Linear Adds Monolithic USB Battery Charger with Dual Synchronous Buck Converters
Linear Technology Corp. announced the LTC3559 – which is claimed to be an efficient, multi-function power management solution for handheld applications. The LTC3559 integrates a standalone Li-Ion/Polymer battery charger and two high efficiency synchronous buck regulators, and is offered in a low-profile 3mm x 3mm DFN 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 supply. It is said by the company to contains a high degree of 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. Standalone autonomous operation is claimed to simplify design, and to eliminate the need for an external microprocessor for charge termination. The final battery float voltage is accurate to ±0.4%. The charger’s patented 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 LTC3559 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).
The LTC3559’s integrated synchronous buck regulators feature 100% duty cycle operation and are capable of delivering output currents up to 400mA each, with programmable output voltages as low as 0.8V. The internal low RDS(ON) switches enable efficiencies as high as 90%, maximizing battery run time. In addition, Burst Mode® operation optimizes efficiency at light loads with a quiescent current of only 35uA (<1uA in shutdown). Using a constant frequency current mode architecture, the buck regulators operate from an input voltage range of 2.5 to 5.5V. The high 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, achieving very low output voltage ripple.
The LTC3559 is available from stock in a compact low-profile (0.75mm) 3mm x 3mm QFN-16 package. Pricing starts at $2.15 each for 1,000-piece quantities.
