Power conversion to supply micropower applications and the Internet of Things

January 31, 2014 // By Dave Salerno, Linear Technology
The proliferation of wireless sensors supporting the “Internet of Things” has increased the need for small, efficient power converters tailored to untethered low power devices. Application scenarios, that would have appeared infeasible only a short time ago, include deriving full operating power from energy sources as scant as indoor lighting. Such applications typically feature low duty cycles and therefore require some form of energy storage; there are power-supply architectural choices to be made, even at this low level, to ensure the optimum combination of efficiency and availability of the end-product.

The proliferation of wireless sensors supporting the “Internet of Things” has increased the need for small, efficient power converters tailored to untethered low power devices. Application scenarios, that would have appeared infeasible only a short time ago, include deriving full operating power from energy sources as scant as indoor lighting. Such applications typically feature low duty cycles and therefore require some form of energy storage; there are power-supply architectural choices to be made, even at this low level, to ensure the optimum combination of efficiency and availability of the end-product.

A generation of specifically-designed power conversion ICs is emerging to satisfy this need. For example, LTC3129 and LTC3129-1 are monolithic buck-boost DC/DC converters with an input voltage range of 2.42V to 15V. The LTC3129 has an output voltage range of 1.4V to 15.75V, while the LTC3129-1 offers eight pin-selectable fixed output voltages between 1.8V and 15V. Both parts can supply a minimum output current of 200 mA in buck (step-down) mode.

Low power sensors can take advantage of the feature that both parts use zero current when disabled (on both V IN and V OUT), and a quiescent current on V IN of 1.3 µA when the power-saving Burst Mode operation is selected, suiting them to micropower and energy harvesting applications, where high efficiency at extremely light loads is crucial. A buck-boost architecture adds the capability to draw power from a variety of power sources.

Other key features include a fixed 1.2-MHz operating frequency, current mode control, internal loop compensation, automatic Burst Mode operation or low noise PWM mode, an accurate RUN pin threshold to allow the UVLO threshold to be programmed, a power -ood output and an MPPC (maximum power point control) function for optimising power transfer when operating from photovoltaic cells.

A 3 × 3 mm QFN package and high level of integration ease placement into space-constrained applications. Only a few external components and an inductor, which