AD ADXL105AQC High accuracy 61 g to 65 g single axis imems accelerometer with analog input Datasheet

a
High Accuracy ⴞ1 g to ⴞ5 g Single Axis
iMEMS® Accelerometer with Analog Input
ADXL105*
FEATURES
Monolithic IC Chip
2 mg Resolution
10 kHz Bandwidth
Flat Amplitude Response (ⴞ1%) to 5 kHz
Low Bias and Sensitivity Drift
Low Power 2 mA
Output Ratiometric to Supply
User Scalable g Range
On-Board Temperature Sensor
Uncommitted Amplifier
Surface Mount Package
+2.7 V to +5.25 V Single Supply Operation
1000 g Shock Survival
FUNCTIONAL BLOCK DIAGRAM
VDD
ADXL105
TEMP
SENSOR
TOUT
UNCOMMITTED
AMPLIFIER
ST
X SENSOR
COM
COM
AOUT
VMID VNIN
VIN
UCAOUT
APPLICATIONS
Automotive
Accurate Tilt Sensing with Fast Response
Machine Health and Vibration Measurement
Affordable Inertial Sensing of Velocity and Position
Seismic Sensing
Rotational Acceleration
GENERAL DESCRIPTION
The ADXL105 is a high performance, high accuracy and complete single-axis acceleration measurement system on a single
monolithic IC. The ADXL105 offers significantly increased
bandwidth and reduced noise versus previously available micromachined devices. The ADXL105 measures acceleration with a
full-scale range up to ± 5 g and produces an analog voltage output. Typical noise floor is 225 µg√Hz allowing signals below
2 mg to be resolved. A 10 kHz wide frequency response enables
vibration measurement applications. The product exhibits significant reduction in offset and sensitivity drift over temperature
compared to the ADXL05.
The ADXL105 can measure both dynamic accelerations, (typical of vibration) or static accelerations (such as inertial force,
gravity or tilt).
Output scale factors from 250 mV/g to 1.5 V/g are set using the
on-board uncommitted amplifier and external resistors. The
device features an on-board temperature sensor with an output
of 8 mV/°C for optional temperature compensation of offset vs.
temperature for high accuracy application.
The ADXL105 is available in a hermetic 14-lead surface mount
Cerpak with versions specified for the 0°C to +70°C, and
–40°C to +85°C temperature ranges.
*Patent Pending.
iMEMS is a registered trademark of Analog Devices, Inc.
REV. A
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
© Analog Devices, Inc., 1999
(TA = TMIN to TMAX, TA = +25ⴗC for J Grade Only, VS = +5 V, @ Acceleration = 0 g,
ADXL105–SPECIFICATIONS unless otherwise noted)
Parameter
Conditions
SENSOR INPUT
Measurement Range1
Nonlinearity
Alignment Error2
Cross Axis Sensitivity3
Best Fit Straight Line
SENSITIVITY4 (Ratiometric)
Initial
At AOUT
␣␣␣␣␣␣␣
Min
±5
Z Axis, @ +25°C
225
80
VS = 2.7 V
vs. Temperature5, 6
ZERO g BIAS LEVEL5 (Ratiometric)
Zero g Offset Error
vs. Supply
vs. Temperature5, 7
NOISE PERFORMANCE
Voltage Density7
Noise in 100 Hz Bandwidth
At AOUT
From +2.5 V Nominal
@ +25°C
225
2.25
10
13
From +2.5 V Nominal
Units
±5
g
% of FS
Degrees
%
275
120
mV/g
mV/g
%
+625
+20
mV
mV/VDD/V
mV
325
µg/√Hz
mg rms
12
18
–100
kHz
kHz
+100
mV
mV/°C
kΩ
+15
mV
kΩ
500
mV
kΩ
VS – 0.5
V
pF
+25
mV
µV/°C
V
nA
V/mV
V
pF
8
10
From +2.5 V Nominal
SELF-TEST (Proportional to VDD)
Voltage Delta at AOUT
Input Impedance8
Self-Test “0” to “1”
AOUT
Output Drive
Capacitive Load Drive
I = ± 50 µA
POWER SUPPLY
Operating Voltage Range
Quiescent Supply Current
250
105
± 0.5
Max
50
VMID4 (Ratiometric)
Output Error
Output Impedance
UNCOMMITTED AMPLIFIER
Initial Offset
Initial Offset vs. Temperature
Common-Mode Range
Input Bias Current9
Open Loop Gain
Output Drive
Capacitive Load Drive
±7
0.2
±1
±1
–625
–20
FREQUENCY RESPONSE
3 dB Bandwidth
Sensor Resonant Frequency
TEMP SENSOR4 (Ratiometric)
Output Error at +25°C
Nominal Scale Factor
Output Impedance
ADXL105J/A
Typ
–15
10
100
30
50
0.50
1000
–25
5
1.0
4.0
25
100
I = ± 100 µA
0.25
1000
VS – 0.25
2.70
At 5.0 V
At 2.7 V
1.9
1.3
700
Turn-On Time
TEMPERATURE RANGE
Operating Range J
Specified Performance A
0
–40
5.25
2.6
2.0
V
mA
mA
µs
+70
+85
°C
°C
NOTES
1
Guaranteed by tests of zero g bias, sensitivity and output swing.
