AD652 Analog Devices, AD652 Datasheet - Page 16

• Manufacturer Part Number: AD652
• Description: Monolithic Synchronous Voltage-to-Frequency Converter
• Manufacturer: Analog Devices

AD652
BRIDGE TRANSDUCER INTERFACE
The circuit of Figure 33 illustrates a simple interface between
the AD652 and a bridge-type transducer. The AD652 is an
ideal choice because its buffered 5 volt reference can be used as
the bridge excitation thereby ratiometrically eliminating the gain
drift related errors. This reference will provide a minimum of
10 mA of external current, which is adequate for bridge resis-
tance of 600 Ω and above. If, for example, the bridge resistance
is 120 Ω or 350 Ω, an external pull-up resistor (R
and can be calculated using the formula:
An instrumentation amplifier is used to condition the bridge sig-
nal before presenting it to the SVFC. The AD625, with its high
CMRR, minimizes common-mode errors and also can be set to
arbitrary gains between 1 and 10,000 via three resistors, simpli-
fying the scaling for the AD652’s calibrated 10 volt input range.
Figure 30. Delta Modulator lnput Signal and Ramp-Wise
Approximation
Figure 31. Delta Modulator Input Signal, Ramp-Wise
Approximation and Output Frequency
Figure 32. Maximum Integrating Cap Value vs. Input
Signal Bandwidth
R
PU
(max ) =
R
BRIDGE
5 V
+V
S
– 5 V
– 10 mA
PU
) is required
–16–
tion holds:
where 10 kΩ ≤ R
output voltage of the bridge.
The bridge output may be unipolar, as is the case for most
pressure transducers, or it may be bipolar as in some strain mea-
surements. If the signal is unipolar, the reference input of the
AD625 (Pin 7) is simply grounded. If the bridge has a bipolar
output, however, the AD652 reference can be tied to Pin 7,
thereby, converting a ± 5 volt signal (after gain) into a 0 volt to
+10 volt input for the SVFC.
These resistors should be selected such that the following equa-
0.200 (5.08)
0.200 (5.08)
0.125 (3.18)
0.048 (1.21)
0.042 (1.07)
0.005 (0.13) MIN
0.020
(0.50)
MAX
R
0.023 (0.58)
0.014 (0.36)
0.048 (1.21)
0.042 (1.07)
Figure 33. Bridge Transducer Interface
16
1
4
8
0.395 (10.02)
0.356 (9.04)
0.350 (8.89)
0.385 (9.78)
(PINS DOWN)
9
Dimensions shown in inches and (mm).
3
TOP VIEW
IDENTIFIER
PIN 1
F
0.840 (21.34) MAX
10 V = V
PIN 1
≤ 20 kΩ, and V
OUTLINE DIMENSIONS
0.100
(2.54)
BSC
19
13
SQ
SQ
0.056 (1.42)
0.042 (1.07)
18
14
0.080 (2.03) MAX
0.070 (1.78)
0.030 (0.76)
BRIDGE
(P-20A)
0.050
(1.27)
BSC
Cerdip
(Q-16)
PLCC
9
8
0.310 (7.87)
0.220 (5.59)
0.180 (4.57)
0.165 (4.19)
BRIDGE
0.060 (1.52)
0.015 (0.38)
0.110 (2.79)
0.085 (2.16)


SEATING
PLANE
2 R
0.150
(3.81)
MIN
R
G
F
is the maximum
+ 1
0.021 (0.53)
0.013 (0.33) 0.330 (8.38)
0.032 (0.81)
0.026 (0.66)
0.025 (0.63)
0.015 (0.38)
0.040 (1.01)
0.025 (0.64)


15°
0°
0.320 (8.13)
0.290 (7.37)
0.290 (7.37)
0.015 (0.38)
0.008 (0.20)
REV. B