AD7237A/AD7247A
APPLYING THE AD7237A/AD7247A
Unipolar (0 V to +5 V) Configuration
The internal scaling resistors provided on the AD7237A/
AD7247A allow several output voltage ranges. The part can
produce unipolar output ranges of 0 V to +5 V or 0 V to +10 V
and a bipolar output range of
±
5 V. Connections for the various
ranges are outlined below. Since each DAC has its own R
OFS
input the two DACs on each part can be set up for different
output ranges.
Unipolar (0 V to +10 V) Configuration
The 0 V to +5 V output voltage range is achieved by tying R
OFSA
or R
OFSB
to V
OUTA
or V
OUTB
. Once again, the AD7237A/
AD7247A can be operated single supply or from dual supplies.
The table for output voltage versus digital code is as in Table
III, with 2 • REF IN replaced by REF IN. Note, for this range,
1 LSB = REF IN • (2
–12
) = (REF IN/4096).
Bipolar Configuration
The first of the configurations provides an output voltage range
of 0 V to +10 V. This is achieved by connecting the output off-
set resistor, R
OFSA
, or R
OFSB
, to AGND (GND for AD7247A).
In this configuration, the AD7237A/AD7247A can be operated
from single or dual supplies. Figure 8 shows the connection dia-
gram for unipolar operation for DAC A of the AD7237A, while
the table for output voltage versus digital code in the DAC latch
is shown in Table III. Similar connections apply to the AD7247A.
The bipolar configuration for the AD7237A/AD7247A, which
gives an output range of –5 V to +5 V, is achieved by connect-
ing R
OFSA
, or R
OFSB
, to REF IN. The AD7237A/AD7247A must
be operated from dual supplies to achieve this output voltage
range. Figure 9 shows the connection diagram for bipolar opera-
tion for DAC A of the AD7247A. An AD586 provides the refer-
ence voltage for the DAC but this could be provided by the
on-chip reference by connecting REF OUT to REF IN. The
code table for bipolar operation is shown in Table IV. Similar
connections apply for the AD7237A.
Figure 8. Unipolar (0 to +10 V) Configuration
Table III. Unipolar Code Table (0 to +10 V Range)
Figure 9. Bipolar Configuration
Table IV. Bipolar Code Table
DAC Latch Contents
MSB
LSB
Analog Output, V
OUT
1111 1111 1111
1000 0000 0001
1000 0000 0000
0111 1111 1111
0000 0000 0001
0000 0000 0000
Note: 1 LSB = REF IN/2048.
+2 • REF IN (4095/4096)
+2 • REF IN (2049/4096)
+2 • REF IN (2048/4096) = +REF IN
+2 • REF IN (2047/4096)
+2 • REF IN (1/4096)
0V
DAC Latch Contents
MSB
LSB
1111 1111 1111
1000 0000 0001
1000 0000 0000
0111 1111 1111
0000 0000 0001
0000 0000 0000
Note: 1 LSB = REF IN/2048.
Analog Output, V
OUT
+REF IN • (2047/2048)
+REF IN • (1/2048)
0V
–REF IN • (1/2048)
–REF IN • (2047/2048)
–REF IN • (2048/2048) = –REF IN
–10–
REV. 0
AD [ ANALOG DEVICES ]
