Analog Devices Inc. LT3991EMSE-5#TRPBF

Overview

LT3991EMSE-5#TRPBF from Analog Devices (formerly Linear Technology) is a fixed 5V, 1.2A monolithic step-down switching regulator with ultralow 2.8µA quiescent current in regulation, 4.3V–55V input range, and internal 0.44Ω NPN switch. It delivers stable 5V output for automotive battery-powered systems requiring long standby life and high efficiency at light loads.

For engineers reviewing the LT3991EMSE-5#TRPBF datasheet, LT3991EMSE-5#TRPBF pinout, LT3991EMSE-5#TRPBF application, or LT3991EMSE-5#TRPBF equivalent, this page provides verified package mapping (10-pin MSOP), confirmed pin functions (EN, PG, SYNC, SS, RT, BD, BOOST, SW, VIN, VOUT), fixed 5V output accuracy (±1.4% over –40°C to 125°C), and validated alternatives for automotive and industrial DC/DC conversion.

Technical Context

The LT3991EMSE-5#TRPBF implements constant-frequency current-mode control with internal compensation, enabling fast transient response and stable loop behavior without external compensation components. Its bipolar NPN switch architecture-driven via BOOST pin with integrated Schottky diode-supports high-efficiency saturation down to 4.3V input.

Burst Mode® operation reduces no-load input current to 2.8µA while maintaining output ripple below 15mV_P-P; frequency foldback during startup and overload protects against excessive peak currents. The power good (PG) flag asserts when VOUT reaches 91% of 5V, and EN pin features 1.01V rising threshold with 30mV hysteresis.

Key Specifications

Pinout & Package

LT3991EMSE-5#TRPBF is housed in a thermally enhanced 10-lead plastic MSOP package (3mm × 3mm footprint, exposed pad) with θ_JA = 45°C/W and θ_JC = 10°C/W. The exposed pad (Pin 11) must be soldered to PCB ground for optimal thermal and electrical performance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LT3991EMSE-5#TRPBF, LT8609SIV#TRPBF offers higher current and slightly lower IQ but demands external bootstrap design, while TPS54332DDAR lacks critical automotive features like PG flag, Burst Mode, and 55V tolerance-making LT3991EMSE-5#TRPBF uniquely suited for harsh-environment 5V regulation.

Availability

LT3991EMSE-5#TRPBF is available at Aetrix Electronics and suitable for automotive battery regulation, industrial sensor power supplies, portable medical devices, and smart building controllers requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LT3991EMSE-5#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 full product support, qualification, and manufacturing continuity for all LT® parts. Linear Technology pioneered high-performance analog ICs for demanding power and signal conditioning applications.

The LT3991 family was designed specifically for ultralow-power, wide-input-voltage DC/DC conversion in automotive, industrial, and portable equipment-emphasizing quiescent current, thermal robustness, and functional integration (e.g., internal boost path, PG flag, soft-start).

FAQ

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

The LT3991EMSE-5#TRPBF delivers 5.00V with ±1.4% accuracy across the full –40°C to 125°C junction temperature range, as specified in the Electrical Characteristics table. This tight tolerance is achieved via laser-trimmed internal feedback resistors and a stable 1.19V reference, eliminating drift-related calibration in automotive and industrial deployments where the LT3991EMSE-5#TRPBF operates continuously under thermal stress.

Does the LT3991EMSE-5#TRPBF require an external feedback resistor network?

No-the LT3991EMSE-5#TRPBF integrates a precision 10MΩ internal feedback divider that fixes the output to 5.00V, removing the need for external resistors. Unlike the adjustable LT3991 variant (which uses the FB pin), this part routes regulation sensing directly to the VOUT pin (Pin 6), simplifying layout and improving accuracy by avoiding resistor tolerance and PCB leakage effects. This design choice makes the LT3991EMSE-5#TRPBF ideal for cost-sensitive, high-volume applications where the LT3991EMSE-5#TRPBF's fixed 5V output meets system requirements.

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

The LT3991EMSE-5#TRPBF achieves 2.8µA quiescent current through low-ripple Burst Mode® operation: during light loads, it delivers discrete energy pulses to the output capacitor and enters deep sleep between bursts, shutting down oscillator, error amplifier, and gate drivers. This architecture-combined with optimized bipolar NPN switch biasing and leakage-minimized internal circuitry-ensures just 2.8µA is drawn from VIN while maintaining regulation. In contrast, the LT3991EMSE-5#TRPBF draws only 700nA in full shutdown (EN = low), making it suitable for battery-backed systems where the LT3991EMSE-5#TRPBF must preserve charge over years.

Can the LT3991EMSE-5#TRPBF synchronize to an external clock?

Yes-the LT3991EMSE-5#TRPBF supports external synchronization via the SYNC pin (Pin 10), accepting clocks from 250kHz to 2MHz. When synchronized, the LT3991EMSE-5#TRPBF switches to pulse-skipping mode at light loads instead of Burst Mode, increasing quiescent current to ~1.5mA but enabling EMI reduction through fixed-frequency operation. For lowest IQ, ground SYNC; for EMI-sensitive applications, drive SYNC with a clean system clock-ensuring the LT3991EMSE-5#TRPBF remains aligned with noise-reduction timing constraints.

What thermal considerations apply to the LT3991EMSE-5#TRPBF in a 10-pin MSOP package?

The LT3991EMSE-5#TRPBF's 10-pin MSOP package features an exposed thermal pad (Pin 11) that must be soldered to a minimum 100mm² copper pour tied to GND for effective heat dissipation. With θ_JA = 45°C/W and θ_JC = 10°C/W, the LT3991EMSE-5#TRPBF sustains 1.2A output at 70°C ambient without derating-provided the PCB layout follows Linear Technology's recommended thermal land pattern. Failure to solder the exposed pad increases junction temperature by >30°C, risking thermal shutdown or accelerated aging of the LT3991EMSE-5#TRPBF.