Voltage up-converter for tiny energy-harvesting sources

EDN Europe, 01 Dec 2009

LTC3108 is an integrated step-up DC/DC converter that Linear Technology designed to start-up and run from extremely low input voltage sources such as thermoelectric generators (TEGs), thermopiles and small solar cells. Its self-resonant topology steps up from input voltages as low as 20mV. It can help designers exploit energy sources such as small temperature differentials, generating a flow of electrical energy at very low level that circuits can store in a battery or capacitor, to power low-duty-cycle applications for periodic pulses of operation.

The chip requires a small, standard, external step-up transformer to provide a complete power management solution. Its 2.2V LDO (low drop-out linear regulator) can power an external microcontroller, while its main output is pin selectable to one of four (2.35V, 3.3V, 4.1V or 5V) fixed voltages to power a wireless transmitter or sensors. It provides a power-good indication for a host controller. A second switched output can be enabled by the host in order to power devices that do not have a micropower shutdown capability. The addition of a storage capacitor provides continuous power when the input energy source is unavailable. The LTC3108 has a quiescent current of under 6µA which, together with high efficiency, minimises charge times for the output reservoir capacitor. The device comes in a 3mm x 4mm DFN package (LTC3108EDE) or SSOP-16 (LTC3108EGN); together with very small external components, a low-board-area solution for energy harvesting applications is possible.
Pricing starts at $2.95 each (1,000); industrial temperature grade versions, the LTC3108IDE and LTC3108IGN, cost from $3.45 each.