The LTC3552 is a complete constant-current/constantvoltage linear charger with a dual DC/DC converter for single cell lithium-ion batteries. Its DFN package and low external component count make the LTC3552 ideally suited for portable applications. Furthermore, the LTC3552 is designed to work within USB power speci? cations. No external sense resistor or external blocking diode is required due to the internal MOSFET architecture. The charge voltage is ?xed at 4.2V and the charge current is programmed with a resistor. The charge cycle terminates when the charge current drops below the programmed termination threshold after the ?nal ?oat voltage is reached. When the input supply (wall adapter or USB supply) is removed, the LTC3552 enters a low current state dropping the battery drain current to less than 2µA. Thermal regulation maximizes charge rate without risk of overheating. The synchronous step-down switching regulators generate adjustable output voltages from 5V down to 0.6V. The switching frequency is set at 2.25MHz, allowing the use of small surface mount inductors and capacitors.
