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lowpowerZONE Products for the week of November 30, 2009
Linear Technology Says…
LTC3108: 20mV Step-Up Converter & Power Manager for Energy Harvesting Applications
Linear Technology announced the LTC3108, a highly integrated step-up DC/DC converter 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. Small temperature differences can be harvested and used to generate system power instead of traditional battery power. Energy harvesters are designed for applications requiring very low average power, but require periodic pulses of higher load current. For example, in many wireless sensor applications the circuitry is only powered take measurements and transmit data periodically at low duty cycle.
The LTC3108 uses a small standard step-up transformer to provide a complete power management solution. Its 2.2V LDO 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. 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 even when the input energy source is unavailable. The LTC3108’s extremely low quiescent current (<6uA) and high efficiency design ensure the fastest possible charge times for the output reservoir capacitor. The combination of the LT3108’s
EN-Genius Says…
Energy harvesting has been a bit of a fringe activity in our industry. The companies who have been involved up to now have been passionate about the technology but lacking the clout to really make a difference.
Linear has indicated an interest in the technology before, as announced in their last annual report - 2009-09-29 (yes, people other than investors do take notice) ,and there was an earlier part that was a token stab at the technology.
Energy harvesting will find applications where battery technology is inconvenient – mostly because of replacement difficulties – or just downright dangerous. The energy can be sourced from heat waste, solar sourced, or from any other minute movement, light, moisture, strain, motion, or vibration. All these sources can be considered to be free as they are not deliberately generated for harvesting purposes.
The LTC3108 operates from inputs as low as 20 mV, with a proprietary depletion-mode n-channel MOSFET input, and is a dc-dc converter that will normally be used with an external step-up transformer that Linear has identified as a catalog 1:100 Coilcraft part. The outputs are a 2.2 V LDO (probably to power a microprocessor) plus a fixed voltage output that can be set to 2.35 V, 3.3 V, 4.1 V, or 5 V, which could power a transmitter or further sensors. A power good indication is also provided. A reserve energy output is available from a storage capacitor. The switching frequency is determined by the inductance of the transformer secondary winding and will typically be between 20 kHz and 200 kHz. Such low frequencies make the PCB design much simpler than with conventional dc-dc converters.
The quiescent current of the LTC3108 is a minute 6 µA. The part includes a precision micropower reference which activates as soon as the auxiliary voltage exceeds 2 V. At the same time synchronous rectifiers take over the job of rectifying the input voltage, increasing efficiency. The LDO output, main output voltage, power good indication, and stored voltage are all sequenced after the auxiliary feed.
Peltier-powered harvest energy is likely to be the first mainstream application of parts such as the LTC3108. With Linear now in this picture the technology is much more likely to become popular and we should expect to see things speed up considerably particularly for remote sensing transmitters and the like. The early developers of such parts are, unfortunately, going to be left in the dust of Linear’s incredible commercial engine.
The LTC3108 is in production in thermally-enhanced DFN-12 and narrow SSOP-16. It is priced beginning at $2.95 for commercial grades and $3.45 for industrial temperature grades, both in 1000-piece lots.
Data Sheet was not available online at publication.
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