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LTC4121/LTC4121-4.2 - 40V 400mA Synchronous Step-Down Battery Charger

The LTC®4121 is a 400mA constant-current/constantvoltage (CC/CV) synchronous step-down battery charger. In addition to CC/CV operation, the LTC4121 regulates its input voltage to a programmable percentage of the input open-circuit voltage. This technique maintains maximum power transfer with high impedance input sources such as solar panels.

An external resistor programs the charge current up to 400mA. The LTC4121-4.2 is suitable for charging Li-Ion/ Polymer batteries, while the programmable float voltage of the LTC4121 is suitable for several battery chemistries.

The LTC4121 and LTC4121-4.2 include an 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 LTC4121 signals end-ofcharge 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%.

Features Wide Input Voltage Range: 4.4V to 40V Temperature Compensated Input Voltage Regulation for Maximum Power Point Tracking (MPPT) Adjustable Float Voltage 3.5V to 18V (LTC4121) Fixed 4.2V Float Voltage Option (LTC4121-4.2) High Efficiency: Up to 95% 50mA to 400mA Programmable Charge Current ±1% Feedback Voltage Accuracy Programmable 5% Accurate Charge Current Thermally Enhanced, Low Profile (0.75mm) 16-Lead (3mm × 3mm) QFN Package Typical Application

Applications Handheld Instruments Solar Powered Devices Industrial/Military Sensors and Devices Packaging

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