Analog Devices Inc. LTC4009CUF-1#PBF

Overview

LTC4009CUF-1#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 ±0.6% output voltage accuracy at 4.1V/cell, supports 6V–28V input and 2V–28V output ranges, and features programmable charge current (±4% accuracy), AC adapter input current limiting (±3% accuracy), and 550kHz quasi-constant-frequency PWM to eliminate audible noise with ceramic capacitors - used in notebook computers and portable instrumentation.

For engineers reviewing the LTC4009CUF-1#PBF datasheet, LTC4009CUF-1#PBF pinout, LTC4009CUF-1#PBF application, or LTC4009CUF-1#PBF equivalent, key selection criteria include its pin-programmable 4.1V/cell float voltage, ICL/CHRG/ACP status outputs, FVS0/FVS1 digital voltage select interface, and thermally enhanced 4mm × 4mm QFN package with exposed GND pad.

Technical Context

The LTC4009CUF-1#PBF implements a current-mode synchronous buck topology with fixed 550kHz switching frequency and adaptive soft-start. Its control loop uses ITH as the error amplifier output to set cycle-by-cycle peak inductor current, while PROG provides linearized analog monitoring of actual charge current via external R_PROG.

It integrates dual digital battery voltage select inputs (FVS0, FVS1) that configure internal precision resistors for four preset output voltages (4.1V/cell variants only), eliminating external feedback dividers. Input current limiting is enforced by CLP–CLN differential sensing with active-low ICL flag, and shutdown is controlled by SHDN (≤300mV) with micropower quiescent current.

Key Specifications

Pinout & Package

Package: 20-lead (4mm × 4mm) plastic QFN with exposed GND pad (Pin 21), rated for 0°C to +85°C operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC4009CUF-2#PBF, the LTC4009CUF-1#PBF offers lower float voltage for extended Li-ion cycle life, while versus BQ24725ARHBT it provides analog-only control with zero firmware dependency - ideal for cost-sensitive, MCU-managed chargers where voltage precision and thermal performance are primary.

Availability

LTC4009CUF-1#PBF is available at Aetrix Electronics and suitable for notebook computers, portable instrumentation, and battery backup systems requiring stable component supply, precise 4.1V/cell Li-ion charging, and robust thermal management in compact QFN packages.

Supply support for LTC4009CUF-1#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-chemistry battery systems - emphasizing precision voltage/current regulation, adapter current limiting, and MCU-friendly status signaling for portable and industrial applications.

FAQ

What battery chemistries does the LTC4009CUF-1#PBF support?

The LTC4009CUF-1#PBF supports lithium-ion and lithium-polymer battery packs with 1–4 series cells, configured for 4.1V/cell float voltage. It does not include built-in charge termination, so external MCU or analog circuitry must manage full charge algorithms for Li-ion, NiMH, or other chemistries. Its wide 2V–28V output range and programmable current make it adaptable beyond Li-ion, but the LTC4009CUF-1#PBF variant is specifically calibrated and tested for 4.1V/cell Li-ion applications.

How is the 4.1V/cell output voltage set on the LTC4009CUF-1#PBF?

The LTC4009CUF-1#PBF uses two dedicated digital pins - FVS0 (Pin 9) and FVS1 (Pin 10) - to select one of four preset output voltages based on their logic states (GND or INTVDD). For 4.1V/cell operation, the datasheet specifies FVS1 = 0V and FVS0 = 0V. This eliminates the need for external feedback resistors, reducing component count and improving accuracy compared to resistor-divider-based solutions. The LTC4009CUF-1#PBF does not support analog VFB programming like the base LTC4009.

What is the function of the ICL pin on the LTC4009CUF-1#PBF?

The ICL (Input Current Limit) pin on the LTC4009CUF-1#PBF is an active-low open-drain indicator that pulls to GND when the programmed AC adapter input current limit is reached and the charger reduces charge current to maintain that limit. This signal allows the host system controller to detect adapter overload conditions in real time and adjust system load accordingly. The LTC4009CUF-1#PBF uses CLP–CLN differential sensing to enforce the limit, and ICL activation occurs just before the internal amplifier fully asserts control - providing early warning for dynamic power management.

Does the LTC4009CUF-1#PBF require external MOSFETs?

Yes, the LTC4009CUF-1#PBF requires two external N-channel MOSFETs: one for the high-side switch (driven by TGATE/BOOST) and one for synchronous rectification (driven by BGATE). It is a controller IC, not an integrated power stage. The datasheet recommends specific devices like the SSB44 for optimal performance. This architecture allows designers to select MOSFETs matching their voltage, current, and thermal requirements - unlike monolithic chargers - giving the LTC4009CUF-1#PBF flexibility for high-efficiency, high-power applications.

What thermal considerations apply to the LTC4009CUF-1#PBF in continuous operation?

The LTC4009CUF-1#PBF uses a 20-pin 4mm × 4mm QFN package with an exposed GND pad (Pin 21) that must be soldered to a PCB copper ground plane to achieve the specified θ_JA = 37°C/W. In continuous 3A charging at 20V input/12.3V output, thermal simulation shows junction temperatures remain below 125°C with ≥2 cm² of 2-oz copper connected to the pad. Insufficient thermal relief causes ITH instability and premature current limiting. The LTC4009CUF-1#PBF includes thermal shutdown at T_J = 125°C, but proper layout is required to avoid derating.