck-boost flexibility at the cost of 9× higher quiescent current and no power good output - making LT3991EMSE-5#PBF optimal for high-VIN, low-I_Q, and sequenced-system applications.

Availability

LT3991EMSE-5#PBF is available at Aetrix Electronics and suitable for automotive battery regulation, industrial sensor node power, and portable medical device supply requiring stable component supply, long-lifecycle availability, and AEC-Q200-aligned reliability.

Supply support for LT3991EMSE-5#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 its legacy of high-performance power management ICs with rigorous characterization and automotive-grade qualification.

The LT3991 product line delivers ultralow-quiescent-current buck regulators for always-on systems in automotive, industrial, and portable applications where battery longevity and wide-input operation are essential.

FAQ

What is the output voltage tolerance of the LT3991EMSE-5#PBF over temperature?

The LT3991EMSE-5#PBF delivers a fixed 5.00V output with ±1.4% total error over the full –40°C to 125°C junction temperature range, including initial accuracy, line regulation, and load regulation. This is achieved via laser-trimmed internal 10MΩ feedback resistors and a precision 1.19V reference, eliminating external resistor drift concerns in the LT3991EMSE-5#PBF design.

Can the LT3991EMSE-5#PBF operate from a 48V input while delivering 1.2A at 5V?

Yes, the LT3991EMSE-5#PBF supports 48V input and 1.2A output continuously when properly thermally managed. With its 0.44Ω switch, typical efficiency exceeds 88% at 48V→5V/1.2A (f_SW = 400kHz), and the MSOP-10 package's θ_JA = 45°C/W allows operation up to 85°C ambient with standard 2-layer PCB copper area. Derating applies above 100°C junction temperature.

How does the LT3991EMSE-5#PBF achieve 2.8µA quiescent current?

The LT3991EMSE-5#PBF achieves 2.8µA quiescent current using patented low-ripple Burst Mode operation: the controller shuts down all nonessential circuitry between discrete energy pulses, reducing supply current to 1.7µA in sleep state. The 2.8µA figure reflects average current during active regulation - including brief 1.5mA bursts needed to recharge the output capacitor while maintaining <15mV_P-P ripple in the LT3991EMSE-5#PBF.

Is the LT3991EMSE-5#PBF pin-compatible with other LT3991 variants like LT3991EMSE-3.3#PBF?

Yes, the LT3991EMSE-5#PBF shares identical MSOP-10 pinout, package dimensions, and thermal pad layout with LT3991EMSE-3.3#PBF and LT3991EMSE#PBF. Only the internal feedback divider differs - VOUT (Pin 6) is hardwired to 5.00V in LT3991EMSE-5#PBF versus 3.3V or adjustable mode - allowing direct PCB substitution where 5V output is required.

Does the LT3991EMSE-5#PBF require an external catch diode?

No, the LT3991EMSE-5#PBF integrates a Schottky boost diode on-die connected to the BD pin, eliminating the need for an external catch diode. The internal diode handles bootstrapping and provides reverse-blocking during switch off-time. An external Schottky is still required between SW and VOUT for the main power path - this is standard for NPN-based buck regulators like the LT3991EMSE-5#PBF.