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ADXL105 Datasheet(PDF) 6 Page - Analog Devices |
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ADXL105 Datasheet(HTML) 6 Page - Analog Devices |
6 / 8 page REV. A ADXL105 –6– THEORY OF OPERATION The ADXL105 is a complete acceleration measurement system on a single monolithic IC. It contains a polysilicon surface- micromachined sensor and BiMOS signal conditioning circuitry to implement an open loop acceleration measurement architec- ture. The ADXL105 is capable of measuring both positive and negative accelerations to a maximum level of ±5 g. The acceler- ometer also measures static acceleration such as gravity, allow- ing it to be used as a tilt sensor. The sensor is a surface micromachined polysilicon structure built on top of the silicon wafer. Polysilicon springs suspend the structure over the surface of the wafer and provide a resistance against acceleration-induced forces. Deflection of the structure is measured with a differential capacitor structure that consists of two independent fixed plates and a central plate attached to the moving mass. A 180 ° out-of-phase square wave drives the fixed plates. An acceleration causing the beam to deflect, will unbalance the differential capacitor resulting in an output square wave whose amplitude is proportional to acceleration. Phase sensi- tive demodulation techniques are then used to rectify the signal and determine the direction of the acceleration. An uncommitted amplifier is supplied for setting the output scale factor, filtering and other analog signal processing. A ratiometric voltage output temperature sensor measures the exact die temperature and can be used for optional calibration of the accelerometer over temperature. VDD The ADXL105 has two power supply (VDD) pins, 13 and 14. The two pins should be connected directly together. The output of the ADXL105 is ratiometric to the power supply. Therefore a 0.22 µF decoupling capacitor between V DD and COM is re- quired to reduce power supply noise. To further reduce noise, insert a resistor (and/or a ferrite bead) in series with the VDD pin. See the EMC and Electrical Noise section for more details. COM The ADXL105 has two common (COM) pins, 4 and 7. These two pins should be connected directly together and Pin 7 grounded. ST The ST pin (Pin 6) controls the self-test feature. When this pin is set to VDD, an electrostatic force is exerted on the beam of the accelerometer causing the beam to move. The change in output resulting from movement of the beam allows the user to test for mechanical and electrical functionality. This pin may be left open-circuit or connected to common in normal use. The self- test input is CMOS and TTL compatible. AOUT The accelerometer output (Pin 8) is set to a nominal scale fac- tor of 250 mV/g (for VDD = 5 V). Note that AOUT is guaranteed to source/sink a minimum of 50 µA (approximately 50 kΩ out- put impedance). So a buffer may be required between AOUT and some A-to-D converter inputs. VMID VMID is nominally VDD/2. It is primarily intended for use as a reference output for the on board uncommitted amplifier (UCA) as shown in Figures 14a and 14b. Its output impedance is ap- proximately 10 k Ω. VDD TOUT ST COM AOUT VMID VIN VNIN UCAOUT UNCOMMITTED AMPLIFIER ADXL105 X SENSOR TEMP SENSOR OUTPUT VDD R1 R2 +V COM 0.22 F GAIN 1 2 3 4 250 500 750 1000 50k 50k 50k 50k 50k 100k 150k 200k SCALE – mV/ g R1 R2 a. Using the UCA to Change the Scale Factor VDD TOUT ST COM AOUT VMID VIN VNIN UCAOUT UNCOMMITTED AMPLIFIER ADXL105 X SENSOR TEMP SENSOR OUTPUT VDD R1 R2 +V COM 0.22 F +V 10k R3 R3 = 5R1 R1 > 20k SCALE = (250) R2 R1 mV/ g b. Using the UCA to Change the Scale Factor and Zero g Bias Figure 14. Application Circuit for Increasing Scale Factor TOUT The temperature sensor output is nominally 2.5 V at +25 °C and typically changes 8 mV/ °C, and is optimized for repeatability rather than accuracy. The output is ratiometric with supply voltage. Uncommitted Amplifier (UCA) The uncommitted amplifier has a low noise, low drift bipolar front end design. The UCA can be used to change the scale factor of the ADXL105 as shown in Figure 14. The UCA may also be used to add a 1- or 2-pole active filter as shown in Fig- ures 15a through 15d. |
Similar Part No. - ADXL105_15 |
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Similar Description - ADXL105_15 |
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