Analog Devices Inc. LT3651IUHE-8.2#PBF

Overview

LT3651IUHE-8.2#PBF 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#PBF datasheet, LT3651IUHE-8.2#PBF pinout, LT3651IUHE-8.2#PBF application, or LT3651IUHE-8.2#PBF equivalent, key selection criteria include its 36-lead QFN package, 4A programmable charge current, ±7.5% charge current accuracy, dynamic input current limiting via ILIM, and auto-recharge trigger at 97.5% of 8.2V float voltage.

Technical Context

The LT3651IUHE-8.2#PBF implements an average current mode control loop using dual error amplifiers (V-EA and C-EA) to regulate constant-current/constant-voltage charging. Its synchronous switcher uses bootstrapped high-side drive (BOOST pin) and MOSFET low-side switching, with internal 125°C thermal protection and precision undervoltage lockout via SHDN pin (1.20V threshold, 95mV hysteresis).

Charge termination is configurable: C/10 detection (4.5–12.3mV sense threshold) or user-programmable timer (3-hour default via 0.68µF on TIMER pin). Preconditioning activates below 5.65V BAT, reducing charge current to 15% of programmed maximum until VBAT exceeds that threshold.

Key Specifications

Pinout & Package

LT3651IUHE-8.2#PBF is housed in a 36-lead plastic QFN (5mm × 6mm, 0.75mm height) with two exposed thermal pads: Pin 37 (GND) and Pin 38 (SW), both requiring PCB soldering for thermal and electrical integrity.

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 MP2617GQZ, the LT3651IUHE-8.2#PBF provides higher integration (synchronous switches, NTC interface, dual termination), tighter float voltage accuracy (±0.5% vs ±1%), and unique input current limiting-making it optimal for demanding 4A, thermally constrained, or safety-critical 2-cell applications.

Availability

LT3651IUHE-8.2#PBF is available at Aetrix Electronics and suitable for automotive cradle chargers, industrial handheld instruments, notebook docking stations, and medical device cradles requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LT3651IUHE-8.2#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 (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving precision instrumentation, industrial, automotive, and communications markets.

The LT3651 product line delivers monolithic, high-voltage, high-current Li-Ion chargers optimized for 12V–32V input systems where space, thermal performance, and functional safety are critical-targeting automotive, industrial, and medical portable equipment.

FAQ

What is the exact float voltage specification for LT3651IUHE-8.2#PBF?

The LT3651IUHE-8.2#PBF is factory-trimmed to deliver a nominal battery float voltage of 8.2V with ±0.5% accuracy over the full –40°C to +125°C junction temperature range. This value is fixed per part number variant and applies specifically to the LT3651-8.2 family; the LT3651-8.4 variant is trimmed to 8.4V. The specification is guaranteed by design and characterization, not typical-only.

How does LT3651IUHE-8.2#PBF implement input current limiting?

The LT3651IUHE-8.2#PBF implements input current limiting using the CLP/CLN pins to sense system input current and the ILIM pin to program the limit. A resistor from ILIM to ground sets the maximum allowable voltage across the CLP–CLN sense resistor; the IC then dynamically reduces charge current to maintain that input current ceiling, enabling stable operation from current-limited sources like automotive alternators or shared DC rails.

Can LT3651IUHE-8.2#PBF operate without an NTC thermistor?

Yes, the LT3651IUHE-8.2#PBF can operate without an NTC thermistor: the NTC pin (Pin 1) may be left unconnected, disabling temperature monitoring. In this configuration, all thermal safety functions tied to NTC (e.g., charging suspension outside 0°C–40°C) are inactive, but all other charging features-including CC/CV regulation, preconditioning, C/10 or timer termination, and input current limiting-remain fully functional.

What is the purpose of the RNG/SS pin on LT3651IUHE-8.2#PBF?

On the LT3651IUHE-8.2#PBF, the RNG/SS (Pin 35) serves two primary functions: (1) it programs the maximum charge current via a resistor-to-ground (50µA sourced, 10× gain for SENSE–BAT voltage), and (2) it enables soft-start by adding a capacitor from RNG/SS to ground, which ramps the charge current gradually to limit inrush and stabilize the power stage during startup.

Does LT3651IUHE-8.2#PBF support automatic recharge after battery voltage drop?

Yes, the LT3651IUHE-8.2#PBF supports automatic recharge: when the battery voltage at the BAT pin drops 2.5% below the 8.2V float voltage (i.e., to 8.0V), the IC initiates a new charging cycle. This behavior occurs in standby mode, where VIN supply current remains below 85µA, and requires no external intervention or controller interaction.