USB Battery Charger

Linear Technology announces the LTC3558, a multi-function power management solution for handheld applications. The LTC3558 integrates a stand-alone Li-Ion/Polymer battery charger and two synchronous regulators - one buck-boost and one buck - and is offered in a 3mm x 3mm QFN package. The linear battery charger can deliver up to 950mA charge current from a wall adapter supply, or up to 500mA charge current from a USB port. The LTC3558’s stand-alone autonomous operation simplifies design, eliminating the need for an external microprocessor for charge termination. Both switching regulators are designed to operate over the Li-Ion/Polymer range of 2.7V to 4.2V while delivering output currents up to 400mA each.

 The LTC3558’s integrated synchronous buck regulator features 100% duty cycle operation, while the buck-boost regulator is capable of regulating its programmed output voltage (typically 3.3V) over the entire Li-Ion/Polymer operating range. The integrated RDS(ON) switches enable efficiencies as high as 92%, maximizing battery run time. In addition, Burst Mode operation optimizes efficiency at light loads with a quiescent current of 20uA for the buck-boost and 35uA for the buck (<1uA in shutdown for each). The 2.25MHz switching frequency allows the utilization of tiny low cost capacitors and inductors less than 1mm in height. Furthermore, the regulators are stable with ceramic output capacitors.

 The LTC3558’s battery charger contains USB functionality, including 20%/100% full-scale charge current setting, a SUSP pin for shutdown/enable, and 4 different indication states on the /CHRG pin. The final battery float voltage is accurate to ±0.5%. The charger’s thermal regulation scheme maximizes the charge rate without the risk of overheating, while the NTC input allows temperature-qualified charging. To preserve battery energy, the LTC3558 draws <3uA from the battery in suspend mode. The charger is compatible with inputs up to 5.5V (7V absolute maximum transient for added robustness).

 Pricing starts at $2.35 each for 1,000-piece quantities.