USB power manager integrates three buck regulators

Gina Roos

eeProductCenter (07/05/2007 6:56 PM ET)

Milpitas, Calif. — Linear Technology Corp. has released 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 4 x 4-mm QFN package.

The PowerPath manager is said to seamlessly manage the transition between multiple input sources and power to the load, and for fast charging the linear battery charger delivers up to 1.5-A charge current from a wall adapter supply or up to 500-mA charge current from a USB port.

The LTC3557 device's three integrated synchronous buck regulators feature 100% duty cycle operation and are capable of delivering output currents of 600/400/400 mA respectively, with adjustable output voltages down to 0.8 V. The high 2.25-MHz switching frequency allows the use of tiny low-cost capacitors and inductors less than 1 mm 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 35 uA per regulator (<1 uA in shutdown). The regulators are stable with ceramic output capacitors, achieving very low output voltage ripple, said Linear.

The LTC3557's standalone autonomous operation simplifies design, eliminating the need for an external microprocessor for charge termination, said Linear. To preserve battery energy, the IC draws <6 uA from the battery in suspend mode. The power management device 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 5.5 V (7 V absolute maximum transient for added robustness). The internal 200 mOhm ideal diode plus optional external ideal diode controller provide a low loss power path when input current is limited or unavailable, which is said to maximize thermal performance.

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

Linear Technology Corp., 1-408-432-1900, www.linear.com