Analog Devices Inc. DC1750A

Overview

LTC4054L-4.2 from Analog Devices (formerly Linear Technology) is a standalone linear lithium-ion battery charger IC designed for single-cell coin cell and low-capacity Li-ion batteries. It delivers programmable constant-current/constant-voltage charging up to 150mA, features ±1% 4.2V float voltage regulation, thermal feedback for safe operation, and automatic C/10 charge termination - all in a 5-lead TSOT-23 package. It is optimized for USB-powered portable devices such as wireless headsets and multifunction wristwatches.

For engineers reviewing the LTC4054L-4.2 datasheet, LTC4054L-4.2 pinout, LTC4054L-4.2 application, or LTC4054L-4.2 equivalent, key selection considerations include its 4.2V fixed float voltage, 10–150mA programmable charge current range, integrated MOSFET architecture eliminating external sense resistors and blocking diodes, and its thermal regulation behavior at junction temperatures ≥120°C.

Technical Context

The LTC4054L-4.2 implements a fully autonomous linear charging algorithm with three operational phases: trickle charge (VBAT < 2.9V), constant-current (CC) mode (programmable 10–150mA), and constant-voltage (CV) mode (4.2V ±1%). Its internal P-channel power FET (RON = 1.5Ω typ.) enables direct battery connection without external components.

Charge control is managed via the PROG pin, which serves dual roles: programming current using RPROG (IBAT = 150 × VPROG/RPROG) and enabling manual shutdown (floating PROG > 1.21V). The CHRG pin provides open-drain status output with strong pull-down (~10mA) during active charge, weak pull-down (~20µA) in standby, and high-impedance during UVLO.

Key Specifications

Pinout & Package

Package: 5-lead Low-Profile (1mm height) TSOT-23 (S5), RoHS-compliant, with exposed pad for thermal enhancement.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MCP73831T-2DCI/OT and BQ24040DRCR, the LTC4054L-4.2 uniquely balances ultra-low quiescent current (25µA shutdown), precise 4.2V regulation (±1%), and built-in thermal limiting - making it the only option validated for sub-100mA coin-cell charging with automatic deep-discharge recovery and minimal external components.

Availability

LTC4054L-4.2 is available at Aetrix Electronics and suitable for wireless headsets, Bluetooth earbuds, and multifunction wristwatches requiring stable component supply, long-term lifecycle support, and guaranteed RoHS-compliant manufacturing.

Supply support for LTC4054L-4.2 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 digital signal processing semiconductors.

The LTC4054L-4.2 belongs to Linear's legacy "ThinSOT Battery Charger" product line, engineered specifically for space- and power-constrained portable electronics using single-cell Li-ion coin batteries and USB-compatible inputs.

FAQ

What is the exact float voltage and tolerance of the LTC4054L-4.2?

The LTC4054L-4.2 has a fixed regulated float voltage of 4.2V with a total accuracy of ±1% over the full operating temperature range (–40°C to 85°C). This value is trimmed at wafer test and does not require external components for calibration. Measured VFLOAT remains within 4.158V to 4.242V under specified conditions (IBAT = 40mA, TA = 0°C to 85°C), ensuring safe and repeatable full-charge termination for standard Li-ion chemistry.

How is charge current programmed on the LTC4054L-4.2?

Charge current on the LTC4054L-4.2 is set using a single 1% tolerance resistor (RPROG) connected between the PROG pin and GND. The relationship is defined as IBAT = 150 × VPROG / RPROG, where VPROG is held at 1.0V (±3%) in constant-current mode. For example, a 1.69kΩ resistor yields ~90mA (150V / 1.69kΩ). The PROG pin also functions as a real-time current monitor - measuring its voltage allows continuous calculation of actual IBAT.

Does the LTC4054L-4.2 support trickle charging, and what is its threshold?

Yes, the LTC4054L-4.2 supports trickle charging for deeply discharged batteries. It activates trickle mode when BAT voltage falls below 2.9V (typical), delivering approximately 1/10 of the programmed full-scale current. The threshold has ±0.1V tolerance and includes 80mV hysteresis (VTRHYS) to prevent oscillation near the transition point. This ensures safe pre-conditioning of Li-ion cells before entering constant-current mode.

What happens to the CHRG pin during different operating states of the LTC4054L-4.2?

The CHRG pin on the LTC4054L-4.2 operates in three distinct states: (1) Strong pull-down (~10mA) during active charging - suitable for driving LEDs directly; (2) Weak pull-down (~20µA) in standby after charge termination - indicates ready-to-charge status with valid VCC; (3) High-impedance during undervoltage lockout (UVLO) - occurs when VCC < 3.8V or VCC − VBAT < 30mV. These states enable unambiguous microcontroller detection using simple resistor-divider sampling.

Can the LTC4054L-4.2 be used without a battery connected?

No - the LTC4054L-4.2 requires a battery or equivalent capacitive load on the BAT pin for stable constant-voltage loop operation. Without a battery, the CV feedback loop becomes unstable and may oscillate or fail to regulate. If no battery is present during testing, a minimum 10µF low-ESR ceramic capacitor (with optional 1Ω series resistor) must be placed at BAT to emulate battery impedance and ensure proper regulation and termination behavior.