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ADXL312 bảng dữ liệu(PDF) 10 Page - Analog Devices |
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ADXL312 bảng dữ liệu(HTML) 10 Page - Analog Devices |
10 / 32 page ADXL312 Rev. 0 | Page 10 of 32 THEORY OF OPERATION The ADXL312 is a complete 3-axis acceleration measurement system with a selectable measurement range of ±1.5 g, ±3 g, ±6 g, or ±12 g. It measures both dynamic acceleration resulting from motion or shock and static acceleration, such as gravity, which allows it to be used as a tilt sensor. The sensor is a polysilicon surface-micromachined structure built on top of a silicon wafer. Polysilicon springs suspend the structure over the surface of the wafer and provide a resistance against acceleration forces. Deflection of the structure is measured using differential capacitors that consist of independent fixed plates and plates attached to the moving mass. Acceleration deflects the beam and unbalances the differential capacitor, resulting in a sensor output whose amplitude is proportional to acceleration. Phase- sensitive demodulation is used to determine the magnitude and polarity of the acceleration. POWER SEQUENCING Power can be applied to VS or VDD I/O in any sequence without damaging the ADXL312. All possible power-on modes are summarized in Table 5. The interface voltage level is set with the interface supply voltage, VDD I/O, which must be present to ensure that the ADXL312 does not create a conflict on the communication bus. For single-supply operation, VDD I/O can be the same as the main supply, VS. In a dual-supply application, however, VDD I/O can differ from VS to accommodate the desired interface voltage, as long as VS is greater than or equal to VDDI/O. After VS is applied, the device enters standby mode, where power consumption is minimized and the device waits for VDD I/O to be applied and for the command to enter measurement mode to be received. (This command can be initiated by setting the measure bit in the POWER_CTL register (Address 0x2D).) In addition, any register can be written to or read from to configure the part while the device is in standby mode. It is recommended to configure the device in standby mode and then to enable measurement mode. Clearing the measure bit returns the device to the standby mode. Table 5. Power Sequencing Condition VS VDDI/O Description Power Off Off Off The device is completely off, but there is a potential for a communication bus conflict. Bus Disabled On Off The device is on in standby mode, but communication is unavailable and will create a conflict on the communication bus. The duration of this state should be minimized during power-up to prevent a conflict. Bus Enabled Off On No functions are available, but the device will not create a conflict on the communication bus. Standby or Measurement On On The device is in standby mode, awaiting a command to enter measurement mode, and all sensor functions are off. After the device is instructed to enter measurement mode, all sensor functions are available. POWER SAVINGS Power Modes The ADXL312 automatically modulates its power consumption in proportion to its output data rate, as outlined in Table 6. If additional power savings is desired, a lower power mode is available. In this mode, the internal sampling rate is reduced, allowing for power savings in the 12.5 Hz to 400 Hz data rate range at the expense of slightly greater noise. To enter low power mode, set the LOW_POWER bit (Bit 4) in the BW_RATE register (Address 0x2C). The current consumption in low power mode is shown in Table 7 for cases where there is an advantage to using low power mode. Use of low power mode for a data rate not shown in Table 7 does not provide any advantage over the same data rate in normal power mode. Therefore, it is recommended that only data rates shown in Table 7 be used in low power mode. The current consumption values shown in Table 6 and Table 7 are for a VS of 3.3 V. |
Số phần tương tự - ADXL312 |
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Mô tả tương tự - ADXL312 |
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