ADXL150AQC Analog Devices Inc, ADXL150AQC Datasheet - Page 9

• Manufacturer Part Number: ADXL150AQC
• Description: IC ACCELEROMETER LP SGL 14CERPAK
• Manufacturer: Analog Devices Inc
• Series: iMEMS®r

Specifications of ADXL150AQC

• Rohs Status: RoHS non-compliant
• Axis: X or Y
• Acceleration Range: ±50g
• Sensitivity: 38mV/g
• Voltage - Supply: 4 V ~ 6 V
• Output Type: Analog
• Bandwidth: 1kHz
• Mounting Type: Surface Mount
• Package / Case: 14-CerPak
• Interface: -

REV. 0
Adjusting the Zero g Bias Level
When a true dc (gravity) response is needed, the output from
the accelerometer must be dc coupled to the external amplifier’s
input. For high gain applications, a zero g offset trim will also be
needed. The external offset trim permits the user to set the zero g
offset voltage to exactly +2.5 volts (allowing the maximum output
swing from the external amplifier without clipping with a +5
supply).
With a dc coupled connection, any difference between the zero g
output and +2.5 V will be amplified along with the signal. To
obtain the exact zero g output desired or to allow the maximum
output voltage swing from the external amplifier, the zero g offset
will need to be externally trimmed using the circuit of Figure 20.
The external amplifier’s maximum output swing should be
limited to 2 volts, which provides a safety margin of 0.25
volts before clipping. With a +2.5 volt zero g level, the maxi-
mum gain will equal:
38 mV/g Times the Max Applied Acceleration in g
NOTES:
0 g “QUICK” CALIBRATION METHOD USING RESISTOR R2 AND A +5V SUPPLY.
(d) FOR V
(e) FOR V
(a) WITH ACCELEROMETER ORIENTED AWAY FROM EARTH’S
(b) CALCULATE THE OFFSET VOLTAGE THAT NEEDS TO BE NULLED:
( c) R2 = ––––––––
+V
GRAVITY (i.e., SIDEWAYS), MEASURE PIN 10 OF THE ADXL150.
V
S
0.1 F
OS
C1
=(+2.5V – V
2.5V (R3)
PIN
PIN
Figure 18. Offset Nulling the ADXL150/ADXL250 Using a Trim Potentiometer
V
OS
10 > +2.5V, R2 CONNECTS TO GND.
10 < +2.5V, R2 CONNECTS TO +V
2 Volts
14
SENSOR
PIN
SELF-TEST
+V
(DO NOT CONNECT)
0.1 F
10)(R3/R1).
S
ADXL150
C1
9
Figure 17. “Quick Zero g Calibration” Connection
TP
5
CLOCK
14
COM
SENSOR
SELF-TEST
GAIN
AMP
(DO NOT CONNECT)
ADXL150
9
7
DEMODULATOR
S
TP
.
5
R
30k
IN
OFFSET
CLOCK
AT PIN 8
0.1 F
GAIN
NULL
AMP
10k
C2
COM
25k
+V
2
S
DEMODULATOR
–9–
7
8
5k
+V
+V
The device scale factor and zero g offset levels can be calibrated
using the earth’s gravity, as explained in the section “calibrating
the ADXL150/ADXL250.”
Using the Zero g “Quick-Cal” Method
In Figure 18 (accelerometer alone, no external op amp), a trim
potentiometer connects directly to the accelerometer’s zero g
null pin. The “quick offset calibration” scheme shown in Figure
17 is preferred over using a potentiometer, which could change
its setting over time due to vibration. The “quick offset calibra-
tion” method requires measuring only the output voltage of
the ADXL150/ADXL250 while it is oriented normal to the
earth’s gravity. Then, by using the simple equations shown in
the figures, the correct resistance value for R2 can be calculated.
In Figure 17, an external op amp is used to amplify the signal. A
resistor, R2, is connected to the op amp’s summing junction.
The other side of R2 connects to either ground or +V
ing on which direction the offset needs to be shifted.
2
S
S
0.1 F
BUFFER
OR GND
AMP
C2
25k
+V
2
S
200k
10
SCALE FACTOR
8
76mV/ g
100mV/ g
200mV/ g
400mV/ g
5k
DESIRED
OFFSET
NULL
OUTPUT
R2 (SEE NOTES)
R1
BUFFER
AMP
+V
S
3
10
2
RANGE
OP196
FS
25 g
20 g
10 g
5 g
+V
V
4
7
OUT
S
100k
R3
GAIN
AMP
EXT
0.1 F
2.0
2.6
5.3
10.5
C4
ADXL150/ADXL250
6
VALUE
49.9k
38.3k
18.7k
9.53k
R1
V
OUT
S
depend-