2
Alignment of the X axis is with respect to the long edge of the bottom half of the Cerpak package.
3
Cross axis sensitivity is measured with an applied acceleration in the Z axis of the device.
4
This parameter is ratiometric to the supply voltage V DD. Specification is shown with a 5.0 V V DD. To calculate approximate values at another V DD, multiply the specification by
VDD/5 V.
5
Specification refers to the maximum change in parameter from its initial value at +25°C to its worst case value at TMIN to T MAX.
6
See Figure 3.
7
See Figure 2.
8
CMOS and TTL Compatible.
9
UCA input bias current is tested at final test.
All min and max specifications are guaranteed. Typical specifications are not tested or guaranteed.
Specifications subject to change without notice.
–2–
REV. A
ADXL105
ABSOLUTE MAXIMUM RATINGS*
Package Characteristics
Acceleration (Any Axis, Unpowered for 0.5 ms) . . . . . .1000 g
Acceleration (Any Axis, Powered for 0.5 ms) . . . . . . . . . 500 g
+VS ␣ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +7.0 V
Output Short Circuit Duration
␣ ␣ (Any Pin to Common) . . . . . . . . . . . . . . . . . . . . Indefinite
Operating Temperature . . . . . . . . . . . . . . . . –55°C to +125°C
Storage Temperature . . . . . . . . . . . . . . . . . . –65°C to +150°C
Package
␪JA
␪JC
Device Weight
14-Lead Cerpak
110°C/W
30°C/W
<2 Grams
Model
Temperature Range
Package Option
*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.
ADXL105JQC
ADXL105AQC
0°C to +70°C
–40°C to +85°C
QC-14
QC-14
ORDERING GUIDE
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 ADXL105 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
Drops onto hard surfaces can cause shocks of greater than 1000 g
and exceed the absolute maximum rating of the device. Care should
be exercised in handling to avoid damage.
PIN CONFIGURATION
PIN FUNCTION DESCRIPTIONS
VDD
13
VDD
NC 3
12
UCAOUT
ADXL105
VIN
TOP VIEW
(Not to Scale) 10
VNIN
NC 5
COM 4
11
ST 6
9
VMID
7
8
AOUT
COM
NC = NO CONNECT
1
12
13
14
9
2
11
10
4
11
3
12
2
13
1
14
AOUT = 2.75V
3
8
4
9
7
9
10
6
10
11
5
5
12
4
8
13
3
6
14
2
7
1
5
Temperature Sensor Output
No Connect
Common
Self-Test
Common (Substrate)
Accelerometer Output
VDD/2 Reference Voltage
Uncommitted Amp Noninverting Input
Uncommitted Amp Inverting Input
Uncommitted Amp Output
Power Supply Voltage
TOUT
NC
COM
ST
COM
AOUT
VMID
VNIN
VIN
UCAOUT
VDD
14
NC 2
8
1
2, 3, 5
4
6
7
8
9
10
11
12
13, 14
TOUT 1
6
Description
7
Pin No. Name
AOUT = 2.50V
AOUT = 2.25V
Figure 1. ADXL105 Response Due to Gravity
REV. A
–3–
ADXL105 –Typical Performance Characteristics
120
25
90
20
0g OFFSET SHIFT – mV
60
% OF UNITS
30
0
–30
15
10
–60
5
–90
–120
–50
0
50
TEMPERATURE – 8C
0
0.242 0.244 0.246 0.248 0.250 0.252 0.254 0.256 0.258
SENSITIVITY – V/g
100
Figure 2. Typical 0 g Shift vs. Temperature*
0.260
Figure 5. Sensitivity Distribution*
5
2.5
4
CURRENT – mA
SENSITIVITY CHANGE – %
2
3
2
1
1.5
1
0
0.5
–1
–2
–50
0
50
TEMPERATURE – 8C
0
100
2.7
Figure 3. Typical Sensitivity Shift vs. Temperature*
3.3
4
SUPPLY VOLTAGE
5
5.5
Figure 6. Typical Supply Current vs. Supply Voltage
20
18
18
12
16
–6
OUTPUT – dB
% OF UNITS
14
12
10
8
–0
–6
6
4
–12
2
0
–18
100
2.2 2.25 2.3 2.35 2.4 2.45 2.5 2.55 2.6 2.65 2.7 2.75 2.8
OUTPUT – V
Figure 4. 0 g Output Distribution*
1000
10000
FREQUENCY – Hz
100000
Figure 7. Noise Graph
*Data from several characterization lots.
