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FEATURES iMEMS(R) Single Chip IC Accelerometer 40 Milli-g Resolution Low Power 2 mA 400 Hz Bandwidth +5.0 V Single Supply Operation 2000 g Shock Survival APPLICATIONS Shock and Vibration Measurement Machine Health Shipping Recorders Military Fuze, Safe and Arm
Low Cost 100 g Single Axis Accelerometer with Analog Output ADXL190*
FUNCTIONAL BLOCK DIAGRAM
TP (DO NOT CONNECT) +VS 2 5k DEMODULATOR CLOCK
9
+VS 0.1 F
ADXL190
GAIN AMP SENSOR
VOUT BUFFER AMP
25k
SELF-TEST
COM
ZERO g ADJUST
GENERAL DESCRIPTION
The ADXL190 is a complete acceleration measurement system on a single monolithic IC. It contains a polysilicon surfacemicromachined sensor and signal conditioning circuitry to implement an open-loop acceleration measurement architecture. The ADXL190 is capable of measuring both positive and negative accelerations up to 100 g, making it suitable for shock and vibration measurement. Typical noise floor is 4 mg/Hz allowing signals below 40 milli-g to be resolved. The ADXL190 can measure both dynamic accelerations, (typical of vibration) or static accelerations, (such as inertial force or gravity). The ADXL190 has a two-pole Bessel switched-capacitor filter. Bessel filters, sometimes called linear phase filters, have a step response with minimal overshoot and a maximally flat group
delay. The -3 dB frequency of the poles is preset at the factory to 400 Hz. These filters are also completely self-contained and buffered, requiring no external components. The product features a built-in self-test feature that exercises both the mechanical structure and electrical circuitry. When triggered by a logic high on the self-test pin, an electrostatic force acts on the beam equivalent to approximately 20% of fullscale acceleration input, and thus a proportional voltage change appears on the output pin. No external components other than a decoupling capacitor are required. The ADXL190 is available in a hermetic 14-lead surface mount cerpak, specified over the -40C to +105C temperature range.
*Patent Pending.
iMEMS is a registered trademark of Analog Devices, Inc.
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Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 (c) Analog Devices, Inc., 1999
ADXL190-SPECIFICATIONS (T = T
A
MIN
to TMAX, VS = +5 V, Acceleration = 0 g unless otherwise noted)
Min ADXL190WQC Typ Max Units
Parameter
Conditions
SENSOR INPUT Dynamic Range1, 2, 3 Alignment Error Nonlinearity Cross Axis Sensitivity SENSITIVITY Initial4 Temperature Drift5 ZERO g BIAS LEVEL Initial2, 3 0 g Offset vs. Temperature5 Zero g Adjustment Gain Zero g Adjust Pin Input Impedance NOISE PERFORMANCE Noise Density FREQUENCY RESPONSE 3 dB Bandwidth Sensor Resonant Frequency SELF-TEST Output Change6 Logic "1" Voltage Logic "0" Voltage Input Impedance ANALOG OUTPUT Output Voltage Range Capacitive Load Drive POWER SUPPLY Specified Performance Quiescent Supply Current TEMPERATURE RANGE Specified Performance
Without Zero-g Adjust
105
1 0.2 2 18.0 0.5 2.5 1.0 0.50 30 4 19.5
g Degrees % % mV/g % V g VOUT/V 0 g Adjust k mg/Hz rms Hz kHz 990 1.0 mV V V k V pF V mA C
Ratiometric from +25C Ratiometric from +25C
16.5
2.3 0.45 20
2.7 0.55 40 12
360
400 24
450 3.5 50 IOUT = 100 A 0.25 1000 4.75 2.0 -40
VS - 0.25
5.25 5.0 +105
NOTES 1 Product is tested at 50 g, and the combination of 0-g error, sensitivity error, and output voltage swing measurements provide the calculations for dynamic range. 2 0-g is nominally VS/2. Use of the 0-g adjustment pin is used to null the 0-g error, resulting in increased dynamic range. It can also be used to create an asymmetrical dynamic range if so desired. 3 The output response is ratiometric and is described by the following equation. V OUT (accel, VS) = [VS/2 (a VS/5 V)] + [(accel) (b V S + c VS 2)(1 0.08)] Where a = 0.2 V, b = 2.712 x 10-3 1/g , c = 0.178 x 10-3 1/g/V. 4 Measured at 100 Hz, 50 g. 5 Specification refers to the maximum change in parameter from its initial value at +25 C to its worst case value at T MIN or TMAX. 6 ST pin Logic "0" to "1"; VOUT = (VOUT @ 5 V) x (VS/5 V). All min and max specifications are guaranteed. Typical specifications are not tested or guaranteed. Specifications subject to change without notice.
