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ADXL377BCPZ-RL датащи(PDF) 9 Page - Analog Devices |
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ADXL377BCPZ-RL датащи(HTML) 9 Page - Analog Devices |
9 / 12 page Data Sheet ADXL377 Rev. 0 | Page 9 of 12 APPLICATIONS INFORMATION POWER SUPPLY DECOUPLING For most applications, a single 0.1 µF capacitor, CDC, placed close to the ADXL377 supply pins adequately decouples the accelerometer from noise on the power supply. However, in applications where noise is present at the 50 kHz internal clock frequency (or any harmonic thereof), additional care in power supply bypassing is required because this noise can cause errors in acceleration measurement. If additional decoupling is needed, a 100 Ω (or smaller) resistor or ferrite bead can be inserted in the supply line. In addition, a larger bulk bypass capacitor (1 µF or greater) can be added in parallel to CDC. Ensure that the connection from the ADXL377 ground to the power supply ground is low impedance because noise transmitted through ground has a similar effect as noise transmitted through VS. SETTING THE BANDWIDTH USING CX, CY, AND CZ The ADXL377 has provisions for band-limiting the XOUT, YOUT, and ZOUT pins. A capacitor must be added at each of these pins to implement low-pass filtering for antialiasing and noise reduction. The equation for the −3 dB bandwidth is f−3 dB = 1/(2π × 32 kΩ × Cx) or more simply, f−3 dB = 5 µF/Cx The tolerance of the internal resistor (RFILT) typically varies by as much as ±15% of its nominal value (32 kΩ), and the bandwidth varies accordingly. A minimum capacitance of 1000 pF for CX, CY, and CZ is recommended in all cases. Table 4. Filter Capacitor Selection for CX, CY, and CZ Bandwidth (Hz) Capacitor (µF) 50 0.10 100 0.05 200 0.025 500 0.01 1000 0.005 SELF-TEST The ST pin controls the self-test feature. When this pin is set to VS, an electrostatic force is exerted on the accelerometer beam. The resulting movement of the beam allows the user to test whether the accelerometer is functional. The typical change in output is −1.08 g (corresponding to −6.5 mV) for the x-axis, +1.08 g (or +6.5 mV) for the y-axis, and +1.83 g (or +11.5 mV) for the z-axis. The ST pin can be left open circuit or connected to ground (GND) in normal use. Never expose the ST pin to voltages greater than VS + 0.3 V. If the system design is such that this condition cannot be guaran- teed (for example, if multiple supply voltages are present), it is recommended that a clamping diode with low forward voltage be connected between ST and VS. SELECTING FILTER CHARACTERISTICS: NOISE/BANDWIDTH TRADE-OFF The selected accelerometer bandwidth ultimately determines the measurement resolution (smallest detectable acceleration). Filtering can be used to lower the noise floor, thereby improving the resolution of the accelerometer. Resolution is dependent on the analog filter bandwidth at XOUT, YOUT, and ZOUT. The output of the ADXL377 has a typical bandwidth of 1000 Hz. The user must filter the signal at this point to limit aliasing errors. The analog bandwidth must be no more than half the analog-to- digital sampling frequency to minimize aliasing. The analog bandwidth can be decreased further to reduce noise and improve resolution. The ADXL377 noise has the characteristics of white Gaussian noise, which contributes equally at all frequencies and is described in terms of µg/√Hz (that is, the noise is proportional to the square root of the accelerometer bandwidth). Limit the bandwidth to the lowest frequency required by the application to maximize the resolution and dynamic range of the accelerometer. With the single-pole roll-off characteristic, the typical noise of the ADXL377 is determined by rms Noise = Noise Density × ) 1.6 ( × BW It is often useful to know the peak value of the noise. Peak-to- peak noise can only be estimated by statistical methods. Table 5 can be used to estimate the probability of exceeding various peak values, given the rms value. Table 5. Estimation of Peak-to-Peak Noise Peak-to-Peak Value Percentage of Time That Noise Exceeds Nominal Peak-to-Peak Value (%) 2 × rms 32 4 × rms 4.6 6 × rms 0.27 8 × rms 0.006 |
Аналогичный номер детали - ADXL377BCPZ-RL |
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Аналогичное описание - ADXL377BCPZ-RL |
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