POWER AND LINEAR IC SOLUTIONS

Buck-Boost Controller Extends Battery Life in Handheld Devices

Linear Technology Corporation’s LTC3785 DC/DC controller is designed to answer the challenge of providing a highly efficient 3.3V rail in a single-cell Li-ion powered handheld device. Requiring a minimal number of tiny external components, it generates a fixed output voltage from an input voltage that can be above, below or equal to the output.

For portable power applications to take advantage of the small size and high energy density of modern battery technology, the DC/DC converter powering the sub-circuits and digital LSI must operate efficiently over the full battery discharge and recharge voltage range. This presents a design challenge for Li-ion (2.7V to 4.2V) and Li-Polymer powered systems requiring a 3.3V bus, especially when the 3.3V bus needs to supply currents from 0.5A to 10A. Neither step-down nor step-up converters can efficiently fill this gap.


Simplified Buck-Boost LTC3785 Schematic

The LTC3785 is a synchronous buck-boost switching device that can operate with both input and output voltages between 2.7V to 10V, making it an excellent choice for one or two Li-ion or Li-Polymer cells, or multiple cell NiMH, NiCad or alkaline batteries and higher input charge voltages. This highly integrated controller offers many programmable features including soft start, switching frequency, and the current limit threshold voltage.

The LTC3785 also features an extremely low quiescent current to extend battery life and can be configured to operate in Burst Mode® operation, drawing less than 100µA during standby or idle mode. It is an excellent choice for designers needing a medium power DC/DC converter for tablet PCs, handheld and portable medical instruments, and a wide variety of single- or dual-cell Li-ion or multi-cell alkaline/NiMH powered devices.

A typical configuration that produces a fixed output voltage of 3.3V at 3A from a 2.7V to 10V supply voltage, uses the LTC3785 in a synchronous, four-switch buck-boost DC/DC converter. Its PCB footprint is less than 3cm² (single sided) at a maximum height of 3.2mm and its conversion efficiency is up to 96%.

Features

• Sychronous buck-boost converter
• Single inductor architecture
• 2.7V to 10V input and output range
• Up to 96% efficiency
• Up to 10A output current
• All N-channel MOSFETs: no sense resistor
• True output disconnect during shutdown
• Programmable current limit and soft start
• Optional short-circuit shutdown timer
• Output overvoltage and undervoltage protection
• Programmable frequency: 100kHz to 1MHz
• Selectable burst mode operation
• 24-lead (4mm x 4mm) exposed pad QFN package

Applications

• Single- or dual-cell Li-ion or multi-cell alkaline/NiMH powered devices
• Tablet PCs
• Handheld and portable medical instruments
• Wireless modems
• Mobile telephones

For further information, including a copy of the LTC3785 Datasheet, please click here