POWER & ENERGY EFFICIENCY HANDBOOK
advanced capacitors enable high-efficiency energy scavenging
modern tantalum capacitors and supercapacitors make it possible for compact energy harvesting systems to power iot mcu applications.
advanced
tantalum capacitors and
supercapacitors are enabling advanced ICs to be powered by compact and low-cost energy harvesting and scavenging sources. These developments make possible maintenance-free control systems in IoT applications extending from remote monitoring to smart industrial point controllers, wearable electronics, and location tracking devices. Consider as a case in point the RE family of Renesas MCUs. It is based on the company’s silicon-onthin-buried-oxide (SOTB) process technology which enables ultra-low power consumption in both active and standby modes. RE family MCUs typically consume 25 µA/ MHz when active in internal lowdropout regulator (LDO) mode, 12 µA/MHz in external dc/dc mode, 400 nA in standby with 32 KB RAM retention, and 100 nA in deep
standby. Low current consumption at low voltages allows these advanced MCUs to employ energy harvesting or scavenging power sources rather than traditional batteries or mains. Each RE01 MCU contains an energy harvesting controller (EHC) equipped with a sub-level PMIC, charge controller, and power management function. These EHCs harvest energy generated from solar, piezoelectric, micro turbine, pressure, and thermal electric generator (TEG) power sources. The MCUs use one of two integrated capacitors to manage, channel, and balance harvested power and MCU power consumption. In this application, the EHCs provide basic functions like reverse-current protection and also act as the direct energy harvesting link. The energy harvesting actions include voltage regulation, quick start-up control, autonomous and reliable startup sequencing, start-up current control, energy storage charge management, and the selection of capacitor power sources. When an RE01 MCU is
ron demcko, daniel west, ashley stanziola • kyocera avx
re01 microcontroller an re01 mcu powered by harvested energy.
powered by harvested energy, an advanced tantalum capacitor provides temporary energy storage while a large-valued supercapacitor handles secondary storage. The ultra-low-power MCUs enabled by these advanced capacitors handle control and communication capabilities in IoT applications ranging from remote environmental monitoring and agricultural optimization to asset tracking, wearable electronics, and set-itand-forget-it industrial monitoring. The EHCs in RE01 MCUs configured for energy harvesting rely on a start-up capacitor (C-SU) to charge quickly and to provide the low-level power for MCU power-up initiation. For long-term power, they can use batteries or advanced supercapacitors. Once energy harvesting power is apparent, the EHC charges the C-SU. When C-SU charges to 3.0 V, power-on reset initiates at the MCU and the secondary supercapacitor starts charging. While the supercapacitor
charges, the EHC uses C-SU power to initiate various MCU operations. Once the supercapacitor has charged, the MCU draws on its energy for longer-term operation. During that time, the C-SU recharges so it can maintain various active computing functions when the EHCs isolate the supercapacitors from the MCU to recharge them. Once the supercapacitors recharge, the MCU again transitions from the C-SU to the supercapacitor power source and, in doing so, enables more of its functions. This process continues in a loop until the energy harvesting power source is no longer available and the system shuts down. At that point, the MCU waits for C-SU to charge and the use cycle continues.
the start-up capacitor
The C-SU in an energy harvesting MCU must operate from -40 to + 85°C and provide 100–150 µF of capacitance across that
the re01 mcu energy harvesting operation pictured here illustrates the power consumption requirements for sotb technology compared to other competing process technologies, such as fully depleted silicon on insulator (fc-soi) processed drives. 20
DESIGN WORLD — EE NETWORK
10 • 2022
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