Analog Devices Inc. LT3971IDD-3.3#PBF

Overview

LT3971IDD-3.3#PBF from Analog Devices (formerly Linear Technology) is a fixed-output 3.3V, 1.2A monolithic buck switching regulator in a thermally enhanced 10-lead (3mm × 3mm) DFN package. It operates from 4.3V to 38V input, delivers ultralow 2.8µA quiescent current in regulation, maintains <15mV_P-P output ripple via low-ripple Burst Mode®, and integrates power switch, boost Schottky diode, and internal compensation - designed for automotive battery regulation and portable industrial power supplies.

For engineers reviewing the LT3971IDD-3.3#PBF datasheet, LT3971IDD-3.3#PBF pinout, LT3971IDD-3.3#PBF application, or LT3971IDD-3.3#PBF equivalent, key selection criteria include its fixed 3.3V output accuracy (±1.5% over temperature), 700nA shutdown current, power-good flag with 9% hysteresis, soft-start control via SS pin, and synchronization capability up to 2MHz.

Technical Context

The LT3971IDD-3.3#PBF implements constant-frequency current-mode control with internal 10MΩ feedback divider setting V_OUT = 3.3V (V_FB = 1.19V). Its oscillator supports 200kHz–2MHz operation via RT resistor or external SYNC signal, and includes frequency foldback during startup/overload to limit inrush current.

Burst Mode® operation reduces no-load supply current to 2.8µA while maintaining output regulation and sub-15mV ripple; enabling high efficiency down to µA-level loads. The integrated bipolar NPN switch (R_DS(on) ≈ 330mΩ) is driven by a charge-pump boosted gate voltage (via BOOST/BD pins), requiring an external Schottky diode connected between BD and V_OUT.

Key Specifications

Pinout & Package

LT3971IDD-3.3#PBF uses a 10-lead (3mm × 3mm) plastic DFN package with exposed pad (Pin 11) soldered to PCB for thermal management (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 LT8609SIS8E#TRPBF, LT3971IDD-3.3#PBF offers superior input voltage range (4.3V–38V vs. 3.5V–42V with tighter derating) and integrated BD/BOOST functionality for simpler layout, while TPS54202HDDCR trades off ruggedness for lower BOM count and smaller solution size in mid-range industrial applications.

Availability

LT3971IDD-3.3#PBF is available at Aetrix Electronics and suitable for automotive battery regulation, portable industrial sensors, and railway signaling equipment requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LT3971IDD-3.3#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, documentation, and manufacturing continuity for the LT3971 family.

The LT3971 product line delivers high-efficiency, ultralow-I_Q buck regulators targeting always-on automotive, industrial, and IoT applications where battery longevity and wide-input operation are critical.

FAQ

What is the guaranteed output voltage accuracy of the LT3971IDD-3.3#PBF over temperature?

The LT3971IDD-3.3#PBF guarantees 3.3V output voltage within ±1.5% over the full –40°C to 125°C junction temperature range, as confirmed by electrical characteristics tables specifying 3.25V to 3.35V min/max limits at temperature extremes. This accuracy derives from its trimmed internal 10MΩ feedback divider and 1.19V reference, eliminating external resistor drift errors inherent in adjustable variants.

Does the LT3971IDD-3.3#PBF require an external Schottky diode, and why?

Yes, the LT3971IDD-3.3#PBF requires an external Schottky diode connected between the BD pin and VOUT. The BD pin serves as the anode connection for the charge-pump boost circuit that drives the BOOST pin, enabling full saturation of the internal bipolar NPN switch. Without this diode, the BOOST voltage cannot be generated, preventing proper switch operation and causing failure to regulate.

How does the LT3971IDD-3.3#PBF achieve 2.8µA quiescent current while maintaining regulation?

The LT3971IDD-3.3#PBF achieves 2.8µA quiescent current using low-ripple Burst Mode® operation: it delivers discrete current pulses to the output capacitor during light loads, then enters deep sleep between bursts where most internal circuitry is disabled. During sleep, only essential bias currents remain active, reducing total input current to 2.8µA while holding VOUT within regulation tolerance and limiting ripple to <15mV_P-P.

Can the LT3971IDD-3.3#PBF be synchronized to an external clock, and what is the impact on quiescent current?

Yes, the LT3971IDD-3.3#PBF can be synchronized to an external clock applied to the SYNC pin (250kHz–2MHz range). However, synchronization forces pulse-skipping instead of Burst Mode® during light loads, increasing quiescent current from 2.8µA to 1.5mA. For ultralow-power applications, SYNC must be grounded to enable true Burst Mode® operation.

What thermal considerations apply to the LT3971IDD-3.3#PBF in a 1.2A application?

In a 1.2A application, the LT3971IDD-3.3#PBF requires adequate PCB copper area connected to its exposed GND pad (Pin 11) to maintain θ_JA ≤ 45°C/W. With 2cm² of 2oz copper on inner layers, junction temperature rise remains below 50°C at 25°C ambient. Derating is required above 85°C ambient; maximum continuous output current drops to ~0.9A at 100°C ambient per thermal curves in the datasheet.