ADXL311JE

ADXL311 AD | Alldatasheet

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Technical content

Low Cost, Ultracompact ±2 g Dual-Axis Accelerometer ADXL311

FEATURES

Dual-axis accelerometer on a single IC chip 5 mm × 5 mm × 2 mm CLCC package Low power < 400 µA (typ) X-axis and Y-axis aligned to within 0.1° (typ) BW adjustment with a single capacitor Single-supply operation High shock survival

APPLICATIONS

Tilt and motion sensing in cost-sensitive applications Smart handheld devices Computer security Input devices Pedometers and activity monitors Game controllers Toys and entertainment products GENERAL DESCRIPTION The ADXL311 is a low cost, low power, complete dual-axis accelerometer with signal conditioned voltage outputs, all on a single monolithic IC. The ADXL311 is built using the same proven iMEMS® process used in over 100 million Analog Devices accelerometers shipped to date, with demonstrated 1 FIT reliability (1 failure per 1 billion device operating hours). The ADXL311 will measure acceleration with a full-scale range of ±2 g. The ADXL311 can measure both dynamic acceleration (e.g., vibration) and static acceleration (e.g., gravity). The outputs are analog voltages proportional to acceleration. The typical noise floor is 300 µg/√Hz allowing signals below 2 mg (0.1° of inclination) to be resolved in tilt sensing appli- cations using narrow bandwidths (10 Hz). The user selects the bandwidth of the accelerometer using capacitors CX and CY at the XFILT and YFILT pins. Bandwidths of 1 Hz to 2 kHz may be selected to suit the application. The ADXL311 is available in a 5 mm × 5 mm × 2 mm 8-terminal hermetic CLCC package COM YOUT XOUTVDD CX ADXL311JE Y SENSOR 3.0V SELF TEST X SENSOR RFILT 32kΩ RFILT 32kΩ 200kΩ CY CDC OSCILLATOR DEMOD DEMOD BIAS Figure 1. Functional Block Diagram Information fur nished by An alog Devices is believed t o be accurate an d r eliable. infringements of patents or other rights of third parties that m ay result from its use. registered trademarks are the property of their respective companies. Fax: 781.326.8703 © 2003 Analog Devices, Inc. All rights reserved.

Design Trade-Offs for Selecting Filter Characteristics: The

REVISION HISTORY

7/03—Data sheet changed from Rev. 0 to Rev. A. Revision 0: Initial Version Rev. A | Page 2 of 12

Table 1. TA = 25oC, VDD = 3 V, RBIAS = 125 kΩ, Acceleration = 0 g, unless otherwise noted.) 2 Cross axis sensitivity is the algebraic sum of the alignment and the inherent sensitivity errors. 3 Defined as the output change from ambient to maximum temperature or ambient to minimum temperature.

Table 3. Package Characteristics

The ADXL311 is a complete, dual-axis acceleration measure- ment system on a single monolithic IC. It contains a polysilicon surface-micromachined sensor and signal conditioning cir- cuitry to implement an open-loop acceleration measurement architecture. The output signals are analog voltage proportional to acceleration. The ADXL311 is capable of measuring both positive and negative accelerations to at least ±2 g. The acceler- ometer can measure static acceleration forces, such as gravity, allowing 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 forces. Deflection of the structure is meas- ured using a differential capacitor that consists of independent fixed plates and central plates attached to the moving mass. The fixed plates are driven by 180° out of phase square waves. Accel- eration will deflect the beam and unbalance the differential capacitor, resulting in an output square wave whose amplitude is proportional to acceleration. Phase sensitive demodulation techniques are then used to rectify the signal and determine the direction of the acceleration. The output of the demodulator is amplified and brought off- chip through a 32 kΩ resistor. At this point, the user can set the signal bandwidth of the device by adding a capacitor. This filtering improves measurement resolution and helps prevent aliasing. For most applications, a single 0.1 µF capacitor, CDC, will ade- quately decouple the accelerometer from noise on the power supply. However, in some cases, particularly where noise is pre- sent at the 100 kHz internal clock frequency (or any harmonic thereof), noise on the supply may cause interference on the ADXL311 output. If additional decoupling is needed, a 100 Ω (or smaller) resistor or ferrite beads may be inserted in the sup- ply line of the ADXL311. Additionally, a larger bulk bypass capacitor (in the 1 µF to 4.7 µF range) may be added in parallel to CDC. SETTING THE BANDWIDTH USING CX AND CY The ADXL311 has provisions for bandlimiting the XOUT and YOUT pins. Capacitors must be added at these pins to implement low-pass filtering for antialiasing and noise reduction. The equation for the 3 dB bandwidth is ( ) ()( )YX,dB CF ×π= kΩ322/13– or, more simply () YX,dB CF /F53– µ= The tolerance of the internal resistor (RFILT) can vary typically as much as ±15% of its nominal value of 32 kΩ; thus, the band- width will vary accordingly. A minimum capacitance of 1000 pF for CX and CY is required in all cases. Table 4. Filter Capacitor Selection, CX and CY be left open circuit or connected to common in normal use. noise performance. The value of the resistor used is not critical. the measurement resolution (smallest detectable acceleration). the analog filter bandwidth at XOUT and YOUT. The output of the ADXL311 has a typical bandwidth of 5 kHz.

dynamic range of the accelerometer. Table 5. Estimation of Peak-to-Peak Noise noise output of the ADXL311 for various CX and CY values. Table 6. Filter Capacitor Selection (CX, CY) can be powered with VDD as low as 2.7 V or as high as 5.25 V. VDD = 5 V the output sensitivity is typically 312 mV/g. nominally equal to VDD/2 at all supply voltages. fore, the noise density decreases as the supply voltage increases. approximately equivalent to 800 mg (typical). The supply current increases as the supply voltage increases. Typical current consumption at VDD = 5 V is 600 µA. input vector to determine the orientation of an object in space. 12.2 mg per degree and resolution declines. shock, or other accelerations.

Figure 10. 8-Lead CLCC Table 7. Pin Function Descriptions—8-Lead CLCC

1 ST Self Test

2 BIAS Bias Resistor (≈200 kΩ)

3 COM Common

4 NC Do Not Connect

5 NC Do Not Connect

6 YOUT Y Channel Output

7 XOUT X Channel Output

0.38 DIAMETER

Figure 11. 8-Terminal Ceramic Leadless Chip Carrier [CLCC] degradation or loss of functionality.

Rev. A | Page 11 of 12

Rev. A | Page 12 of 12 NOTES © 2003 Analo g De vices, Inc. All rights reserve d. Tra demarks and registered tra demarks are the proper ty of their respectiv e companies. C03582–0–7/03(A)