–4–
REV. A
ADXL105
500
450
NOISE – mg / Hz
400
350
300
250
200
150
2
3
4
SUPPLY VOLTAGE
6
5
Figure 8. Typical Noise Density vs. Supply Voltage
Figure 11. Typical Self-Test Response at V DD = 5 V
15
40
35
10
ADXL105 SOLDERED TO PCB
30
OUTPUT – dB
% OF UNITS
5
25
20
15
0
–5
ADXL105 SOLDERED AND GLUED TO PCB
10
–10
5
–15
0
205
210
215
220
225 230
235
NOISE DENSITY – mg / Hz
240
245
1
250
10
100
1000
FREQUENCY – Hz
10000
100000
Figure 12. Frequency Response
Figure 9. Noise Distribution*
20
400
18
300
ADXL105 SOLDERED TO PCB
16
200
PHASE – Degrees
% OF PARTS
14
12
10
8
6
100
0
–100
4
–200
2
–300
1.375
1.125
0.875
0.375
0.625
0.0125
–0.375
–0.0125
–0.625
–0.875
–1.125
ADXL105 SOLDERED AND GLUED TO PCB
–1.375
0
1
10
100
1000
FREQUENCY – Hz
10000
DEGREES OF MISALIGNMENT
Figure 13. Phase Response
Figure 10. Rotational Die Alignment*
*Data from several characterization lots.
REV. A
–5–
100000
ADXL105
THEORY OF OPERATION
VMID
The ADXL105 is a complete acceleration measurement system
on a single monolithic IC. It contains a polysilicon surfacemicromachined sensor and BiMOS signal conditioning circuitry
to implement an open loop acceleration measurement architecture. The ADXL105 is capable of measuring both positive and
negative accelerations to a maximum level of ± 5 g. The accelerometer also measures static acceleration such as gravity, allowing it to be used as a tilt sensor.
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 approximately 10 kΩ.
+V
0.22mF
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 sensitive demodulation techniques are then used to rectify the signal
and determine the direction of the acceleration.
VDD
VDD
ADXL105
TEMP
SENSOR
TOUT
UNCOMMITTED
AMPLIFIER
ST
X SENSOR
COM
AOUT
COM
VNIN VIN
VMID
R1
UCAOUT
R2
OUTPUT
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.
GAIN
SCALE – mV/g
1
2
3
4
250
500
750
1000
R1
R2
50kV
50kV
50kV 100kV
50kV 150kV
50kV 200kV
a. Using the UCA to Change the Scale Factor
VDD
+V
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 VDD and COM is required 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.
0.22mF
VDD
VDD
ADXL105
TEMP
SENSOR
TOUT
UNCOMMITTED
AMPLIFIER
ST
X SENSOR
COM
The ADXL105 has two common (COM) pins, 4 and 7. These
two pins should be connected directly together and Pin 7
grounded.
COM
COM
AOUT
VNIN VIN
VMID
R1
ST
UCAOUT
R2
OUTPUT
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 selftest input is CMOS and TTL compatible.
+V
R3
10kV
(250) R2
SCALE =
R1
R3 = 5R1
R1 > 20kV
mV/g
b. Using the UCA to Change the Scale Factor
and Zero g Bias
Figure 14. Application Circuit for Increasing Scale Factor
AOUT
The accelerometer output (Pin 8) is set to a nominal scale factor of 250 mV/g (for VDD = 5 V). Note that AOUT is guaranteed
to source/sink a minimum of 50 µA (approximately 50 kΩ output impedance). So a buffer may be required between AOUT and
some A-to-D converter inputs.
