Analog Devices Inc. LT3651IUHE-4.2#TRPBF

Overview

LT3651IUHE-4.2#TRPBF from Analog Devices (formerly Linear Technology) is a monolithic 4A synchronous step-down Li-ion battery charger IC for single-cell applications, supporting 6.5V–32V input and delivering 4.2V ±0.5% float voltage with 0.5% accuracy, 7.5% charge current accuracy, and NTC-based temperature monitoring. It enables high-efficiency charging in automotive cradle chargers and industrial handheld instruments.

For engineers reviewing the LT3651IUHE-4.2#TRPBF datasheet, LT3651IUHE-4.2#TRPBF pinout, LT3651IUHE-4.2#TRPBF application, or LT3651IUHE-4.2#TRPBF equivalent, key selection criteria include its 4A programmable charge current, C/10 or timer-based termination, dynamic input current limiting via ILIM, thermal foldback protection, and 36-pin QFN package with exposed SW and GND pads for thermal management.

Technical Context

The LT3651IUHE-4.2#TRPBF implements average current mode control using dual error amplifiers: V-EA regulates battery voltage against a 4.2V internal reference, while C-EA compares scaled ITH to the SENSE–BAT voltage to enforce precise constant-current regulation. Its synchronous switcher uses bootstrapped high-side drive (BOOST pin) and integrated low-side MOSFETs.

Charge sequencing includes automatic preconditioning below 2.9V battery voltage (clamping ITH to 0.15V), CV transition at float voltage, C/10 detection at 0.1V ITH, and timer-based termination configurable up to 3 hours via TIMER pin capacitor. Fault handling integrates NTC voltage window detection (0.29V–1.36V), die temperature foldback, and open-collector FAULT/CHRG status outputs.

Key Specifications

Pinout & Package

LT3651IUHE-4.2#TRPBF is housed in a 5mm × 6mm 36-pin plastic QFN package with two exposed thermal pads: Pin 37 (GND) and Pin 38 (SW). Both must be soldered to PCB copper for electrical integrity and thermal dissipation. The package supports high-power operation with θJA = 43°C/W.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar Li-ion battery charger applications.

Compared with BQ24616RGER and MP2617GQZ, the LT3651IUHE-4.2#TRPBF delivers fully autonomous charging with hardware-enforced safety (NTC, precondition, timer, thermal foldback), eliminating MCU dependency while maintaining 4A capability in a monolithic 36-pin QFN - critical for robust industrial and automotive deployments.

Availability

LT3651IUHE-4.2#TRPBF is available at Aetrix Electronics and suitable for industrial handheld instruments, 12V to 24V automotive systems, and desktop cradle chargers requiring stable component supply, long-term lifecycle support, and guaranteed parametric performance across –40°C to +125°C.

Supply support for LT3651IUHE-4.2#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 and maintains its high-performance analog IC portfolio, emphasizing precision, reliability, and ruggedness for demanding industrial and automotive applications.

The LT3651 product line delivers monolithic, high-current Li-ion charging solutions optimized for wide-input industrial power supplies and harsh-environment battery systems - designed to replace discrete charger controllers with integrated safety and thermal management.

FAQ

What is the exact float voltage specification for LT3651IUHE-4.2#TRPBF?

The LT3651IUHE-4.2#TRPBF is factory trimmed to deliver a nominal 4.2V battery float voltage with ±0.02V (±0.5%) accuracy over the full –40°C to +125°C junction temperature range. This value is fixed for the -4.2 variant and differs from the -4.1 version's 4.1V setting. The specification is guaranteed by design and characterization per Linear Technology's datasheet Rev. D.

How does LT3651IUHE-4.2#TRPBF implement battery preconditioning?

The LT3651IUHE-4.2#TRPBF initiates preconditioning automatically when the BAT pin voltage falls below 2.9V. During this mode, it clamps the ITH voltage to 0.15V, reducing charge current to 15% of the programmed maximum. Preconditioning continues until VBAT exceeds 2.9V or times out after 22.5 minutes - triggering a bad battery fault if unresponsive. This prevents lithium plating on deeply discharged cells.

Can LT3651IUHE-4.2#TRPBF operate without an NTC thermistor?

Yes - the NTC pin (Pin 1) is optional. If left unconnected, the LT3651IUHE-4.2#TRPBF disables temperature monitoring and proceeds with charging normally. No pull-up or pull-down is required. However, removing NTC forfeits thermal safety protection, so this configuration is only recommended for controlled environments where battery temperature remains within 0°C–40°C at all times.

What is the function of the CLP and CLN pins on LT3651IUHE-4.2#TRPBF?

The CLP and CLN pins (Pins 29 and 30) form a differential input for system input current sensing. A sense resistor (R_CL) is placed between CLP and CLN to measure total input current drawn by both the charger and downstream system loads. The LT3651IUHE-4.2#TRPBF then dynamically reduces charge current to maintain the programmed input current limit set via the ILIM pin - enabling shared power rail management.

Does LT3651IUHE-4.2#TRPBF support both C/10 and timer-based charge termination simultaneously?

No - termination mode is selected at runtime. Connecting the TIMER pin to ground disables the internal timer, forcing C/10-only termination. Leaving TIMER open or connecting a capacitor enables timer-based termination, which overrides C/10 detection and continues charging beyond C/10 until timeout. The LT3651IUHE-4.2#TRPBF does not combine both methods; the designer chooses one strategy per application.