Datasheet
16
®
DAC7644
DB15
DB14
DB13
DB12
DB11
DB10
DB9
DB8
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
RSTSEL
RST
LOADDACS
R/W
A1
A0
CS
DGND
NC
NC
NC
NC
V
OUT
A Sense
V
OUT
A
V
REF
L AB Sense
V
REF
L AB
V
REF
H AB
V
REF
H AB Sense
V
OUT
B Sense
V
OUT
B
V
OUT
C Sense
V
OUT
C
V
REF
H CD Sense
V
REF
H CD
V
REF
L CD
V
REF
L CD Sense
V
OUT
D Sense
V
OUT
D
V
SS
AGND
V
CC
V
DD
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
DAC7644
Reset DACs
Data
Bus
Address
Load DAC Registers
READ/WRITE
Chips Select
NC = No Connection
–2.5V to +2.5V
–2.5V
–2.5V to +2.5V
–2.5V to +2.5V
–2.5V to +2.5V
+2.5V
+2.5V
–2.5V
+5V
+5V
–5V
0.1µF
0.1µF 1.0µF
1.0µF
+
+
FIGURE 3. Basic Dual-Supply Operation of the DAC7644.
ANALOG OUTPUTS
When V
SS
= –5V (dual supply operation), the output ampli-
fier can swing to within 2.25V of the supply rails, guaran-
teed over the –40°C to +85°C temperature range. With V
SS
= 0V (single-supply operation), and with R
LOAD
also con-
nected to ground, the output can swing to ground. Care must
also be taken when measuring the zero-scale error when V
SS
= 0V. Since the output voltage cannot swing below ground,
the output voltage may not change for the first few digital
input codes (0000
H
, 0001
H
, 0002
H
, etc.) if the output ampli-
fier has a negative offset. At the negative limit of –2mV, the
first specified output starts at code 0040
H
.
Due to the high accuracy of these D/A converters, system
design problems such as grounding and contact resistance
become very important. A 16-bit converter with a 2.5V full-
scale range has a 1LSB value of 38µV. With a load current
of 1mA, series wiring and connector resistance (see Figure
4) of only 40mΩ (R
W2
) will cause a voltage drop of 40µV.
To understand what this means in terms of a system layout,
the resistivity of a typical 1 ounce copper-clad printed circuit
board is 1/2 mΩ per square. For a 1mA load, a 10 milli-inch
wide printed circuit conductor 600 milli-inches long will
result in a voltage drop of 30µV.
The DAC7644 offers a force and sense output configuration
for the high open-loop gain output amplifier. This feature
allows the loop around the output amplifier to be closed at
the load (see Figure 4), thus ensuring an accurate output
voltage.
NC
NC
NC
NC
V
OUT
A Sense
V
OUT
A
V
REF
L AB Sense
V
REF
L AB
V
REF
H AB
V
REF
H AB Sense
V
OUT
B Sense
V
OUT
B
48
47
46
45
44
43
42
41
40
39
38
37
DAC7644
R
W1
R
W2
+2.5V
+V
V
OUT
R
W1
R
W2
V
OUT
FIGURE 4. Analog Output Closed-Loop Configuration
(1/2 DAC7644). R
W
represents wiring resis-
tances.