Analog Devices Inc. LT1506IR-3.3#TRPBF

Overview

LT1506IR-3.3#TRPBF from Analog Devices (formerly Linear Technology) is a 4.5A, 500kHz monolithic step-down switching regulator with fixed 3.3V output, optimized for low-input-voltage applications (4V–15V). It integrates a saturated NPN power switch (0.07Ω on-resistance), current-mode control, cycle-by-cycle current limiting, and thermal shutdown. It is used in portable computers and battery-powered systems requiring compact, efficient DC/DC conversion.

For engineers reviewing the LT1506IR-3.3#TRPBF datasheet, LT1506IR-3.3#TRPBF pinout, LT1506IR-3.3#TRPBF application, or LT1506IR-3.3#TRPBF equivalent, key selection criteria include input voltage range (4V–15V), fixed 3.3V output tolerance (±1.5%), shutdown current (≤50µA), SENSE pin interface, and SO-8 fused-lead package compatibility with surface-mount PCB layouts.

Technical Context

The LT1506IR-3.3#TRPBF implements constant-frequency current-mode control using an internal 500kHz oscillator and peak-current sensing via the SENSE pin. Its bipolar NPN switch is driven by a BOOST pin to achieve saturation, reducing conduction loss and enabling >89% efficiency at full load with 5V input.

It features dual-threshold shutdown (0.37V start-up / 2.38V lockout), frequency foldback below 1V SENSE voltage, and slope compensation to prevent subharmonic oscillation at duty cycles above 50%. The SENSE pin replaces FB and connects directly to the 3.3V output for regulation.

Key Specifications

Pinout & Package

The LT1506IR-3.3#TRPBF is housed in an 8-lead plastic SO package with fused GND pin (θ_JA = 80°C/W). The GND tab is internally connected to the die substrate and must be soldered to a large copper area for thermal performance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC3605EDE-3.3#TRPBF and TPS54331DR, the LT1506IR-3.3#TRPBF offers higher current (4.5A), lower minimum input (4.0V), and fixed 3.3V output without external resistors - making it optimal for cost-sensitive, high-current, low-VIN applications where ±1.5% accuracy is acceptable.

Availability

LT1506IR-3.3#TRPBF is available at Aetrix Electronics and suitable for portable computers, battery-powered systems, and distributed power applications requiring stable component supply, long-term lifecycle support, and guaranteed traceable sourcing.

Supply support for LT1506IR-3.3#TRPBF 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) designs high-performance analog, mixed-signal, and power management ICs for precision, reliability, and ruggedness across industrial, automotive, and communications markets.

The LT1506IR-3.3#TRPBF belongs to Linear's legacy monolithic buck regulator family, engineered specifically for low-input-voltage, high-current DC/DC conversion in space-constrained portable and battery-operated systems.

FAQ

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

The LT1506IR-3.3#TRPBF guarantees operation down to 4.0V input, with typical minimum validated at 4.3V for full 4.5A load and 3.3V output. Below 4.0V, internal bias lines may de-regulate, causing oscillator frequency drift or loss of regulation. This limit is defined by internal reference stability-not absolute failure-and depends on output load and ambient temperature.

How does the SENSE pin function differ from the FB pin in the LT1506IR-3.3#TRPBF?

In the LT1506IR-3.3#TRPBF, the SENSE pin replaces the FB pin and connects directly to the 3.3V output to close the regulation loop. Unlike the adjustable FB pin (which expects 2.42V), SENSE monitors actual output voltage and triggers internal error amplification to maintain 3.3V ±1.5%. No external resistor divider is needed, simplifying layout and improving accuracy.

Can the LT1506IR-3.3#TRPBF be synchronized to an external clock?

No - the LT1506IR-3.3#TRPBF does not support synchronization. Only variants with "-SYNC" in the part number (e.g., LT1506IR-3.3#TRPBF-SYNC) replace the SHDN pin with a SYNC pin. The standard LT1506IR-3.3#TRPBF retains SHDN functionality and lacks internal circuitry for external clock injection or frequency locking.

What is the purpose of the BOOST pin on the LT1506IR-3.3#TRPBF, and how is it implemented?

The BOOST pin on the LT1506IR-3.3#TRPBF supplies elevated drive voltage to the internal NPN power switch base, enabling saturation and reducing on-resistance to 0.07Ω. It is implemented using an external bootstrap capacitor (e.g., 10nF ceramic) and Schottky diode (e.g., MBRS330T3) connected between VIN and BOOST. Minimum BOOST voltage is 2.3V above VIN to ensure full saturation under 4.5A load.

Does the LT1506IR-3.3#TRPBF include thermal protection, and how does it behave?

Yes - the LT1506IR-3.3#TRPBF includes thermal shutdown that activates at junction temperature ≥165°C. When triggered, the device halts switching, reduces supply current to ~5mA, and holds shutdown until junction temperature falls by ~15°C (thermal hysteresis). Recovery is automatic and does not require cycling SHDN. This protects the IC during sustained overload, poor PCB heatsinking, or high ambient conditions.