USB Power Manager Li-Ion/Polymer battery applications

3rd November 2007

ES Admin

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Linear Technology has announced the LTC3557, a multi-function power management solution for Li-Ion/Polymer battery applications. The LTC3557 integrates a linear PowerPath manager, a standalone battery charger, ideal diode, three high efficiency synchronous buck regulators and an always-on LDO in a low-profile 4mm x 4mm QFN package. The powerpath manager seamlessly manages the transition between multiple input sources and power to the load, while for fast charging the linear battery charger delivers up to 1.5A charge current from a wall adapter supply or up to 500mA charge current from a USB port.

The LTC3557's three integrated synchronous buck regulators feature 100% duty cycle operation and are capable of delivering output currents of 600/400/400mA respectively, with adjustable output voltages down to 0.8V. The high 2.25MHz switching frequency allows the use of tiny low cost capacitors and inductors less than 1mm in height. The internal low RDS(ON) switches enable efficiencies as high as 95%, maximizing battery run time. In addition, pin-selectable Burst Mode® operation optimizes efficiency at light loads with a quiescent current of only 35uA per regulator (<1uA in shutdown). Furthermore, the regulators are stable with ceramic output capacitors, achieving very low output voltage ripple.

The LTC3557's standalone autonomous operation simplifies design, eliminating the need for an external microprocessor for charge termination. To preserve battery energy, the IC draws <6uA from the battery in suspend mode. The LTC3557 can control a high-voltage buck regulator to achieve high efficiency Bat-Track™ charging and powerpath control from a high voltage source, reducing power dissipation. The charger is compatible with inputs up to 5.5V (7V absolute maximum transient for added robustness). The internal 200mOhm ideal diode plus optional external ideal diode controller provide a low loss power path when input current is limited or unavailable, maximizing thermal performance.

The LTC3557 is available from stock in a compact, low-profile (0.75mm) 4mm x 4mm QFN-28 package. Pricing starts at $3.95 each for 1,000-piece quantities.