AD698AP datasheet(11/12 Pages) AD

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AD698

REV. B

–11–

VOUT =

× R

RG + 1









×V

Solving for VOUT/VIN = 400 and setting RG = 100

Ω then:

RS = [400 – 1]

× R

G/2 = 19.95 k

Ω

Choose an oscillator amplitude that is in the range of 1 V to

3.5 V rms. For an input excitation level of 3 V rms, the output

signal from the amplifier gain stage will be 3.5 V rms

× 0.8 V or

2.4 V rms, which is in the acceptable range.

Since A/B is known, the value of R2, the output FS resistor may

be chosen by the formula:

VOUT = A/B × 500 µA × R2

For a 10 V output at FS, with an A/B of 0.8; solve for R2.

R2 = 10 V [0.8

× 500 µA] = 25.0 kΩ

This will result in a VOUT of 10 V for a full-scale signal from the

bridge. The other components, C1, C2, C3, C4 may be selected

by following the guidelines on general device operation men-

tioned earlier.

If a gain trim is required, then a trim resistor can be used to ad-

just either R2 or RG. Bridge offsets should be adjusted by a trim

network on the OFFSET 1 and OFFSET 2 pins of the AD698.

1000pF

SIGNAL

REFERENCE

VOUT

100nF

6.8µF

–15V

+15V

100nF

6.8µF

PHASE

LAG/LEAD

NETWORK

AD698

–VS

EXC1

EXC2

LEV1

LEV2

FREQ1

BFILT1

BFILT2

–BIN

+BIN

–AIN

FREQ2

SIG REF

OFFSET2

OFFSET1

+VS

OUT FILT

FEEDBACK

SIG OUT

–ACOMP

AFILT2

AFILT1

+ACOMP

+AIN

RESISTORS,

INDUCTORS

OR CAPACITORS

PHASE LEAD

PHASE LAG

PHASE LAG = Arc Tan (Hz RC);

PHASE LEAD = Arc Tan 1/(Hz RC)

WHERE R = RS// (RS + RT)

DUAL

OP AMP

Figure 20. AD698 Interconnection Diagram for AC Bridge Applications

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