AD7537 Analog Devices, AD7537 Datasheet - Page 6

• Manufacturer Part Number: AD7537
• Description: LC2MOS (8+4) Loading Dual 12-Bit DAC
• Manufacturer: Analog Devices

AD7537
SEPARATE AGND PINS
The DACs in the AD7537 have separate AGND lines taken to
pins AGNDA and AGNDB on the package. This increases the
applications versatility of the part. Figure 6 is an example of
this. DAC A is connected in standard fashion as a program-
mable attenuator. AGNDA is at ground potential. DAC B is op-
erating with AGND B biased to +5 V by the AD584. This gives
an output range of +5 V to +10 V.
PROGRAMMABLE OSCILLATOR
Figure 7 shows a conventional state variable oscillator in which
Figure 6. AD7537 DACs Used in Different Modes
Figure 7. Programmable State Variable Oscillator
–6–
the AD7537 controls the programmable integrators. The fre-
quency of oscillation is given by:
where R
DACs. The same digital code is loaded into both DACs.
If C1 = C2 and R5 = R6, the expression reduces to
Since R
where m is the DAC ladder resistance mismatch ratio, typically
1.005.
With the values shown in Figure 7, the output frequency varies
from 0 Hz to 1.38 kHz. The amplitude of the output signal at
the A3 output is 10 V peak-to-peak and is constant over the
entire frequency span.
EQ1
EQ
and R
f
2
f
2
2
n
1
1
2
N
1
2
EQ2
R
1
f
LAD
D
C
C R
are the equivalent resistances of the
C
1
2
R6
R5
1
, (R
R
D
LAD m
LAD1
R
LAD
LAD1
C
C1 C2 R
1
(N / 2
1
= DAC ladder resistance).
R
R
LAD2
EQ1
R
n
)
LAD2
2
1
1
R
EQ1
EQ2
D
R
EQ2
2
N
n
REV. 0