Features

• Charges Single-Cell Li-Ion Batteries from Wall Adapter and USB Inputs
• Automatic Input Power Detection and Selection
• Charge Current Programmable Up to 950mA from Wall Adapter Input
• High Efficiency 600mA Synchronous DC/DC Converter
• No External MOSFET, Sense Resistor or Blocking Diode Needed
• Thermal Regulation Maximizes Charge Rate Without Risk of Overheating*
• Preset Charge Voltage with ±0.6% Accuracy
• Programmable Charge Current Termination
• 1.5MHz Constant Frequency Operation (Step-Down Converter)
• 18μA USB Suspend Current in Shutdown
• Independent “Power Present” Status Outputs
• Charge Status Output
• Automatic Recharge
• Available in a Thermally Enhanced, Low Profile (0.75mm) 16-Lead (5mm x 3mm) DFN Package

Typical Application

Description

The LTC3550-1 is a standalone linear charger with a 600mA monolithic synchronous buck converter. It is capable of charging a single-cell Li-Ion battery from both wall adapter and USB inputs. The charger automatically selects the appropriate power source for charging.

Internal thermal feedback regulates the battery charge current to maintain a constant die temperature during high power operation or high ambient temperature conditions. The float voltage is fixed at 4.2V and the charge currents are programmed with external resistors. The LTC3550-1 terminates the charge cycle when the charge current drops below the programmed termination threshold after the final float voltage is reached. With power applied to both inputs, the LTC3550-1 can be put into shutdown mode reducing the DCIN supply current to 20μA, the USBIN supply current to 10μA, and the battery drain current to less than 2μA.

The synchronous buck converter generates a fixed output voltage of 1.875V. The switching frequency is internally set at 1.5MHz, allowing the use of small surface mount inductors and capacitors.