Analog Devices Inc. LT3651IUHE-4.2#PBF

Overview

LT3651IUHE-4.2#PBF 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 7.5% charge current accuracy, 0.5% float voltage accuracy, and NTC-based temperature monitoring. It is used in automotive cradle chargers and industrial handheld instruments requiring robust wide-input charging.

For engineers reviewing the LT3651IUHE-4.2#PBF datasheet, LT3651IUHE-4.2#PBF pinout, LT3651IUHE-4.2#PBF application, or LT3651IUHE-4.2#PBF equivalent, key selection considerations include its 36-pin QFN package, programmable 4A charge current, C/10 or timer-based termination, thermal foldback protection, and integrated average current mode control for high-efficiency CC/CV charging.

Technical Context

The LT3651IUHE-4.2#PBF implements an average current mode synchronous buck regulator with bootstrapped high-side drive and MOSFET low-side switch, operating at user-programmable frequencies (250kHz–1.1MHz via RT pin). Its dual-loop architecture uses V-EA to regulate battery voltage and C-EA to regulate average inductor current via SENSE–BAT differential sensing.

It integrates precision analog comparators for preconditioning (VBAT < 2.9V), auto-recharge (VBAT < 97.5% × 4.2V), bad battery detection (precondition timeout ≤22.5 min), and thermal foldback (reducing ICHG above TJ > 125°C). Input current limiting is enforced via CLP/CLN sense resistor feedback controlled by ILIM pin voltage.

Key Specifications

Pinout & Package

LT3651IUHE-4.2#PBF is housed in a 36-pin plastic QFN package (5mm × 6mm, 0.75mm profile) with two exposed thermal pads: Pin 37 (GND) and Pin 38 (SW), both requiring direct PCB soldering for electrical integrity and thermal dissipation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC4015IUHF#PBF and BQ24610RGER, the LT3651IUHE-4.2#PBF delivers superior thermal safety integration and autonomous preconditioning without MCU dependency, making it optimal for standalone, high-reliability industrial charging where analog robustness is prioritized over digital configurability.

Availability

LT3651IUHE-4.2#PBF is available at Aetrix Electronics and suitable for automotive cradle chargers, industrial handheld instruments, desktop battery cradles, and notebook computer docking stations requiring stable component supply and guaranteed industrial temperature operation.

Supply support for LT3651IUHE-4.2#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, Inc. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving industrial, automotive, communications, and healthcare markets.

The LT3651IUHE-4.2#PBF belongs to Linear's high-voltage Li-ion charger product line, designed specifically for wide-input, high-current, thermally robust charging in harsh environments where reliability and analog autonomy are critical.

FAQ

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

The LT3651IUHE-4.2#PBF 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 is confirmed in the Electrical Characteristics table (Page 3) of the official datasheet, distinguishing it from the LT3651-4.1 variant (4.1V).

Does LT3651IUHE-4.2#PBF support automatic recharge, and at what threshold?

Yes, the LT3651IUHE-4.2#PBF supports automatic recharge when battery voltage drops to 97.5% of its float voltage - i.e., 4.1V (4.2V × 0.975). This behavior is hard-coded and does not require external components; the IC restarts a full CC/CV cycle upon detecting this condition at the BAT pin.

How is input current limiting implemented on LT3651IUHE-4.2#PBF?

Input current limiting on the LT3651IUHE-4.2#PBF is implemented using the CLP and CLN pins with an external sense resistor (RCL), where voltage across RCL is regulated by the ILIM pin voltage. A 1V input on ILIM corresponds to 95mV across RCL, enabling precise system-level current control independent of battery state or charge phase.

What thermal protection mechanisms does LT3651IUHE-4.2#PBF include?

The LT3651IUHE-4.2#PBF includes three thermal protections: (1) NTC-based battery temperature monitoring (0°C–40°C window), (2) die temperature foldback that reduces charge current above 125°C, and (3) overtemperature shutdown with automatic recovery. These are fully analog and require no firmware intervention.

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

Yes, the LT3651IUHE-4.2#PBF operates without an NTC thermistor - the NTC pin (Pin 1) can be left unconnected. In that case, temperature-based fault detection and charging suspension are disabled, but all other functions (CC/CV, timer, preconditioning, input limiting) remain fully operational.