Analog Devices Inc. LT3973EDD-3.3#PBF

Overview

LT3973EDD-3.3#PBF from Analog Devices (formerly Linear Technology) is a 42V, 750mA monolithic step-down regulator with fixed 3.3V output, integrated boost and catch diodes, and 2.5µA quiescent current. It operates from 4.2V to 42V input, maintains low ripple Burst Mode operation (<10mV_P-P), and delivers automotive-grade performance with 530mV minimum dropout voltage during cold-crank conditions.

For engineers reviewing the LT3973EDD-3.3#PBF datasheet, LT3973EDD-3.3#PBF pinout, LT3973EDD-3.3#PBF application, or LT3973EDD-3.3#PBF equivalent, key selection considerations include its fixed 3.3V output accuracy (±1.2% over temperature), thermally enhanced 10-lead 3mm × 3mm DFN package, programmable UVLO, and power-good flag for system sequencing in battery-powered and industrial power supplies.

Technical Context

The LT3973EDD-3.3#PBF implements constant-frequency current-mode control with adjustable switching frequency (200kHz–2.2MHz via RT pin), enabling optimization of efficiency vs. size trade-offs. Its internal bipolar NPN switch and integrated Schottky diodes eliminate external components while supporting high duty-cycle operation up to ~97.5% via boost capacitor charge management.

It features dual current limiting-switch peak limit (1.65A typ.) and catch diode valley limit (1.15A typ.)-for robust short-circuit protection, plus thermal shutdown and accurate undervoltage lockout (1.19V rising threshold, 45mV hysteresis). The power-good flag activates when VOUT reaches 90% of regulation, valid only when VIN > 4.2V and EN/UVLO is high.

Key Specifications

Pinout & Package

LT3973EDD-3.3#PBF uses a thermally enhanced 10-lead (3mm × 3mm) plastic DFN package with exposed pad (Pin 11) soldered to PCB for optimal thermal performance (θ_JA = 40°C/W).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar step-down regulator applications.

Compared with LTC3630EMSE-3.3#PBF, LT3973EDD-3.3#PBF offers lower quiescent current and BD-bias capability for improved efficiency; compared with TPS54331DR, it provides integrated diodes and tighter output tolerance but lower max current-making it optimal for space-constrained, low-I_Q 3.3V systems.

Availability

LT3973EDD-3.3#PBF is available at Aetrix Electronics and suitable for automotive body electronics, industrial IoT sensor nodes, portable medical diagnostics, and factory automation I/O modules requiring stable component supply across extended temperature and long-lifecycle programs.

Supply support for LT3973EDD-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 its legacy of high-performance power management ICs with rigorous automotive and industrial qualification.

The LT3973 product line was designed specifically for demanding 42V-input environments-such as automotive, industrial, and avionics-where ultralow quiescent current, integrated diodes, and robust dropout performance are essential.

FAQ

What is the guaranteed output voltage accuracy of the LT3973EDD-3.3#PBF over temperature?

The LT3973EDD-3.3#PBF guarantees 3.3V output within ±1.2% over its full –40°C to 125°C junction temperature range, as specified in the Electrical Characteristics table (VOUT min/max = 3.26V/3.34V at –40°C to 125°C). This accuracy is achieved using an internal trimmed feedback divider and is independent of external resistor tolerances since no external resistors are needed for the fixed 3.3V version.

Can the LT3973EDD-3.3#PBF operate with input voltages below 4.2V?

Yes-the LT3973EDD-3.3#PBF begins switching at ~3V input, but regulation is not guaranteed below 4.2V. Below this voltage, the internal reference degrades and output voltage falls proportionally. For reliable 3.3V regulation, VIN must remain ≥4.2V; the device's 530mV dropout enforcement only applies when VIN > VOUT, and minimum input for regulation is governed by duty cycle limits and dropout voltage-not absolute startup capability.

How does the BD pin improve efficiency in the LT3973EDD-3.3#PBF?

The BD pin allows external bias (≥3.2V) to power the LT3973EDD-3.3#PBF's internal regulator instead of drawing from VIN. When tied to the regulated 3.3V output, this reduces input current draw and improves full-load efficiency by ~1–2%-particularly valuable in high-input-voltage applications (e.g., 24V or 36V input to 3.3V output) where VIN-to-VOUT conversion loss dominates.

Is the LT3973EDD-3.3#PBF pin-compatible with other LT3973 variants in the same package?

Yes-LT3973EDD-3.3#PBF shares identical pinout and package (10-lead 3mm × 3mm DFN) with LT3973EDD#PBF (adjustable), LT3973EDD-5#PBF (5V fixed), and all I/H-grade DFN variants. Pin functions are consistent; only the internal feedback network differs. However, the VOUT pin replaces FB on fixed-output versions, so external feedback networks must be omitted.

What thermal derating applies to the LT3973EDD-3.3#PBF at 125°C ambient?

At 125°C ambient, the LT3973EDD-3.3#PBF's maximum continuous output current is thermally limited-not by its 750mA rating, but by junction temperature. With θ_JA = 40°C/W and max T_J = 125°C, allowable power dissipation is (125°C – 125°C) / 40°C/W = 0W-meaning full 750mA load is only sustainable at lower ambient temperatures. Derating curves in the datasheet show ~450mA max at 100°C ambient with standard PCB copper.