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ADXL190
ABSOLUTE MAXIMUM RATINGS* PIN CONFIGURATION
Acceleration (Any Axis, Unpowered for 0.5 ms) . . . . . . 2000 g Acceleration (Any Axis, Powered for 0.5 ms) . . . . . . . . 1000 g +VS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 V to +7.0 V Short Circuit Duration (Any Pin to Common) . . . . Indefinite Operating Temperature . . . . . . . . . . . . . . . . -55C to +125C Storage Temperature . . . . . . . . . . . . . . . . . . -65C to +150C
*Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; the functional operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
NC NC NC NC TEST POINT (DO NOT CONNECT) NC COMMON
1 2 3 4 5 6 7
14 13
VS VS NC NC VOUT SELF-TEST ZERO g ADJUST
ADXL190
12
TOP VIEW 11 (Not to Scale)
10 9 8
NC = NO CONNECT
Drops onto hard surfaces can cause shocks of greater than 2000 g and exceed the absolute maximum rating of the device. Care should be exercised in handling to avoid damage.
PIN FUNCTION DESCRIPTIONS
Figure 1 shows the response of the ADXL190 to the earth's gravitational field. The output values shown are nominal. They are presented to show the user what type of response to expect from each of the output pins due to changes in orientation with respect to the earth.
PIN 1
7 1
Pin No. 1, 2, 3, 4, 6, 11, 12 5 7 8 9 10 13, 14
Function No Connect Test Point (Do Not Connect) Common Zero g Adjust Self-Test VOUT VS
PIN 1
1 14
8
14 7 8
TYPICAL OUTPUT AT PIN 10 = 2.500V
TYPICAL OUTPUT AT PIN 10 = 2.482V
8 7
14
8
1g
1 7
PACKAGE CHARACTERISTICS
14
1
Package 14-Lead Cerpak
JA
JC
Device Weight 5 Grams
PIN 1 TYPICAL OUTPUT AT PIN 10 = 2.500V
PIN 1 TYPICAL OUTPUT AT PIN 10 = 2.518V
+110C/W
+30C/W
EARTH'S SURFACE
Figure 1. ADXL190 Response Due to Gravity
ORDERING GUIDE
Model ADXL190WQC # Axis 1 Specified Voltage +5 V Temperature Range -40C to +105C Package Description 14-Lead Cerpak Package Option QC-14
CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the ADXL190 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
WARNING!
ESD SENSITIVE DEVICE
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ADXL190
APPLICATIONS
All the circuitry needed to drive the sensor and convert the capacitance change to voltage is incorporated on-chip requiring no external components except for standard power supply decoupling. Both sensitivity and the zero-g value are ratiometric to the supply voltage, so that ratiometric devices following the accelerometer (such as an ADC, etc.) will track the accelerometer if the supply voltage changes. The output voltage (VOUT) is a function of both the acceleration input (a) and the power supply voltage (VS) as follows: VOUT = VS/2 - (Sensitivity x VS/5 V x a)
Adjusting the 0 g Bias Level
Table I. Offsets Produced Using the Circuit in Figure 3 for V S =5V
P1 Three-State Three-State 0 0 Three-State 1 1
P0 Three-State 0 Three-State 0 1 Three-State 1
Offset Voltage Produced 0 mV -71 mV -134 mV -191 mV 71 mV 134 mV 191 mV
Offset in g 0 -4 -7.4 -10.6 4 7.4 10.6
In some cases the user may have an asymmetrical input or may want to fine adjust the zero-g output level to obtain maximum dynamic range. The zero-g level is adjusted by supplying a voltage to the zero-g adjustment pin (see Figure 2).
