Analog Devices Inc. LTC4009IUF-2#PBF

Overview

LTC4009IUF-2#PBF from Analog Devices (formerly Linear Technology) is a synchronous buck battery charger controller optimized for lithium-ion/polymer packs with 1–4 series cells. It delivers ±0.5% float voltage accuracy at 4.2 V/cell, supports 6–28 V input and 2–28 V output ranges, and features programmable charge current (±4% accuracy), AC adapter input current limiting (±3% accuracy), and 550 kHz quasi-constant-frequency PWM to eliminate audible noise with ceramic capacitors - used in notebook computers and portable instrumentation.

For engineers reviewing the LTC4009IUF-2#PBF datasheet, LTC4009IUF-2#PBF pinout, LTC4009IUF-2#PBF application, or LTC4009IUF-2#PBF equivalent, key selection criteria include its I-grade (–40°C to 125°C) operation, pin-programmable 4.2 V/cell output, external termination control, analog charge current monitoring via PROG, and thermally enhanced 20-pin 4 mm × 4 mm QFN package with exposed GND pad.

Technical Context

The LTC4009IUF-2#PBF implements a current-mode synchronous buck topology with fixed 550 kHz nominal switching frequency and adaptive duty cycle up to 99%. Its error amplifier compares VFB against a 1.2085 V reference and regulates charge current via ITH-controlled peak inductor current sensing through CSP/CSN.

It integrates dual-loop control: constant-current regulation using PROG-based current feedback and constant-voltage regulation via FVS0/FVS1-selectable 4.2 V/cell output (LTC4009-2 variant), with independent AC adapter current limiting enforced by CLP/CLN differential sensing and signaled via open-drain ICL output.

Key Specifications

Pinout & Package

Package: 20-lead (4 mm × 4 mm × 0.75 mm) plastic QFN with exposed thermal pad (Pin 21 = GND), θ_JA = 37°C/W. Requires soldering of exposed pad to PCB ground plane for thermal and electrical integrity.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar battery charger controller applications.

Compared with LTC4009IUF-1#PBF, the LTC4009IUF-2#PBF delivers higher 4.2 V/cell float voltage essential for modern high-capacity Li-ion cells, while BQ24725ARGRT adds digital control at the cost of external component count reduction and loss of analog current monitoring flexibility.

Availability

LTC4009IUF-2#PBF is available at Aetrix Electronics and suitable for notebook computers, portable instrumentation, and battery backup systems requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LTC4009IUF-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 maintains full product support, documentation, and manufacturing continuity for the LTC portfolio.

The LTC4009 family is designed as a flexible, high-efficiency synchronous buck charger controller platform for multi-cell Li-ion, Li-polymer, and other chemistries - emphasizing precision voltage/current regulation, external algorithm control, and robust thermal performance.

FAQ

What battery chemistries does the LTC4009IUF-2#PBF support?

The LTC4009IUF-2#PBF supports lithium-ion and lithium-polymer battery packs with 1–4 series cells configured for 4.2 V/cell output. It does not include built-in charge termination, so external microcontroller control is required for full CC/CV algorithms, preconditioning, or safety cutoffs. The device's wide 2–28 V output range and programmable current also allow adaptation to lead-acid, NiMH, or custom chemistries with appropriate host firmware and external sensing.

How is the 4.2 V/cell output set on the LTC4009IUF-2#PBF?

The LTC4009IUF-2#PBF uses dedicated FVS0 and FVS1 pins (Pins 9 and 10) to select 4.2 V/cell output. When both pins are tied to INTVDD (5 V), the internal resistor network configures the feedback reference for exactly 4.2 V per cell - eliminating the need for external voltage-divider resistors used in the base LTC4009 variant. This pin-strapping method ensures consistent, temperature-stable output without calibration.

Does the LTC4009IUF-2#PBF include built-in charge termination?

No, the LTC4009IUF-2#PBF does not include built-in charge termination. It is a controller IC requiring external circuitry - typically a microcontroller - to manage full charge algorithms, including C/10 detection (signaled via CHRG pin), timer-based cutoff, temperature monitoring, and safety shutdown. The CHRG pin provides three-state status (bulk, C/10, shutdown), but final termination decision and action reside with the host system.

What is the purpose of the PROG pin on the LTC4009IUF-2#PBF?

The PROG pin on the LTC4009IUF-2#PBF serves two functions: it programs maximum charge current via an external resistor to GND, and it provides an analog voltage output (11.67 µA/mV) linearly proportional to actual charge current. This enables real-time current monitoring without additional sensing components - the host MCU can read PROG voltage to implement dynamic current adjustment, telemetry logging, or fault detection based on current deviation.

Can the LTC4009IUF-2#PBF operate with ceramic output capacitors without audible noise?

Yes, the LTC4009IUF-2#PBF uses a quasi-constant 550 kHz PWM architecture that avoids sub-audible frequency modulation, enabling silent operation with ceramic output capacitors. This eliminates piezoelectric noise common in variable-frequency controllers and allows use of small, high-reliability MLCCs instead of bulkier, less stable electrolytic or tantalum types - confirmed in typical application circuits and performance graphs in the official datasheet.