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Monolithic Linear USB Battery Charger with High Efficiency Buck-Boost & Buck Converters

Linear Technology Corporation announces the LTC3558, an efficient, multi-function power management solution for handheld applications.

The LTC3558 integrates a stand-alone Li-Ion/Polymer battery charger and two high efficiency synchronous regulators - one buck-boost and one buck - and 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 stand-alone 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 2.7V to 4.2V while delivering output currents up to 400mA each.

The LTC3558’s integrated synchronous buck regulator features 100% 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%, maximizing battery run time. In addition, Burst Mode® operation optimizes efficiency at light loads with a quiescent current of only 20uA for the buck-boost and 35uA for the buck (<1uA 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%/100% full-scale charge current setting, a SUSP pin for shutdown/enable, and 4 different indication states on the /CHRG pin. The final battery float voltage is accurate to ±0.5%. 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 <3uA from the battery in suspend mode. The charger is compatible with inputs up to 5.5V (7V absolute maximum transient for added robustness).


Multi-Function Linear Charger + Sync Buck-Boost + Sync Buck

Summary of Features: LTC3558
Complete Multi-Function PMIC: Linear Charger,
Synchronous Buck-Boost & Buck Regulators
Battery Charger
Charge Current Programmable up to 950mA from Wall
Adapter Input
Charges Directly from a USB Port with 20%/100%
Current Select
No External MOSFET, Sense Resistor or Blocking
Diodes Needed
Thermal Regulation Maximizes Charging Rate without
Preset Battery Float Voltage with ±0.5% Accuracy
Standalone Autonomous Operation
Charge Status Output with Multiple Indication States
Switching Regulators
High Efficiency Synchronous Regulators: One
Buck-Boost and One Buck
Adjustable Output Voltage Range: Buck-Boost - 2.75V -
5.45V, Buck - Down to 0.8V
Switching Regulator Output Currents: 400mA each
2.25MHz Constant Frequency Operation
Thermally-Enhanced, Low Profile (0.75mm) 20-Lead
3mm x 3mm QFN Package



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