Datasheet
–8–
AD7249
t
2
t
5
t
4
t
3
t
10
t
6
t
7
t
8
t
9
DB15 DB14 DB13 DB12 DB11 DB0 DB15 DB14 DB13 DB12 DB10 DB0
DON'T
CARE
DON'T
CARE
DON'T
CARE
DAC
SELECT
=0
MSB DON'T
CARE
DON'T
CARE
DON'T
CARE
DAC
SELECT
=1
MSBLSB LSB
DAC A DAC B
t
1
SCLK
SYNC
SDIN
LDAC
CLR
Figure 8. Timing Diagram
TRANSFER FUNCTION
The internal scaling resistors provided on the AD7249 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 can be set up for different output ranges.
Unipolar (0 V to +10 V) Configuration
The first of the configurations provides an output voltage range
of 0 V to +10 V. This is achieved by connecting the output
offset resistor R
OFSA
, R
OFSB
(Pin 3, 16) to AGND. Natural Bi-
nary data format is selected by connecting BIN/COMP (Pin 7)
to DGND. In this configuration, the AD7249 can be operated
using either single or dual supplies. Note that the V
DD
supply is
AD7249*
V
DD
V
DD
2R
2R
2R
2R
A1
A2
12-BIT
DAC A
12-BIT
DAC B
REFOUT
REFIN
R
OFSA
V
OUTA
0V TO 10V
R
OFSB
V
OUTB
0V TO 10V
BIN/COMP
DGNDAGND
0V OR V
SS
V
SS
*ADDITIONAL PINS OMITTED FOR CLARITY.
Figure 9. Unipolar (0 V to +10 V) Configuration
restricted to +15 V ± 10% for this range in order to maintain
sufficient amplifier headroom. Dual supplies may be used to
improve settling time and give increased current sink capability
for the amplifier. Figure 9 shows the connection diagram for
unipolar operation of the AD7249. Table I shows the digital
code vs. analog output for this configuration.
Unipolar (0 V to +5 V) Configuration
The 0 V to +5 V output voltage range is achieved by tying
R
OFSA
to V
OUTA
or R
OFSB
to V
OUTB
. Once again, the AD7249
can be operated using either single or dual supplies. The table
for output voltage versus digital code is as in Table I, with
2REFIN replaced by REFIN. Note, for this range, 1 LSB =
REFIN × (2
–12
) = (REFIN/4096).
Table I. Unipolar Code Table (0 V to +10 V Range)
Input Data Word
MSB LSB Analog Output, V
OUT
XXXY 1111 1111 1111 +2REFIN × (4095/4096)
XXXY 1000 0000 0001 +2REFIN × (2049/4096)
XXXY 1000 0000 0000 +2REFIN × (2048/4096) = +REFIN
XXXY 0111 1111 1111 +2REFIN × (2047/4096)
XXXY 0000 0000 0001 +2REFIN × (1/4096)
XXXY 0000 0000 0000 0 V
X = Don’t Care.
Y = DAC Select Bit, 0 = DAC A, 1= DAC B.
Note: 1 LSB = 2REFIN/4096.
REV. D