説明

The LTC4120 is a constant-current/constant-voltage wireless receiver and battery charger. An external programming resistor sets the charge current up to 400mA. The LTC4120-4.2 is suitable for charging Li-Ion/Polymer batteries, while the programmable float voltage of the LTC4120 accommodates several battery chemistries. The LTC4120 uses a Dynamic Harmonization Control (DHC) technique that allows high efficiency contactless charging across an air gap.

The LTC4120 regulates its input voltage via the DHC pin. This technique modulates the resonant frequency of a receiver tank to automatically adjust the power received as well as the power transmitted to provide an efficient solution for wirelessly charging battery-powered devices.

Wireless charging with the LTC4120 provides a method to power devices in harsh environments without requiring expensive failure-prone connectors. This allows products to be charged while locked within sealed enclosures, or in moving or rotating equipment, or where cleanliness or sanitation is critical.

This full featured battery charger includes accurate RUN pin threshold, low voltage battery preconditioning and bad battery fault detection, timer termination, auto-recharge, and NTC temperature qualified charging. The FAULT pin provides an indication of bad battery or temperature faults.

Once charging is terminated, the LTC4120 signals end-of charge via the CHRG pin, and enters a low current sleep mode. An auto-restart feature starts a new charging cycle if the battery voltage drops by 2.2%.

 

特徴

Dynamic Harmonization Control Optimizes Wireless Charging Over a Wide Coupling Range

Wide Input Voltage Range (12.5V to 40V)

Adjustable Float Voltage (3.5V to 11V)

Fixed 4.2V Float Voltage Option (LTC4120-4.2)

50mA to 400mA Charge Current Programmed with a Single Resistor

±1% Feedback Voltage Accuracy

Programmable 5% Accurate Charge Current

No Microprocessor Required

No Transformer Core

Thermally Enhanced, Low Profile 16-Lead (3mm × 3mm × 0.75mm) QFN Package

 

アプリケーション

Handheld Instruments

Industrial/Military Sensors and Devices

Harsh Environments

ポータブル医療機器

Physically Small Devices

Electrically Isolated Devices

 

オペレーション

Wireless Power System Overview

The LTC4120 is one component in a complete wireless power system. A complete system is composed of transmit circuitry, a transmit coil, a receive coil and receive circuitry—including the LTC4120.In particular, the Resonant Transmitter and Receiver and the Alternative Transmitter Options sections include information necessary to complete the design of a wireless power system.

LTC4120 Overview

The LTC4120 is a synchronous step-down (buck) wireless battery charger with dynamic harmonization control (DHC). DHC is a highly efficient method of regulating the received input voltage in a resonant coupled power transfer application. The LTC4120 serves as a constant-current/ constant-voltage battery charger with the following builtin charger functions: programmable charge current, programmable float voltage (LTC4120), battery precondition with half-hour timeout, precision shutdown/run control, NTC thermal protection, a 2-hour safety termination timer, and automatic recharge. The LTC4120 also provides output pins to indicate state of charge and fault status.

Wireless Power Transfer

The receiver consists of a coil, LR, configured in a resonant circuit followed by a rectifier and the LTC4120. The receiver coil presents a load reflected back to the transmitter through the mutual inductance between LR and LX. The reflected impedance of the receiver may influence the operating frequency of the transmitter. Likewise, the power output by the transmitter depends on the load at the receiver. The resonant coupled charging system, consisting of both the transmitter and LTC4120 charger, provides an efficient method for wireless battery charging as the power output by the transmitter varies automatically based on the power used to charge a battery.

Precision Run/Shutdown Control

The LTC4120 remains in a low power disabled mode until the RUN pin is driven above VEN (typically 2.45V). While the LTC4120 is in disabled mode, current drain from the battery is reduced to extend battery lifetime, the status pins are both de-asserted, and the FBG pin is high impedance. Charging can be stopped at any time by pulling the RUN pin below 2.25V. The LTC4120 also offers an extremely low operating current shutdown mode when the RUN pin is pulled below VSD (typically 0.7V). In this condition less than 20µA is drawn from the supply at IN.