Analog Devices Inc. LT1506IR-3.3#PBF

Overview

LT1506IR-3.3#PBF from Analog Devices (formerly Linear Technology) is a fixed 3.3V, 4.5A monolithic buck switching regulator in SO-8 package with 500kHz current-mode operation, 0.07Ω switch on-resistance, and integrated cycle-by-cycle current limiting. It operates from 4V to 15V input and delivers stable 3.3V output for portable computing power rails.

For engineers reviewing the LT1506IR-3.3#PBF datasheet, LT1506IR-3.3#PBF pinout, LT1506IR-3.3#PBF application, or LT1506IR-3.3#PBF equivalent, key selection criteria include minimum input voltage (4.0V), shutdown current (20µA), SENSE pin accuracy (±1.5% over temperature), thermal shutdown, and compatibility with standard surface-mount inductors down to 1.8µH.

Technical Context

The LT1506IR-3.3#PBF implements constant-frequency current-mode control using an internal 500kHz oscillator and peak-current sensing via the SENSE pin. Its bipolar NPN power switch is saturated via BOOST pin drive, enabling low conduction loss (0.07Ω typical) without external gate drivers.

It features dual-threshold shutdown (0.37V start-up / 2.38V UVLO lockout), frequency foldback below 1V SENSE, and slope-compensated current limiting that degrades gracefully from 4.5A at ≤50% duty cycle to 3.7A at 80% duty cycle - all implemented without external compensation components beyond VC pin.

Key Specifications

Pinout & Package

LT1506IR-3.3#PBF is housed in an 8-lead plastic SO package (SO-8) with fused GND pin attached to internal tab for enhanced thermal performance (θ_JA = 80°C/W). GND pin must be soldered to large copper area for reliable thermal dissipation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC3605EDE-3.3#PBF and TPS54331DR, the LT1506IR-3.3#PBF delivers higher output current (4.5A vs 4A/3A) and superior efficiency at medium loads due to its BOOST-driven saturated switch, but operates at lower frequency and requires careful BOOST capacitor placement.

Availability

LT1506IR-3.3#PBF is available at Aetrix Electronics and suitable for portable computers, battery-powered instrumentation, and distributed power systems requiring stable component supply, long-lifecycle support, and proven reliability in industrial temperature range (–40°C to 125°C).

Supply support for LT1506IR-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 technical and manufacturing continuity for the LT® product family. Linear pioneered high-performance analog and power management ICs with emphasis on precision, efficiency, and ruggedness.

The LT1506IR-3.3#PBF belongs to Linear's monolithic buck regulator product line, designed specifically for low-input-voltage, high-current DC/DC conversion in space- and thermally constrained environments where simplicity and reliability are critical.

FAQ

What is the minimum input voltage required for stable operation of the LT1506IR-3.3#PBF?

The LT1506IR-3.3#PBF guarantees stable regulation down to 4.0V input across temperature. Below this, internal bias rails may collapse, causing loss of regulation or shutdown. At 3.3V output and 4A load, practical minimum VIN is ~4.3V to maintain >90% duty cycle margin - verified in Typical Performance Characteristics Figure G12.

How does the BOOST pin function in the LT1506IR-3.3#PBF, and what external components are required?

The BOOST pin in the LT1506IR-3.3#PBF supplies elevated drive voltage to the internal NPN switch base, enabling saturation and minimizing V_CE(sat). It requires an external flying capacitor (e.g., 10nF ceramic) and Schottky diode (e.g., MBRS330T3) from VIN to BOOST. Without proper BOOST bias, switch resistance rises to ~0.13Ω, degrading efficiency by ~5%.

Can the LT1506IR-3.3#PBF be synchronized to an external clock, and if not, what are the alternatives?

No - the LT1506IR-3.3#PBF uses the SHDN pin; it does not include SYNC functionality. For synchronization, select the LT1506IR-3.3#PBF-SYNC variant (order code LT1506IR-3.3 SYNC), which replaces SHDN with SYNC and supports 580kHz–1MHz external clock locking. Pinout and thermal design differ, so PCB layout is not interchangeable.

What is the purpose of the SENSE pin on the LT1506IR-3.3#PBF, and how does it differ from the FB pin?

The SENSE pin on the LT1506IR-3.3#PBF replaces the FB pin used on adjustable versions. It connects directly to the 3.3V output and internally references 3.3V ±1.5%. Unlike FB, it has no external resistor divider - eliminating divider error and bias current effects. Its Thevenin impedance must remain ≤4kΩ to ensure proper foldback behavior during faults.

Does the LT1506IR-3.3#PBF include thermal shutdown, and at what junction temperature does it activate?

Yes, the LT1506IR-3.3#PBF includes thermal shutdown that activates at approximately 165°C junction temperature. This is distinct from the 125°C maximum operating junction temperature (T_JMAX). Once tripped, the device halts switching and remains latched off until junction temperature falls below ~150°C, preventing thermal runaway under sustained overload or inadequate heatsinking.