Electronic Design

USB Power Solution Includes Switching Power Manager, Battery Charger, Three Synchronous Buck Regulators and LDO

Design Note 420

Linear Technology offers a variety of parts to simplify the task of extracting power from a battery or a USB cable. These devices seamlessly manage the power flow between an AC adapter, USB cable and Li-Ion battery, all while maintaining USB power specification compliance. As battery capacities rise, battery chargers must keep pace by steadily improving efficiency to minimize thermal concerns and charge times. A USB-based battery charger must squeeze as much power from the USB as possible, and do it efficiently to meet the stringent space and thermal constraints of today’s power-intensive applications.

The LTC®3555 combines a USB switching power manager and battery charger with three synchronous buck regulators and an LDO to provide a complete power supply solution in one small (4mm × 5mm) package (Figure 1). The constant-current, constant-voltage Lithium-Ion/Polymer charger utilizes a Bat-Track™ feature to maximize the efficiency of the battery charger by generating an input voltage that automatically tracks the battery voltage (described below). An I2C serial interface affords the system designer complete control over the charger and the DC/DC bucks for ultimate adaptability to changing operating modes in a wide range of applications.

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