Analog Devices Inc. LT3650IDD-4.2#PBF

Overview

LT3650IDD-4.2#PBF from Analog Devices (formerly Linear Technology) is a monolithic 2A step-down Li-Ion/Polymer battery charger IC with 4.75V–32V input range, 4.2V float voltage, and integrated 2.5A switch. It delivers constant-current/constant-voltage charging with C/10 or timer-based termination, preconditioning for deeply discharged batteries, and NTC temperature monitoring. It is used in 12V–24V automotive cradle chargers requiring robust high-voltage battery management.

For engineers reviewing the LT3650IDD-4.2#PBF datasheet, LT3650IDD-4.2#PBF pinout, LT3650IDD-4.2#PBF application, or LT3650IDD-4.2#PBF equivalent, key selection considerations include its 4.2V float voltage accuracy (±0.5%), programmable 2A charge current via external sense resistor, internal 3-hour safety timer, auto-recharge at 97.5% float voltage, and DFN-12 (3mm × 3mm) package with exposed thermal pad.

Technical Context

The LT3650IDD-4.2#PBF implements average current mode control at 1MHz fixed frequency, using an internal 2.5A switch driven by a bootstrapped BOOST rail referenced to SW. Its voltage error amplifier (V-EA) regulates BAT pin voltage against a precision 4.2V reference, while the current error amplifier (C-EA) servo-controls average inductor current via SENSE–BAT differential sensing.

Charge termination is configurable: either when sensed current falls to C/10 (i.e., 10% of programmed IMAX), or after a user-programmed time (e.g., 3 hours with 0.68µF on TIMER pin). Preconditioning activates below 2.9V battery voltage, reducing charge current to 15% of IMAX; bad-battery detection triggers if precondition persists beyond 22.5 minutes (1/8 of full timer cycle).

Key Specifications

Pinout & Package

LT3650IDD-4.2#PBF is housed in a 12-pin plastic DFN package (3mm × 3mm, 0.75mm height) with exposed thermal pad (Pin 13) soldered to PCB ground for thermal management.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LT3650EDD-4.2#PBF, the LT3650IDD-4.2#PBF guarantees full specification compliance down to –40°C, making it suitable for automotive and outdoor industrial use; compared with BQ24610RGER, it eliminates external FETs and gate drivers while adding autonomous preconditioning and binary status signaling.

Availability

LT3650IDD-4.2#PBF is available at Aetrix Electronics and suitable for automotive cradle chargers, industrial handheld instruments, desktop docking stations, and notebook auxiliary power systems requiring stable component supply across extended temperature ranges.

Supply support for LT3650IDD-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 acquired Linear Technology in 2017 and continues to manufacture and support its high-performance analog and power management portfolio.

The LT3650IDD-4.2#PBF belongs to the LT3650 family of high-voltage monolithic Li-Ion chargers, designed specifically for industrial and automotive applications where wide-input voltage tolerance, integrated safety features, and minimal external component count are critical.

FAQ

What is the exact float voltage of the LT3650IDD-4.2#PBF?

The LT3650IDD-4.2#PBF has a nominal float voltage of 4.2V, specified as 4.18V (min) to 4.24V (max) at 25°C, with ±0.5% accuracy over temperature. This value is factory-trimmed and applies exclusively to the -4.2 variant; the -4.1 version targets 4.1V. The LT3650IDD-4.2#PBF does not support user-adjustable float voltage - it is fixed and internally calibrated.

Does the LT3650IDD-4.2#PBF require an external blocking diode on the VIN line?

No, the LT3650IDD-4.2#PBF does not require an external blocking diode on VIN. It integrates reverse-voltage protection circuitry that prevents battery discharge back into the input supply when VIN is absent or lower than battery voltage. This eliminates diode forward drop losses and simplifies layout - a key advantage confirmed in the device's Absolute Maximum Ratings and Applications Information sections.

How is charge current programmed on the LT3650IDD-4.2#PBF?

Charge current on the LT3650IDD-4.2#PBF is programmed using an external sense resistor (R_SENSE) between SENSE and BAT pins, where R_SENSE = 0.1V / I_MAX. For example, a 50mΩ resistor sets I_MAX = 2A. Additionally, the RNG/SS pin allows dynamic scaling: sourcing 50µA into a resistor (e.g., 20kΩ → 1V) sets full-scale current, while lower voltages proportionally reduce IMAX. The LT3650IDD-4.2#PBF does not use digital interfaces or resistive DACs for this function.

What happens during precondition mode on the LT3650IDD-4.2#PBF?

When the LT3650IDD-4.2#PBF detects V_BAT < 2.9V (with 90mV hysteresis), it enters precondition mode: charge current is reduced to 15% of the programmed I_MAX, and the internal timer begins counting. If V_BAT does not rise above 2.9V within 22.5 minutes (1/8 of full 3-hour timer cycle), a bad-battery fault is asserted - CHRG goes high-Z and FAULT is pulled low. The LT3650IDD-4.2#PBF exits precondition automatically once V_BAT exceeds the threshold.

Can the LT3650IDD-4.2#PBF be used with lithium iron phosphate (LiFePO₄) batteries?

No, the LT3650IDD-4.2#PBF is not suitable for LiFePO₄ batteries. Its fixed 4.2V float voltage and precondition threshold (2.9V) are optimized for standard Li-Ion/Li-Polymer chemistry. LiFePO₄ requires ~3.6V float and different charge profile parameters. Using the LT3650IDD-4.2#PBF with LiFePO₄ would result in overcharging and potential safety hazard. Analog Devices does not specify or characterize the LT3650IDD-4.2#PBF for LiFePO₄ use.