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CBC-EVAL-08 データシート(PDF) 8 Page - List of Unclassifed Manufacturers |
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CBC-EVAL-08 データシート(HTML) 8 Page - List of Unclassifed Manufacturers |
8 / 11 page EnerChip Solar Energy Harvesting Demo Kit ©2009 Cymbet Corporation • Tel: +1-763-633-1780 • www.cymbet.com DS-72-08 Rev15 Page 8 of 11 While it is relatively straightforward to calculate a power budget and design a system to work within the constraints of the power and energy available, it is easy to overlook the power required to initialize the system to a known state and to complete the radio link with the host system or peer nodes in a mesh network. The initialization phase can sometimes take two to three times the power needed for steady state operation. Ideally, the hardware should be in a low power state when the system power-on reset is in its active state. If this is not possible, the microcontroller should place the hardware in a low power state as soon as possible. After this is done, the microcontroller should be put into a sleep state long enough for the energy harvester to replenish the energy storage device. If the power budget is not exceeded during this phase, the system can continue with its initialization. Next, the main initialization of the system, radio links, analog circuits, and so forth, can begin. Care should be taken to ensure that the time the system is on during this phase does not exceed the power budget. Several sleep cycles might be needed to ‘stairstep’ the system up to its main operational state. The Cymbet CBC5300 energy harvester module has a handshake line CHARGE to indicate to the microcontroller when energy is available. Another way to know whether energy is available is to have the microcontroller monitor the voltage on its power bus using one its internal A/D converters. Circuit Recommendations to Save Power In most system power budgets, the peak power required is not as critical as the length of time the power is required. Careful selection of the message protocol for the RF link can have a significant impact on the overall power budget. In many cases, using higher power analog circuits that can be turned on, settle quickly, and be turned off can decrease the overall energy consumed. Microcontroller clock frequency can also have a significant impact on the power budget. In some applications it might be advantageous to use a higher microcontroller clock frequency to reduce the time the microcontroller and peripheral circuits are active. Avoid using circuits that bias microcontroller digital inputs to mid-level voltages; this can cause significant amounts of parasitic currents to flow. Use 10MΩ to 22MΩ pull-up/down resistors where possible. However, be aware that high circuit impedances coupled with parasitic capacitance can make for a slow rise/fall time that can place the voltage on the microcontroller inputs at mid-levels, resulting in parasitic current flow. One solution to the problem is to enable the internal pull-up/down resistor of the microcontroller input to force the input to a known state, then disable the resistor when it’s time to check the state of the line. If using the microcontroller’s internal pull-up/down resistors on the inputs to bias push-button switches in a polled system, leave the pull-up/ down resistor disabled and enable the resistor only while checking the state of the input port. Alternatively, in an interrupt-driven system, disable the pull-up/down resistor within the first few instructions in the interrupt service routine. Enable the pull-up/down resistor only after checking that the switch has been opened. Microcontroller pull-up/down resistors are typically less than 100kΩ and will be a huge load on the system if left on continuously while a button is being pressed or if held for any significant length of time. For even greater reduction in power, use external pull-up/down resistors in the 10MΩ to 22MΩ range. Bias the external resistor not with the power rail but with a microcontroller port. The same algorithm used for internal pull-up/down resistors can then be used to save power. The CHARGE line on the CBC5300 has a 10MΩ pull-up resistor with a very slow rise time. Use an internal microcontroller pull-down resistor to force the CHARGE line low all of the time and then disable the pull-down resistor to check the state of the line. This will keep the CHARGE line from biasing the input at mid level for long periods of time which could case large parasitic currents to flow. The CBC5300 energy harvester module has a feature for disabling the on-board EnerChip thin film batteries. A handshake line BATOFF is provided for use of this feature. A high level will disable the EnerChips. This is useful in very low ambient energy conditions to steer all of the available energy into the load. EnerChip batteries have very low self-discharge rates (typically 2.5% per year) so it is not necessary to continuously charge them. |
同様の部品番号 - CBC-EVAL-08 |
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同様の説明 - CBC-EVAL-08 |
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