Inertial and wireless sensor allows system wake-up by motion detection
The device provides temperature-compensated and factory calibrated digital measurement values with high resolution via I²C or SPI interface plus wide measurement ranges (±2048°/s and ±8g). For battery powered applications, like the air-mouse, it is essential that the system switches to sleep mode as soon as no more motion is detected. In order to efficiently resume operations after sleep mode, a low- power motion detection function is needed.
The SD746 features a low-power motion detection function where power consumption is drastically reduced by turning off the gyroscopes and operating the accelerometers in a pulsed mode. This new mode of operation reduces power consumption to 25μA at 1Hz accelerometer sample rate. Through the digital interface the user can set a physical g-level which serves as a detection threshold. If the variation of the acceleration detected on the three accelerometers is greater than the threshold set, an ‘interrupt pin’ is activated. This interruption can be used to wake-up the host controller, which in turn brings back the sensor to the normal operation mode. If the power consumption on a higher sleep mode is acceptable, the user can opt for faster accelerometer sampling rates of up to 8 sampling windows per second, with a power consumption of 125μA.
The new SD746 is scaled for an operating voltage of 2.55 through 3.6 V and an operating temperature range of -40 to +85°C. The offset error at room temperature is ±5°/s for the gyroscope signal and ±0.05g for the accelerometer signal. Sensitivity error at room temperature is ±2% for the gyroscope and acceleration signal, respectively. The SD746 also features a special power-off mode in which power consumption is zero while the SPI interface remains at high-impedance levels so that the sensor need not be separated from the bus.
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