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

Product Details

The LTC4121 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%.


  • Handheld Instruments
  • Solar Powered Devices
  • Industrial/Military Sensors and Devices

Features and Benefits

  • 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