Managing portable power

Linear Technology announces the LTC3553, a micropower multifunction power management integrated circuit (PMIC) for portable Li-Ion/Polymer battery-based applications. This makes it ideal for low power portable device applications, including personal navigation devices (PNDs), media players and handheld medical and industrial devices.
The LTC3553 integrates a USB-compatible linear PowerPath manager, a stand-alone battery charger, a high efficiency synchronous buck regulator, a low dropout linear regulator and pushbutton controller in an ultrathin (0.55mm) 3mm x 3mm QFN package. A pin-selectable standby mode reduces battery drain current to just 12A while keeping all outputs in regulation, extending battery run time. The LTC3553 is well suited for low power portable device applications, including personal navigation devices (PNDs), media players and handheld medical and industrial devices.

The LTC3553’s PowerPath manager, with automatic load prioritization, seamlessly manages the transition between multiple input sources to power the load, while delivering up to 400mA battery charge current from a USB port or a 5V wall adapter input. The input current limit is pin-selectable and internally set (no external resistor is required). The LTC3553 is compatible with inputs up to 5.5V (7V maximum transient for added robustness). The device’s ‘instant-on’ operation ensures immediate system load power when USB or a 5V wall supply is available, even with a fully discharged battery. Autonomous operation simplifies design, eliminating the need for an external microprocessor for charge termination. The internal 240mOhm ideal diode provides a low loss power path to the load when input current is limited or unavailable. An NTC function is also available for temperature-qualified charging.

The LTC3553’s integrated synchronous buck regulator delivers up to 200mA output current with a regulated output voltage that is adjustable down to 0.8V. The 1.125MHz switching frequency reduces output ripple while allowing the use of tiny low cost capacitors and inductors less than 1mm in height. Low RDS(ON) internal switches enable buck efficiencies as high as 93%, maximizing battery run time. Buck efficiency is optimized in Burst Mode operation, drawing only 22A of supply current, while standby mode can be used for ‘keep-alive’ applications, reducing the buck’s quiescent current to only 1.5A (<1A in shutdown).
The low dropout (LDO) regulator provides up to 150mA output current. Regulated output voltage is adjustable down to 0.8V, independent of the buck output. The LDO’s power input is accessible as a pin, allowing LDO efficiency to be increased in some applications by powering the LDO from the buck output. Both the buck and LDO are stable with tiny ceramic output capacitors, eliminating the need for larger, expensive tantalum or electrolytic capacitors.

The integrated pushbutton controller enables one-button power up and power down sequencing as well as a status signaling output indicating the button state. The controller also provides a Hard Reset state for software lockup recovery or to enable an ultralow battery drain state (typically 0.2A) for the device.
The LTC3553 is available from stock in a compact, ultralow-profile (0.55mm) 3mm x 3mm UTQFN-20 package. Pricing starts at $2.25 each for 1,000-piece quantities.