ADXL105AQC Analog Devices Inc, ADXL105AQC Datasheet - Page 6

• Manufacturer Part Number: ADXL105AQC
• Description: IC ACCELEROMETER SGL 14CERPAK
• Manufacturer: Analog Devices Inc
• Series: iMEMS®r

Specifications of ADXL105AQC

• Rohs Status: RoHS non-compliant
• Axis: X, Z
• Acceleration Range: ±7g
• Sensitivity: 250mV/g
• Voltage - Supply: 2.7 V ~ 5.25 V
• Output Type: Analog
• Bandwidth: 12kHz
• Mounting Type: Surface Mount
• Package / Case: 14-CerPak
• Interface: -

ADXL105
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.
V
The ADXL105 has two power supply (V
The two pins should be connected directly together. The output
of the ADXL105 is ratiometric to the power supply. Therefore a
0.22 F decoupling capacitor between V
quired to reduce power supply noise. To further reduce noise,
insert a resistor (and/or a ferrite bead) in series with the V
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 V
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.
A
The accelerometer output (Pin 8) is set to a nominal scale fac-
tor of 250 mV/g (for V
to source/sink a minimum of 50 A (approximately 50 k out-
put impedance). So a buffer may be required between A
some A-to-D converter inputs.
DD
OUT
DD
, an electrostatic force is exerted on the beam of the
DD
= 5 V). Note that A
DD
DD
) pins, 13 and 14.
and COM is re-
OUT
is guaranteed
OUT
DD
and
–6–
V
V
reference output for the on board uncommitted amplifier (UCA)
as shown in Figures 14a and 14b. Its output impedance is ap-
proximately 10 k .
T
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.
Figure 14. Application Circuit for Increasing Scale Factor
+V
MID
MID
OUT
+V
SCALE =
GAIN
1
2
3
4
is nominally V
b. Using the UCA to Change the Scale Factor
and Zero g Bias
a. Using the UCA to Change the Scale Factor
0.22 F
T
0.22 F
T
OUT
ST
OUT
SCALE – mV/ g
ST
(250) R2
COM
R1
COM
1000
250
500
750
mV/ g
X SENSOR
X SENSOR
SENSOR
COM
SENSOR
COM
DD
TEMP
V
TEMP
V
DD
DD
50k
50k
50k
50k
/2. It is primarily intended for use as a
R1
V
A
V
A
DD
OUT
DD
OUT
100k
150k
200k
50k
R2
10k
V
V
MID
MID
+V
ADXL105
ADXL105
R1
R1
R3
V
V
NIN
NIN
UNCOMMITTED
UNCOMMITTED
AMPLIFIER
AMPLIFIER
V
V
IN
IN
R3 = 5R1
R1 > 20k
R2
R2
UCA
UCA
OUTPUT
REV. A
OUTPUT
OUT
OUT