Analog Devices Inc. LT3741IFE-1#PBF

Overview

LT3741IFE-1#PBF from Analog Devices (formerly Linear Technology) is a fixed-frequency synchronous step-down DC/DC controller optimized for high-accuracy constant-current and constant-voltage regulation up to 20A. It features average current-mode control, ±6% current regulation accuracy, ±1.5% voltage regulation accuracy, and supports input voltages from 6V to 36V with output voltage range up to (VIN – 2V). It is used in super-capacitor charging systems requiring precise current limiting and robust short-circuit protection.

For engineers reviewing the LT3741IFE-1#PBF datasheet, LT3741IFE-1#PBF pinout, LT3741IFE-1#PBF application, or LT3741IFE-1#PBF equivalent, key selection considerations include its dual CTRL pin thermal derating capability, 20-pin TSSOP package with exposed pad, 200kHz–1MHz programmable switching frequency, and ability to source/sink current - distinguishing it from the LT3741 (non-1) variant.

Technical Context

The LT3741IFE-1#PBF implements average current-mode control using internal gm amplifiers (475 µA/V for current loop, 850 µA/V for voltage loop) and a 2V buffered reference (VREF) with 1mA current limit. Its dual analog control inputs (CTRL1 and CTRL2) enable dynamic current limiting via external thermal feedback, with the lower of the two voltages (0–1.5V range) determining regulated output current.

It integrates high- and low-side gate drivers (HG/LG) with non-overlap timing (60–100 ns), programmable soft-start (11 µA charging current), overvoltage lockout at 1.5V FB threshold (13 µs shutdown), and thermal shutdown at 163°C (8°C hysteresis). The LT3741-1 variant disables sinking capability and removes zero-cross comparator circuitry present in LT3741.

Key Specifications

Pinout & Package

LT3741IFE-1#PBF uses a thermally enhanced 20-lead plastic TSSOP package with exposed pad (Pin 21 = GND), rated for –40°C to +125°C junction temperature (θJA = 38°C/W).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LT3741IFE-1#PBF, LTC3776 offers higher current capability but no native thermal foldback, while LM5118 supports wider input voltage and buck-boost operation but sacrifices current regulation accuracy and CTRL2 functionality.

Availability

LT3741IFE-1#PBF is available at Aetrix Electronics and suitable for super-capacitor charging, LED driver modules, and industrial battery formation systems requiring stable component supply and long-term manufacturability.

Supply support for LT3741IFE-1#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 semiconductors, formed through the acquisition of Linear Technology in 2017.

The LT3741 family was designed by Linear Technology specifically for high-accuracy, high-current constant-current/constant-voltage power conversion in demanding industrial and energy-storage applications.

FAQ

What is the key functional difference between LT3741IFE-1#PBF and LT3741IFE#PBF?

The LT3741IFE-1#PBF is the -1 variant, which disables current sinking capability and omits the zero-cross comparator found in the base LT3741. This simplifies design for unidirectional current applications (e.g., charging only) and improves noise immunity. The LT3741IFE#PBF retains bidirectional operation and is required for applications needing active current sinking, such as regenerative braking interfaces. Both share identical pinout, package, and core regulation accuracy.

Can LT3741IFE-1#PBF regulate output current down to 0A?

Yes - LT3741IFE-1#PBF supports true zero-current regulation. When CTRL1 and CTRL2 are both held at 0V, the internal current reference collapses, resulting in no gate drive activity and 0A output current. This is confirmed in the Electrical Characteristics table (CTRL1 control range: 0V to 1.5V) and Operation section, which states the regulated current is proportional to the lower of the two CTRL voltages, with 0V yielding 0mV sense voltage and thus zero inductor current.

What is the maximum supported sense resistor value for 20A output with LT3741IFE-1#PBF?

For 20A output, the maximum sense resistor value is 2.5 mΩ. This is derived from the typical sense voltage range of 0–51 mV (at CTRL1 = 1.5 V) and the formula IO = VCTRL1 / (30 × RS). At 1.5 V CTRL1, 51 mV appears across RS, so RS = 51 mV / 20 A = 2.55 mΩ. The datasheet's Typical Application schematic (TA01a) explicitly uses a 2.5 mΩ resistor for 20A operation, confirming this value as the practical maximum.

Does LT3741IFE-1#PBF require an external bootstrap diode?

Yes - LT3741IFE-1#PBF requires an external Schottky diode (e.g., 1N5819) from VCC_INT to CBOOT to charge the bootstrap capacitor during low-side conduction. This is mandatory per the PIN FUNCTIONS section: "An external Schottky diode is required from the VCC_INT pin to the CBOOT pin to charge the CBOOT capacitor when the switch-pin is near ground." Omitting it prevents high-side gate drive and causes immediate failure.

How does the CTRL2 pin provide thermal control in LT3741IFE-1#PBF?

The CTRL2 pin accepts an analog voltage (0–1.5V) that competes with CTRL1 to determine regulated current - the lower voltage wins. In thermal control, a thermistor-based voltage divider applies decreasing voltage to CTRL2 as temperature rises, automatically reducing regulated current before reaching thermal shutdown (163°C). This is documented in the PIN FUNCTIONS section ("Thermal control input used to reduce the regulated current level") and OPERATION section ("lower of the two analog voltages on CTRL1 and CTRL2 determines the regulated output current").