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EETE SEP 2015

Harwin Shield Clips EETimes Europe Sept 15.qxd:Lay Fig. 4: Application load profile for the schematic in Figure 2. For this application the load is a low power RF device and its load profile is shown in Figure 4. The regions of operation, output and power losses are tabulated and the peak levels are defined for each as shown in Table 2. The total average LTC3106 operating power loss for the load profile is 37μW. The resister divider load adds an additional 5μW of input power loss for a total input power requirement of 207μW. The calculated average efficiency, including the resistive divider is η = 165μW/207μW which is 80%. The available power from the AM-1816 at 200lux is about 400μW. With a converter efficiency of about 80%, the 400μW powers the total 207μW average load with some margin, drawing no power from the battery. If the light conditions become less favorable, the available input power may drop below that needed to maintain the output voltage. The LTC3106 will then operate in “hiccup” mode turning on as VIN increases above 4.2V and turning off if VIN drops below 3.8V. With VIN off, power is then taken from VSTORE (primary battery) until VIN recovers and increases above the 4.2V threshold. If the light conditions become more favorable, VIN will rise to the open-circuit voltage of the harvested source and once again provide all of the load power. Conclusion Even though some energy harvesting sources only provide low levels of useable power, as shown in the design example in this article with a solar cell the size of a business card, they are usually enough to power most wireless sensors. The LTC3106 buck-boost DC/DC converter is optimized for multiple input sources commonly found in low power systems, and provides the necessary feature set for a broad range energy harvesting applications. As a result, the designers of energy harvesting systems, such as WSNs now have useful and appropriate power conversion ICs to greatly simplify the design task. EZ-Shield Clips - Surface Mount EMI/RFI shield clips - Eliminates the need for post reflow operations - Allows easy shield placement and removal - Now available in 10 different sizes P I C K & P L A C E R E A D Y B Y D E S I G N For technical specifications go to: www.harwin.com/ shield-clips www.electronics-eetimes.com Electronic Engineering Times Europe September 2015 33


EETE SEP 2015
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