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basics - Application Note AN017 Low Power Systems Using the...

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Application Note AN017 SWRA074 Page 1 of 11 Low Power Systems Using the CC1010 By K. H. Torvmark Keywords CC1010 Low-power Remote Keyless Entry (RKE) Polling receiver Clock modes Power modes Introduction This application note considers the development of low-power RF systems. It focuses on the CC1010 integrated RF transceiver and microcontroller, and describes several ways of minimizing the current consumption in designs using the CC1010. The various power modes and clock modes of the CC1010 are also described in more detail. Several examples are presented; these include wake-up on button press, wake-up at intervals as well as an RKE (Remote Keyless Entry) application. An Excel spreadsheet for performing battery lifetime calculations is described, and can be downloaded from Chipcon’s web site.
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Application Note AN017 SWRA074 Page 2 of 11 Low-power basics Low power consumption is a very important requirement for battery-operated systems. Having a low current consumption translates directly into long battery lifetime. Several approaches can be used to lower power consumption. Operation frequency is an important parameter. In CMOS circuits, power consumption generally scales linearly with the operating frequency. Therefore, it is important not to use a higher operation frequency than necessary for the application. Perhaps the most important concept is duty-cycle. ICs implementing power-saving modes can be switched between active and power-saving modes to save power. The average current consumption will depend on the ratio between the time spent in active mode and the time spent in the power-saving mode. Above all, when designing for low power consumption, a designer should take a system approach. Low power consumption should be considered in all phases of design. Early on, it is useful to do quick power calculations to see what approaches are feasible. Battery selection is often a very important factor in a design, and will decide the power consumption requirements. Low-power features of the CC1010 By using the CC1010, you already have a head start to get low current consumption because of the integrated very-low-power RF transceiver. The CC1010 MCU core also includes numerous power-saving features. Because of the many combinations possible, we will consider the MCU core and the RF transceiver power consumption separately. The only exception is for power-down mode, where both the RF transceiver and the MCU are shut off. Active, Idle and Power-down modes refer to the MCU. The RF transceiver part is either in RX mode, TX mode or it is turned off. Clock modes The CC1010 is equipped with two crystal oscillators; a high-frequency oscillator that can be used with crystals with frequencies between 3 and 24 MHz, and a low-frequency oscillator designed for use with a 32 kHz watch crystal. The CC1010 can be switched between these two clock sources by writing to the CMODE bit in the X32CON register. Running on the 32 kHz oscillator is called clock mode 1, running on the high-speed oscillator is called clock mode 0. Both oscillators must be powered up and have stabilised before switching between
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