Analog Devices Inc. LT3741IUF#PBF

Overview

LT3741IUF#PBF from Analog Devices (formerly Linear Technology) is a fixed-frequency, average current-mode synchronous step-down DC/DC controller designed to regulate output current up to 20A with ±6% accuracy and output voltage up to (VIN – 2V) with ±1.5% regulation accuracy. It supports sourcing and sinking current, features dual analog control inputs (CTRL1/CTRL2), and operates across 6V–36V input range - used in high-reliability constant-current power supplies for supercapacitor charging and industrial LED drivers.

For engineers reviewing the LT3741IUF#PBF datasheet, LT3741IUF#PBF pinout, LT3741IUF#PBF application, or LT3741IUF#PBF equivalent, key selection considerations include its bidirectional current capability, thermal derating via CTRL2, programmable switching frequency (200kHz–1MHz), integrated 2V reference, and precise overvoltage lockout at 1.5V on FB pin.

Technical Context

The LT3741IUF#PBF implements average current-mode control using an internal gm amplifier (475 µA/V) and common-mode lockout (0V to VIN–2V), enabling stable regulation independent of output voltage. Its dual-control architecture compares voltages on CTRL1 and CTRL2 pins to determine regulated current, with internal 1.5V clamping and 23mV overcurrent offset referenced to SENSE+–SENSE–.

It integrates a 5V internal regulator (VCC_INT), high-side (HG) and low-side (LG) gate drivers with matched non-overlap timing (60–100 ns), and supports external synchronization via SYNC pin. The RT pin sets frequency with 60 µA current limit, while EN/UVLO provides programmable hysteresis (130 mV) and full shutdown below 0.5V.

Key Specifications

Pinout & Package

LT3741IUF#PBF uses a thermally enhanced 20-lead (4mm × 4mm) plastic QFN package with exposed pad (Pin 21) soldered to PCB ground for thermal dissipation (θJA = 37°C/W). The package supports high-power density layouts and is RoHS-compliant with lead-free finish.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar constant-current step-down controller applications.

Compared with LTC3775EFE#PBF and LM5119PWPR, the LT3741IUF#PBF uniquely combines bidirectional current regulation, integrated thermal derating (CTRL2), and ±6% current accuracy in a single 20-pin QFN - making it optimal for supercap charging and programmable current-source designs where simplicity and functional integration are critical.

Availability

LT3741IUF#PBF is available at Aetrix Electronics and suitable for supercapacitor charging, industrial LED drivers, and high-reliability battery test equipment requiring stable component supply, extended temperature support (–40°C to +125°C), and RoHS-compliant packaging.

Supply support for LT3741IUF#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 (ADI) is a global leader in high-performance analog, mixed-signal, and digital signal processing technologies, serving industrial, automotive, communications, and healthcare markets.

The LT3741 product line was developed by Linear Technology (acquired by ADI in 2017) specifically for high-accuracy, high-current constant-current and constant-voltage DC/DC conversion - targeting applications demanding bidirectional energy flow and robust thermal management.

FAQ

What is the maximum output current supported by the LT3741IUF#PBF?

The LT3741IUF#PBF supports regulated output current up to 20A with ±6% accuracy. This is achieved using an external sense resistor (e.g., 2.5mΩ) and the CTRL1 pin voltage (up to 1.5V), which sets the average inductor current. Peak current capability depends on MOSFET selection, inductor saturation rating, and thermal design - but the controller's architecture is validated for continuous 20A operation in typical 4-layer PCB layouts with proper thermal vias.

Does the LT3741IUF#PBF support current sinking as well as sourcing?

Yes, the LT3741IUF#PBF supports both sourcing and sinking current - a defining feature distinguishing it from standard buck controllers. This bidirectional capability is enabled by its unique average current-mode topology and complementary high-side/low-side gate drivers (HG and LG). It is explicitly intended for applications like supercapacitor charging/discharging and regenerative load testing, unlike the LT3741-1 variant, which disables sinking.

How does the CTRL2 pin function in the LT3741IUF#PBF?

The CTRL2 pin in the LT3741IUF#PBF provides thermal derating control: the lower of the voltages on CTRL1 and CTRL2 determines the final regulated current. When a thermistor network pulls CTRL2 below CTRL1, the controller automatically reduces output current to prevent overheating. This analog feedback eliminates need for microcontroller intervention and enables seamless integration into thermally constrained industrial enclosures.

What is the purpose of the exposed pad (Pin 21) on the LT3741IUF#PBF QFN package?

The exposed pad (Pin 21) on the LT3741IUF#PBF is electrically and thermally connected to GND. It must be soldered to a PCB copper pour with multiple thermal vias to achieve the specified θJA of 37°C/W. This pad is critical for dissipating up to 2W of internal power during 20A operation and ensures reliable performance across the full –40°C to +125°C junction temperature range.

Can the LT3741IUF#PBF be synchronized to an external clock?

Yes, the LT3741IUF#PBF supports external clock synchronization via the SYNC pin. To avoid beat frequencies, the internal oscillator (set by the RT resistor) must operate at least 20% slower than the external SYNC signal frequency. The SYNC pin accepts TTL/CMOS-level clocks and should be grounded when unused. This feature enables EMI reduction in noise-sensitive systems such as medical or test equipment.