AD7937AR Analog Devices Inc, AD7937AR Datasheet - Page 6

• Manufacturer Part Number: AD7937AR
• Description: IC,D/A CONVERTER,DUAL,12-BIT,CMOS,SOP,24PIN
• Manufacturer: Analog Devices Inc

Specifications of AD7937AR

• Rohs Status: RoHS non-compliant
• Settling Time: 1µs
• Number Of Bits: 12
• Data Interface: Parallel
• Number Of Converters: 2
• Voltage Supply Source: Single Supply
• Power Dissipation (max): 24mW
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-SOIC (7.5mm Width)

AD7937
SEPARATE AGND PINS
The DACs in the AD7937 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 programmable
attenuator. AGNDA is at ground potential. DAC B is operating
with AGND B biased to 5 V by the AD584. This gives an out-
put range of 5 V to 10 V.
20V p–p
INPUT
DATA
GROUND
SIGNAL
DGND
V
V
DB7
DB0
REFA
V
REFB
CONTROL CIRCUITRY OMITTED FOR CLARITY
DD
= 5V
AD7937
DAC B
DAC A
NOTE
DAC CONTROL INPUTS OMITTED FOR CLARITY
SELECT CODE
10k
FREQUENCY
A1
R6
AD711
AGNDA
AGNDB
I
R
I
OUTA
R
OUTB
FBA
FBB
AD584
DAC A
1/2 AD7937
V
REFA
5V
A1
A2
AGNDA
I
OUTA
200k
V
R4
V
V
TO 10V
DD
OUTA
OUTB
= 5V
10,000pF
10k
A2
AD712
C1
R5
1/2
10k
PROGRAMMABLE OSCILLATOR
Figure 7 shows a conventional state variable oscillator in which
the AD7937 controls the programmable integrators. The frequency
of oscillation is given by:
where R
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.
5.1V
DAC B
V
1/2 AD7937
REFB
EQ1
EQ
AGNDB
=
and R
=
=
I
f =
OUTB
2
f =
2π
2 π
n
1
1
× R
2 π
EQ2
N
1
2 π
×
×
1
f =
LAD
D
C
C × R
×
are the equivalent resistances of the DACs.
C
1
10,000pF
2 π
R6
R5
1
, (R
R
AD712
A3
C2
D
LAD m
1/2
LAD1
R
×
×
LAD
LAD1
C
C1× C2 × R
1
(N / 2
1
× R
= DAC ladder resistance).
R
× R
LAD2
EQ1
n
V
)
LAD2
OUT
2
× R
1
1
EQ1
EQ2
D =
× R
EQ2



2
N
n


