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USB battery charger integrates buck-boost, buck converters

Posted: 23 May 2008 ?? ?Print Version ?Bookmark and Share

Keywords:battery chargers? USB? buck-boost regulator?

Linear Technology Corp. has announced the LTC3558, an efficient, multifunction power management solution for handheld applications. The LTC3558 integrates a standalone Li-ion/polymer battery charger and two high-efficiency synchronous regulatorsone buck-boost and one buckand is offered in a compact low-profile 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 standalone 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 2.7-4.2V while delivering output currents up to 400mA each.

The LTC3558's integrated synchronous buck regulator features 100-percent 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 low Rds(on) switches enable efficiencies as high as 92 percent, maximizing battery run time. In addition, Burst Mode operation optimizes efficiency at light loads with a quiescent current of only 20?for the buck-boost and 35?for the buck (<1?in shutdown for each). 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 LTC3558's battery charger contains a high degree of USB functionality, including 20 percent/100 percent full-scale charge current setting, SUSP pin for shutdown/enable and four different indication states on the /CHRG pin. The final battery float voltage is accurate to 0.5 percent. 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 LTC3558 draws <3?from the battery in suspend mode. The charger is compatible with inputs up to 5.5V (7V absolute maximum transient for added robustness).

The LTC3558 is available from stock in a compact low-profile (0.75mm) 3mm x 3mm QFN-20 package. Pricing starts at $2.35 each for 1,000-piece quantities.

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