Analog Devices Inc. LT3651IUHE-8.2#TRPBF

Overview

LT3651IUHE-8.2#TRPBF from Analog Devices (formerly Linear Technology) is a monolithic 4A, 2-cell Li-ion/Polymer battery charger IC with average current mode synchronous step-down architecture. It operates from 9V to 32V input, delivers ±0.5% float voltage accuracy at 8.2V, supports C/10 or programmable timer termination, and integrates NTC-based temperature monitoring for automotive cradle chargers and industrial handheld instruments.

For engineers reviewing the LT3651IUHE-8.2#TRPBF datasheet, LT3651IUHE-8.2#TRPBF pinout, LT3651IUHE-8.2#TRPBF application, or LT3651IUHE-8.2#TRPBF equivalent, key selection criteria include its 36-lead QFN package, 4A programmable charge current, 8.2V fixed float voltage, ±7.5% charge current accuracy, and integrated input current limiting via ILIM/CLP/CLN pins.

Technical Context

The LT3651IUHE-8.2#TRPBF implements an average current mode control loop using dual error amplifiers: V-EA regulates BAT voltage against an internal 8.2V reference, while C-EA compares a scaled-down ITH signal (10× sense voltage) with the SENSE–BAT voltage to enforce precise constant-current regulation. The switcher uses synchronous MOSFETs with BOOST-supplied high-side drive and supports user-programmable frequency via RT resistor (1.1MHz typical).

It features dual termination modes - C/10 detection (triggered at 4.5–12.3mV across RSENSE) or timer-based (3-hour default, adjustable via TIMER capacitor) - with auto-recharge at 97.5% of float voltage and preconditioning below 5.65V. Thermal foldback, bad battery detection, and input current limiting (via ILIM/CLP/CLN) are implemented in analog hardware without microcontroller dependency.

Key Specifications

Pinout & Package

LT3651IUHE-8.2#TRPBF is housed in a thermally enhanced 36-lead plastic QFN (UHE) package measuring 5mm × 6mm × 0.75mm. Exposed pad Pin 37 is GND and must be soldered to PCB ground plane; exposed pad Pin 38 is SW and requires low-inductance connection to power ground and inductor return path.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 2-cell Li-ion charger applications.

Compared with BQ24610RGER and MP2617GQ-Z, the LT3651IUHE-8.2#TRPBF uniquely combines monolithic 4A synchronous switching, 8.2V precision float, integrated NTC interface, and dual C/10/timer termination-making it optimal for automotive and industrial 2S chargers demanding autonomy and safety compliance.

Availability

LT3651IUHE-8.2#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, extended temperature operation (–40°C to 125°C), and long-term lifecycle support.

Supply support for LT3651IUHE-8.2#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, Inc. (ADI) is a global leader in high-performance analog, mixed-signal, and digital signal processing technologies, formed through the acquisition of Linear Technology in 2017.

The LT3651IUHE-8.2#TRPBF belongs to ADI's legacy Linear Technology battery management product line, designed specifically for high-voltage, high-current standalone Li-ion charging in harsh environments including automotive, industrial, and portable instrumentation.

FAQ

What is the exact float voltage of the LT3651IUHE-8.2#TRPBF and how is it trimmed?

The LT3651IUHE-8.2#TRPBF has a factory-trimmed nominal float voltage of 8.2V with guaranteed accuracy of ±0.5% over –40°C to 125°C junction temperature. This value is laser-trimmed during wafer test and is specific to the "-8.2" suffix variant-distinct from the LT3651-8.4 version which targets 8.4V. No external components affect this reference; it is internally generated and buffered to the BAT pin.

Can the LT3651IUHE-8.2#TRPBF be used with a 3-cell Li-ion battery?

No, the LT3651IUHE-8.2#TRPBF is strictly designed for 2-cell (2S) Li-ion/Polymer batteries with an 8.2V float voltage. Its internal reference, precondition threshold (5.65V), and recharge hysteresis (2.5% of 8.2V = 205mV) are fixed for 2S operation. Using it with a 3S battery would result in severe undercharging and failure to reach full capacity.

How does the LT3651IUHE-8.2#TRPBF implement input current limiting, and what external components are required?

The LT3651IUHE-8.2#TRPBF implements input current limiting using the CLP and CLN pins as a differential sense input, paired with the ILIM pin as a programming interface. A sense resistor (RCL) is placed between CLP and CLN, and a resistor (RILIM) connects ILIM to ground. The voltage on ILIM sets the maximum allowable voltage across RCL (70–115mV), thereby regulating total input current independently of battery charge current.

Does the LT3651IUHE-8.2#TRPBF support both C/10 and timer-based termination simultaneously?

No-the LT3651IUHE-8.2#TRPBF supports either C/10 termination or timer-based termination, selected by the state of the TIMER pin. If TIMER is left floating or pulled high, C/10 termination is active. If a capacitor is connected from TIMER to ground, timer-based termination is enabled and C/10 detection is overridden until timeout. Both modes cannot operate concurrently.

What is the thermal performance of the LT3651IUHE-8.2#TRPBF in its 36-lead QFN package?

The LT3651IUHE-8.2#TRPBF has a specified θJA of 43°C/W when mounted on a 4-layer PCB with proper thermal vias under the exposed GND (Pin 37) and SW (Pin 38) pads. With 4A charge current and 20V input, typical power dissipation is ~3.5W; under these conditions, the junction temperature rise above ambient is approximately 150°C-necessitating careful thermal design, copper area, and airflow to stay within the 125°C maximum rating.