T OUT
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 Figures 15a through 15d.
–6–
REV. A
ADXL105
So given a bandwidth of 1000 Hz, the typical rms noise floor of
an ADLX105 will be:
Output Scaling
The acceleration output (AOUT) of the ADXL105 is nominally
250 mV/g. This scale factor may not be appropriate for all applications. The UCA may be used to increase the scale factor. The
simplest implementation would be as shown in Figure 14a.
Since the 0 g offset of the ADXL105 is 2.5 V ± 625 mV, using a
gain of greater than 4 could result in having the UCA output at
0 V or 5 V at 0 g. The solution is to add R3 and VR1, as shown
in Figure 14b, turning the UCA into a summing amplifier. VR1
is adjusted such that the UCA output is VDD/2 at 0 g.
Noise = (225 µg/√Hz) × (√1000 × 1.6)
= 9 mg rms for a single-pole filter
and
Noise = (225 µg/√Hz) × (√1000 × 1.4)
= 8.4 mg rms for 2-pole filter
Often the peak value of the noise is desired. Peak-to-peak noise
can only be estimated by statistical means. Table I may be used
for estimating the probabilities of exceeding various peak values
given the rms value. The peak-to-peak noise value will give the
best estimate of the uncertainty in a single measurement.
C
f–3dB =
R1
R2
IN
OUT
1
2pCR1
GAIN = – R1
R2
VMID
Table I. Estimation of Peak-to-Peak Noise
a. 1-Pole Low-Pass Filter
0.22mF
20kV
20kV
IN
OUT
0.18mF
f–3dB = 30Hz
VMID
b. 2-Pole Bessel Low-Pass Filter
R1
f–3dB =
C
R2
IN
R3
OUT
VMID
Nominal Peak-toPeak Value
% of Time that Noise Will
Exceed Peak-to-Peak Value
2 × rms
3 × rms
4 × rms
5 × rms
6 × rms
7 × rms
8 × rms
32%
13%
4.6%
1.2%
0.27%
0.047%
0.0063%
The UCA may be configured to act as an active filter with gain
and 0 g offset control as shown in Figure 16.
1
2pCR2
GAIN = – R1
R2
0.1mF
R3 ~
~ 2.5 R1
VDD
VMID
c. 1-Pole High-Pass Filter
10kV
47kV
44.2kV
100kV
OUT
IN
0.39mF
47kV
0.39mF
47kV
IN
59kV
VMID
GAIN = 2
f–3dB = 30Hz
OUT
Figure 16. UCA Configured as an Active Low-Pass Filter
with Gain and Offset
f–3dB = 10Hz
d. 2-Pole Bessel High-Pass Filter
EMC and Electrical Noise
The design of the ADXL105 is such that EMI or magnetic
fields do not normally affect it. Since the ADXL105 is ratiometric, conducted electrical noise on VDD does affect the output.
This is particularly true for noise at the ADXL105’s internal
clock frequency (200 kHz) and its odd harmonics. So maintaining a clean supply voltage is key in preserving the low noise and
high resolution properties of the ADXL105.
Figure 15. UCA Used as Active Filters*
Device Bandwidth vs. Resolution
In general the bandwidth selected will determine the noise floor
and hence, the measurement resolution (smallest detectable
acceleration) of the ADXL105. Since the noise of the ADXL105
has the characteristic of white Gaussian noise that contributes
equally at all frequencies, the noise amplitude may be reduced
by simply reducing the bandwidth. So the typical noise of the
ADXL105 is:
Noise (rms) = (225 µg/√Hz) × (√Bandwidth × K)
One way to ensure that VDD contains no high frequency noise is
to add an R-C low-pass filter near the VDD pin as shown in
Figure 17. Using the component values shown in Figure 17,
noise at 200 kHz is attenuated by approximately –23 dB. Assuming the ADXL105 consumes 2 mA, there will be a 100 mV
drop across R1. This can be neglected simply by using the
ADXL105’s VDD as the A-to-D converter’s reference voltage as
shown in Figure 17.
Where
K ≈ 1.6 for a single-pole filter
K ≈ 1.4 for a 2-pole filter
*For other corner frequencies, consult an active filter handbook.
