Standalone Linear Li-Ion Battery Charger and Dual Synchronous Buck Converter

The LTC3552 is a complete constant-current/constant voltage 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 specifications.

No external sense resistor or external blocking diode is required due to the internal MOSFET architecture. The charge voltage is fixed 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 final float 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.

Vout

LTC3552

Adjustable (0.6V to 5V)

LTC3552-1

1.8V & 1.575V

Applications

* Cellular Telephones, PDAs, MP3 Players

* Bluetooth Applications

* Programmable Charge Current Up to 950mA

* Complete Linear Charger and Dual DC/DC Regulator

* Buck Converter Output Voltage from 0.6V to 5V

* No MOSFET, Sense Resistor or Blocking Diode Required

* Thermal Regulation Maximizes Charge Rate Without Risk of Overheating*

* Charges Directly from a USB Port

* Programmable Charge Current Termination

* Preset 4.2V Charge Voltage with ±1% Accuracy