+VS 2 5k
ADXL190
ACCELERATION SIGNAL
GAIN = 3 FILTER VOUT
Another way to adjust the zero g offset is to supply a voltage to the ZERO g ADJUST pin. The difference between VS/2 and the voltage at the ZERO g ADJUST pin is reduced by a factor of 6 (as a result of the internal 5 k and 25 k voltage divider) and then multiplied by a factor of 3 in the output stage of the ADXL190 resulting in a total gain of 0.5. Offset is thus described by the following equation: Offset (V) = (Voltage at the ZERO g ADJUST Pin - VS/2)/2 This voltage may be produced by a variety of methods including a PWM signal from a microcontroller. Care must be taken that the output impedance of this voltage source is less than 5 k and that there is very little ripple (noise). Any noise at the ZERO g ADJUST pin will cause output errors. If an asymmetric range of acceleration is required (e.g., +75 g to -125 g) a resistor may be connected between the ZERO g ADJUST and ground or VS as described above. For example: For a range of +75 g to -125 g the offset required is -25 g. -25 g at 18 mV/g = 450 mV of offset is required. Rearranging the offset equations above: R = [(7.5 x VS)/offset] -30 = 53.3 k connected to ground. For asymmetric operation the g range midpoint may be shifted up to 80 g typically.
250k P1 MICROCONTROLLER P0 500k ZERO g ADJUST
25k ZERO g ADJUST 200k +VS
C2 0.1 F
Figure 2. Optional Zero-g Adjust Circuit Detail
Any voltage difference between the zero-g adjustment pin and VS/2 is reduced by a factor of 6 by the internal resistor divider. This is then gained by the factor of 3 in the output stage for a total gain of 0.5 for the zero-g adjustment. (Note: The ratio of the resistors in the divider is consistent from part-to-part; however, the absolute values can have a 30% tolerance). The zero-g adjustment voltage can be set up by a variety of methods including a potentiometer (as shown in Figure 2), a PWM signal, or with a simple three-state output. The simplest way is by adding a resistor between the ZERO g ADJUST pin and VS or ground. The output will be offset by: Offset (V) = (7.5 x VS)/(30 + R) where R is in k and connected to VS. Offset (V) = (-7.5 x VS)/(30 + R) where R is in k and connected to ground. Resistors may also be connected to microcontroller I/O pins as shown in Figure 3. Using two I/Os that may be set to VS, ground, or three-state, there are seven possibilities as shown in Table I (one cannot set one I/O pin to VS and the other to ground). Using such a system, any ADXL190 may be user trimmed to output 2.5 V 35 mV at zero g.
ADXL190
Figure 3. An Offset Adjustment Scheme
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ADXL190
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
14-Lead Cerpak (QC-14)
0.485 (12.319) MAX
14 8
0.291 (7.391) 0.285 (7.239)
1 7
0.419 (10.643) 0.394 (10.008) 0.345 (8.763) 0.290 (7.366) 0.215 (5.461) 0.119 (3.023) 0.050 0.020 (0.508) (1.27) 0.013 (0.330) BSC SEATING PLANE 0.013 (0.318) 0.009 (0.229)
PIN 1 0.195 (4.953) 0.115 (2.921) 0.020 (0.508) 0.004 (0.102)
0.300 (7.62)
8 0 0.050 (1.270) 0.016 (0.406)
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PRINTED IN U.S.A.
C3457-8-2/99

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