Analog Devices Inc. LT3971EDD-5#PBF

Overview

LT3971EDD-5#PBF from Analog Devices (formerly Linear Technology) is a fixed 5V, 1.2A monolithic buck switching regulator in a 10-lead 3mm × 3mm DFN package with exposed pad. It operates from 4.3V to 38V input, delivers ultralow 2.8µA quiescent current in Burst Mode, maintains <15mV_P-P output ripple, and integrates a 0.33Ω switch, boost Schottky diode, and power good flag - ideal for automotive battery regulation and portable industrial supplies.

For engineers reviewing the LT3971EDD-5#PBF datasheet, LT3971EDD-5#PBF pinout, LT3971EDD-5#PBF application, or LT3971EDD-5#PBF equivalent, key selection criteria include its fixed 5V output accuracy (±1.5% over temperature), 200kHz–2MHz adjustable frequency via RT resistor, 1.01V enable threshold with 30mV hysteresis, and thermal performance enabled by the soldered exposed GND pad.

Technical Context

The LT3971EDD-5#PBF implements constant-frequency current-mode control with internal compensation, enabling fast transient response and stable loop behavior across wide input/output conditions. Its architecture integrates a bipolar NPN power switch driven by a BOOST pin voltage higher than VIN, supported by an on-die Schottky diode for bootstrapping.

Burst Mode operation reduces no-load supply current to 2.8µA while maintaining regulated 5V output and sub-15mV ripple; frequency foldback during startup and overload limits peak inductor current. The PG pin asserts open-drain high when VOUT reaches 91% of nominal 5V, validated only when VIN > 4.3V and EN is active.

Key Specifications

Pinout & Package

LT3971EDD-5#PBF uses a thermally enhanced 10-lead (3mm × 3mm) plastic DFN package with exposed GND pad (Pin 11), requiring PCB soldering for thermal and electrical integrity. 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 LMR36520RNXR and TPS6286518VRGTR, the LT3971EDD-5#PBF uniquely combines 38V tolerance, integrated boost diode, power good flag, and 2.8µA IQ in a thermally robust DFN - making it irreplaceable in automotive and wide-input industrial designs where reliability under voltage stress is non-negotiable.

Availability

LT3971EDD-5#PBF is available at Aetrix Electronics and suitable for automotive battery regulation, portable industrial sensors, and industrial PLC I/O modules requiring stable component supply across extended temperature and voltage ranges.

Supply support for LT3971EDD-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 full product support, manufacturing, and documentation for the LT3971 family.

The LT3971 series was designed specifically for high-reliability, wide-input DC/DC conversion in automotive, industrial, and medical applications where ultralow quiescent current and robust fault tolerance are mandatory.

FAQ

What is the guaranteed output voltage accuracy of the LT3971EDD-5#PBF over temperature?

The LT3971EDD-5#PBF guarantees 5.00V output within ±1.5% over the full –40°C to 125°C junction temperature range, as confirmed by electrical characterization data in the datasheet (page 3, "LT3971-5 Output Voltage" table). This accuracy is achieved using a factory-trimmed internal 10MΩ feedback divider, eliminating external resistor tolerance errors that affect adjustable regulators.

Can the LT3971EDD-5#PBF operate with input voltages below 4.3V?

No - the LT3971EDD-5#PBF requires a minimum input voltage of 4.3V to maintain regulated 5V output and proper internal circuit operation. Below this threshold, regulation fails and the device may not start or sustain output. The datasheet specifies 4.3V as the minimum for accurate FB regulation and confirms 5.0V as the practical start-up voltage for the 5V variant in typical applications.

How does the power good (PG) flag behave during input undervoltage or shutdown?

The PG pin remains low when VIN falls below 4.3V or when EN is pulled low, as power good validation requires both sufficient input voltage and active enable state. During normal operation, PG goes high only when VOUT reaches ≥4.55V (91% of 5V); it asserts low again if VOUT drops below 4.475V (91% minus 1.3% hysteresis), providing clean sequencing for downstream logic in the LT3971EDD-5#PBF system.

Is soft-start mandatory for the LT3971EDD-5#PBF, and what happens if the SS pin is left floating?

Soft-start is optional: floating the SS pin disables the feature, causing immediate full-current startup. However, this risks inrush current exceeding 2.4A switch limit and potential output overshoot. For reliable operation, a 1nF–10nF capacitor from SS to GND is recommended to ramp peak current over ~1–5ms - a design choice explicitly validated in LT3971EDD-5#PBF typical applications and block diagrams.

Does the LT3971EDD-5#PBF require an external catch diode, and what are the key selection criteria?

Yes - the LT3971EDD-5#PBF requires an external Schottky catch diode connected between SW and VOUT. Key criteria include ≤0.5V forward voltage at 1.2A, <1µA reverse leakage at 25°C (to preserve 2.8µA IQ), and adequate thermal derating for 125°C ambient. Diodes like DFLS2100 (cited in datasheet Figure G22) meet these specs and are validated in LT3971EDD-5#PBF reference layouts.