REV. A
0.1mF
–7–
ADXL105
VDD
VDD
0.22mF
TEMP
SENSOR
TOUT
ADXL105
UNCOMMITTED
AMPLIFIER
VREF
The resonant frequency of the beam in the ADXL105 determines its high frequency limit. However the resonant frequency
of the Cerpak package is typically around 7 kHz. As a result, it
is not unusual to see 6 dB peaks occurring at the package resonant frequency (as shown in Figures 12 and 13). Indeed, the
PCB will often have one or more resonant peaks well below
7 kHz. Therefore, if the application calls for accurate operation
at or above 6 kHz the ADXL105 should be glued to the PCB in
order to eliminate the amplitude response peak due to the package, and careful consideration should be given to the PCB
mechanical design.
DOUT
ST
AIN
X SENSOR
COM
COM
AOUT
VMID VNIN VIN
UCAOUT
COM
A-TO-D
CONVERTER
Figure 17. Reducing Noise on VDD
Dynamic Operation
In applications where only dynamic accelerations (vibration) are
of interest, it is often best to ac-couple the accelerometer output
as shown in Figures 15c and 15d. The advantage of ac coupling
is that 0g offset variability (part to part) and drifts are eliminated.
C3549a–1–9/99
5 kHz where it gently rolls off (see Figure 7). The beam resonance at 16 kHz can be seen in Figure 7 where there is a small
noise peak (+5 dB) at the beam’s resonant frequency. There are
no other significant noise peaks at any frequency.
50V
+V
CALIBRATING THE ADXL105
The initial value of the offset and scale factor for the ADXL105
will require dc calibration for applications such as tilt
measurement.
Low Power Operation
The most straightforward method of lowering the ADXL105’s
power consumption is to minimize its supply voltage. By lowering VDD from 5 V to 2.7 V the power consumption goes from
9.5 mW to 3.5 mW. There may be reasons why lowering the
supply voltage is impractical in many applications, in which case
the best way to minimize power consumption is by power cycling.
For low g applications, the force of gravity is the most stable,
accurate and convenient acceleration reference available. An
approximate reading of the 0 g point can be determined by
orienting the device parallel to the Earth’s surface and then
reading the output. For high accuracy, a calibrated fixture must
be used to ensure exact 90 degree orientation to the 1 g gravity
signal.
The ADXL105 is capable of turning on and giving an accurate
reading within 700 µs (see Figure 18). Most microcontrollers
can perform an A-to-D conversion in under 25 µs. So it is practical to turn on the ADXL105 and take a reading in under 750
µs. Given a 100 Hz sample rate the average current required at
2.7 V would be:
100 samples/s × 750 µs × 1.3 mA = 97.5 µA
An accurate sensitivity calibration method is to make a measurement at +1 g and –1 g. The sensitivity can be determined by the
two measurements. This method has the advantage of being less
sensitive to the alignment of the accelerometer because the on
axis signal is proportional to the Cosine of the angle. For example, a 5° error in the orientation results in only a 0.4% error
in the measurement.
To calibrate, the accelerometer measurement axis is pointed
directly at the Earth. The 1 g reading is saved and the sensor is
turned 180° to measure –1 g. Using the two readings and sensitivity is calculated:
Sensitivity = [1 g Reading – (–1 g Reading)]/2 V/g
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
Figure 18. Typical Turn-On Response at VDD = 5 V
PRINTED IN U.S.A.
14-Lead Cerpak
(QC-14)
0.415 (10.541)
MAX
Note that if a filter is used in the UCA, sufficient time must be
allowed for the settling of the filter as well.
14
8
0.310 (7.874)
0.275 (6.985)
Broadband Operation
0.419 (10.643)
0.394 (10.008)
1
The ADXL105 has a number of characteristics that permits
operation over a wide frequency range. Its frequency and phase
response is essentially flat from dc to 10 kHz (see Figures 12
and 13). Its sensitivity is also constant over temperature (see
Figure 3). In contrast, most accelerometers do not have linear
response at low frequencies (in many cases, no response at very
low frequencies or dc), and often have a large sensitivity temperature coefficient that must be compensated for. In addition, the ADXL105’s noise floor is essentially flat from dc to
PIN 1
0.170 (4.318)
0.135 (3.429)
0.020 (0.508)
0.004 (0.102)
–8–
7
0.345 (8.763)
0.290 (7.366)
0.300 (7.62)
0.190 (4.826)
0.140 (3.556)
0.050 0.020 (0.508)
(1.27) 0.013 (0.330)
BSC
SEATING
0.0125 (0.318)
PLANE
0.009 (0.229)
88
08
0.050 (1.270)
0.016 (0.406)
REV. A
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