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acquire and process the spectral content of a sensor s signal
RF
rather than its dc level, the wideband characteristics of the
CF
2 4 6
IN AD215 prove most useful. Key specifications for ac transducer
IN COM
RG
applications include bandwidth, slew rate and harmonic distor-
1 3 5
+VISO
VISO
tion. Since the transducer may be mechanically bonded or
RF C2 C1 welded to the object under test, isolation is typically required to
CF
2 4 6
eliminate ground loops as well as protect the electronics used in
IN
IN COM
RG the data acquisition system. Figure 23 shows an isolated strain
1 3 5
+VISO
gage circuit employing the AD215 and a high speed operational
VISO
amplifier (AD744).
C1, C2 ARE VISO FILTER CAPACITORS.
C2
C1
RF, RG ARE FEEDBACK, GAIN RESISTORS.
To alleviate the need for an instrumentation amplifier, the
CF IS A FEEDBACK BYPASS CAPACITOR.
bridge is powered by a bipolar excitation source. Under this ap-
proach the common-mode voltage is ±VSPAN which is typically
Figure 20b. PCB Layout for Gain Greater than Unity
only a few millivolts, rather than the VEXC 2 that would be
achieved with a unipolar excitation source and Wheatstone
APPLICATIONS EXAMPLES
bridge configuration.
Motor Control
Using two strain gages with a gage factor of 3 mV/V and a
Figure 21 shows an AD215 used in a dc motor control applica-
±1.2 V excitation signal, a ±6.6 mV output signal will result. A
tion. Its excellent phase characteristics and wide bandwidth are
gain setting of 454 will scale this low level signal to ±3 V, which
ideal for this type of application.
can then be digitized by a high speed, 100 kHz sampling ADC
ENCODER FEEDBACK
such as the AD7870.
AD215
ISOLATED
G = 1
4
MOTOR
The low voltage excitation is used to permit the front-end cir-
IMOTOR
COMMAND
MOTOR
OPTICAL
3
SHAFT
COMMAND cuitry to be powered from the isolated power supplies of the
38 RESOLVER
MOTOR
1 ±10V VC CONTROL MOTOR OR
TACHOMETER AD215, which can supply up to ±10 mA of isolated power at
±10 VOLTS UNIT
37 ¸
OUT LO ENCODER
2
±15 V. The bridge draws only 3.5 mA, leaving sufficient cur-
COM
rent to power the micropower dual BiFET (400 µA quiescent
current) and the high speed AD744 BiFET amplifier (4 mA
Figure 21. Motor Control Application
quiescent current).
Multichannel Data Acquisition
The current drive capabilities of the AD215 s bipolar ±15 V dc
isolated power supply is more than adequate to meet the modest
±800 µA supply current requirements for the AD7502 multi-
plexer. Digital isolation techniques should be employed to iso-
late the Enable (EN), A0 and A1 logic control signals.
EN A1 A0
AD7502
( 15V)
DTL/TTL TO CMOS LEVEL
TRANSLATOR
GND
DECODER/DRIVER
(+15V)
AD215
FB
G = 1
4
IN
3
OUT HI
38
S1 S4 S5 S8
IN+
1
IN COM OUT LO
2 37
+VISO
6 42 +15V
6.8µF
COM
2 44 15V
6.8µF VISO
PWR
5 43
RTN
Figure 22. Multichannel Data Acquisition Application
10
REV. 0
AD215
+VISO +VISO
220&!
Q1
VISO
2N3904
1/2
AD648
1M&!
+1.2V
FB
4
350&!
38 OUT HI
2M&! IN OUTPUT
+µ
3
FILTER
AD744
MOD
IN+ DEMOD
AND
+VISO 350&!
1
BUFFER
µ OUT LO
37
10k&!
2.2pF
6.8k&! 1.2V
36 TRIM
500&! 9.76k&!
AD215
220&!
Q2
2N3906
453k&! +VISO
1/2
6
+15V
AD589 AD648 42
1k&!
VISO VISO
C1 6.8µF ISOLATED 430kHz
COM
2 DC 44 15V
POWER
SUPPLY
C2 6.8µF VISO OSC
43 PWR
5
RTN
Figure 23. Strain Gage Signal Conditioning Application
11
REV. 0
AD215
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
AD215 SIP PACKAGE
0.325 (8.3)
2.480 (63.0) MAX MAX
0.840
0.815
(21.4)
(20.7)
MAX
0.020 (0.5)
0.12 (3.0) TYP
°
30 TYP
0.015 (0.4)
0.094 (2.4)
0.165 (4.2)
0.16 (4.1) 0.16 (4.1) 0.010
0.135 (3.4)
(0.25)
2.15 (54.6)
0.2
(5.1)
0.250
(6.4)
0.1 (2.5) 0.1 (2.5)
0.05 (1.3) 1.50 (38.1)
0.11 (2.8)
37 43
0.325
1 5
BOTTOM VIEW OF 0.1
(8.3) 3
(2.5)
2 6 FOOTPRINT
MAX
4 36 38 42 44
0.11 (2.8)
0.712 (18.2) 0.712 (18.2)
0.022 (0.56) C
L
NOTE: PINS MEASURE 0.022 (0.56) x 0.010 (0.25) PRIOR TO TINNING.
TINNING MAY ADD UP TO 3 mils (0.003") TO THESE DIMENSIONS.
12
REV. 0
C2134 20 4/96
PRINTED IN U.S.A.
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