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Switch Mode USB Power Manager & Triple Buck Regulator from Linear Technology

1st November 2007

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Linear Technology has announced the LTC3555, the first in a family of next generation multi-function power management solutions for Li-Ion/Polymer battery applications. The LTC3555 integrates a switching PowerPath manager, a standalone battery charger, an ideal diode, I2C control, three high efficiency synchronous buck regulators plus an always-on LDO, all in a compact, low-profile 4mm x 5mm QFN package. The LTC3555's PowerPath control feature seamlessly manages power flow between an AC wall adapter or USB port, Li-Ion battery and system load while its instant-ON operation ensures system load power even with a dead or missing battery.

For fast charging, the LTC3555's switching input stage converts nearly all of the 2.5W available from the USB port to charging current, enabling up to 700mA from a 500mA limited USB supply and up to 1.5A when wall powered. An internal 180milliOhm ideal diode plus optional external ideal diode controller provide a low loss power path, further minimizing heat generation and maximizing efficiency.

The LTC3555's three integrated synchronous buck regulators feature 100% duty cycle operation and are capable of delivering output currents of 1A/400mA/400mA, respectively, with adjustable output voltages down to 0.8V. The internal low RDS(ON) switches enable efficiency as high as 94%, maximizing battery run time. In addition, Burst Mode® operation optimizes efficiency at light loads with a quiescent current of only 35uA per regulator (<1uA in shutdown). The high 2.25MHz switching frequency allows the use 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 LTC3555 features USB-compatible programmable current limiting to 100mA/500mA/1A, while its Bat-Track™ adaptive output control enables high efficiency charging and reduces power dissipation. Standalone autonomous operation simplifies design, eliminating the need for an external microprocessor for charge termination. To preserve battery energy, the LTC3555 draws <23uA from the battery in suspend mode. The charger is compatible with inputs up to 5.5V (7V absolute maximum transient for added robustness).

The LTC3555 is available from stock in a compact, low-profile (0.75mm) 4mm x 5mm QFN-28 package. Pricing starts at $4.65 each for 1,000-piece quantities.