Analog Devices Inc. LT3971IDD-5#PBF

Overview

LT3971IDD-5#PBF from Analog Devices (formerly Linear Technology) is a fixed 5V, 1.2A monolithic buck switching regulator in a thermally enhanced 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 LT3971IDD-5#PBF datasheet, LT3971IDD-5#PBF pinout, LT3971IDD-5#PBF application, or LT3971IDD-5#PBF equivalent, key selection criteria include its fixed 5V output, 2.8µA no-load IQ, 38V max VIN tolerance, 1.2A continuous output, and integrated soft-start and PG signaling - all verified for –40°C to 125°C operation.

Technical Context

The LT3971IDD-5#PBF implements constant-frequency current-mode control with internal compensation, enabling fast transient response and stable loop behavior across wide load and line variations. Its architecture includes an internally trimmed 10MΩ feedback divider for precise 5V regulation (±1.5% over temperature), frequency programmability via RT pin (200kHz–2MHz), and synchronous Burst Mode operation that reduces input current to 1.7µA during sleep cycles while maintaining low ripple.

It features a bipolar NPN power switch driven by a BOOST pin voltage higher than VIN, requiring an external boost capacitor; a 1V enable threshold with 30mV hysteresis; and a power good comparator asserting when VOUT reaches 91% of nominal - all supported by thermal shutdown and current-limit protection.

Key Specifications

Pinout & Package

LT3971IDD-5#PBF uses a 10-lead (3mm × 3mm) plastic DFN package with exposed thermal pad (Pin 11 = GND), optimized for low θ_JA = 45°C/W and high power density in space-constrained designs.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LMR36520RNXR and TPS54202DRCT, the LT3971IDD-5#PBF uniquely combines fixed 5V output, 2.8µA IQ, 38V input, integrated PG, and boost diode - making it optimal for automotive and long-life battery systems where reliability and simplicity are critical.

Availability

LT3971IDD-5#PBF is available at Aetrix Electronics and suitable for automotive battery regulation, portable medical devices, industrial IoT sensor nodes, and factory automation I/O modules requiring stable component supply across extended temperature ranges.

Supply support for LT3971IDD-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 analog and power management ICs for demanding applications.

The LT3971 series was designed specifically for ultralow-quiescent-current step-down regulation in automotive, industrial, and battery-powered systems where efficiency at light loads and robustness across wide input voltages are essential.

FAQ

What is the guaranteed output voltage accuracy of the LT3971IDD-5#PBF over temperature?

The LT3971IDD-5#PBF guarantees a 5.0V output with ±1.5% tolerance over the full –40°C to 125°C junction temperature range, as confirmed by electrical characterization data in the datasheet. This accuracy is achieved using an internal 10MΩ feedback divider trimmed at wafer test - no external resistors are required, and the specification holds regardless of input voltage or load within rated limits.

Does the LT3971IDD-5#PBF require an external catch diode?

No, the LT3971IDD-5#PBF integrates a boost Schottky diode and does not require an external catch diode. The BD pin connects directly to the anode of the internal diode, which is tied to VOUT. However, an external Schottky diode is still required between SW and VOUT to complete the buck topology - the internal diode serves only the bootstrap function for the NPN switch driver.

How does the LT3971IDD-5#PBF achieve 2.8µA quiescent current?

The LT3971IDD-5#PBF achieves 2.8µA quiescent current through low-ripple Burst Mode operation: during light loads, it delivers discrete current pulses to the output capacitor and enters deep sleep between bursts, reducing circuit activity. In sleep mode, total input current drops to 1.7µA; the 2.8µA figure reflects average consumption including brief active periods - verified at 12V_IN→5V_OUT with no load.

Can the LT3971IDD-5#PBF be synchronized to an external clock?

Yes, the LT3971IDD-5#PBF can be synchronized to an external clock via the SYNC pin, which accepts frequencies from 250kHz to 2MHz. When synchronized, it operates in pulse-skipping mode at light loads instead of Burst Mode, increasing quiescent current to ~1.5mA. For ultralow IQ, SYNC must be grounded - this configures true low-ripple Burst Mode as specified for the LT3971IDD-5#PBF.

What thermal performance can be expected from the LT3971IDD-5#PBF in a standard PCB layout?

In a standard 4-layer PCB with 2oz copper and 1in² exposed GND copper connected to the exposed pad (Pin 11), the LT3971IDD-5#PBF achieves θ_JA ≈ 45°C/W. At 1.2A output and 12V_IN→5V_OUT, power dissipation is ~0.84W, resulting in ~38°C junction rise above ambient - well within the 125°C max junction rating. Thermal derating begins above 100°C ambient per datasheet curves.