1
2
3
4
5
6
7
8
9
DB15
DB14
DB13
DB12
DB11
DB10
DB9
NC 48
NC 47
NC 46
NC 45
V
OUTA Sense 44
–2.5V to +2.5V
V
OUTA 43
VREFL AB Sense 42
VREFL AB 41
–2.5V
+2.5V
DB8
Data
Bus
DB7
V
REFH AB 40
VREFH AB Sense 39
OUTB Sense 38
VOUT
37
OUTC Sense 36
VOUT
35
10 DB6
11 DB5
12 DB4
13 DB3
14 DB2
15 DB1
16 DB0
17 RSTSEL
18 RST
19 LOADDACS
20 R/W
21 A1
V
–2.5V to +2.5V
–2.5V to +2.5V
B
DAC7644
V
C
V
REFH CD Sense 34
+2.5V
–2.5V
VREFH CD 33
+5V
Reset DACs
VREFL CD 32
V
REFL CD Sense 31
Load DAC Registers
READ/WRITE
VOUTD Sense 30
–2.5V to +2.5V
V
OUTD 29
VSS 28
–5V
+5V
Address
0.1µF
1.0µF
1.0µF
+
+
22 A0
AGND 27
VCC 26
VDD 25
0.1µF
Chips Select
23 CS
24 DGND
NC = No Connection
FIGURE 3. Basic Dual-Supply Operation of the DAC7644.
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.
ANALOG OUTPUTS
When VSS = –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 VSS
= 0V (single-supply operation), and with RLOAD also con-
nected to ground, the output can swing to ground. Care must
also be taken when measuring the zero-scale error when VSS
= 0V. Since the output voltage cannot swing below ground,
the output voltage may not change for the first few digital
input codes (0000H, 0001H, 0002H, etc.) if the output ampli-
fier has a negative offset. At the negative limit of –2mV, the
first specified output starts at code 0040H.
NC 48
NC 47
NC 46
RW1
NC 45
V
OUTA Sense 44
OUTA 43
VREFL AB Sense 42
REFL AB 41
REFH AB 40
RW2
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 (RW2) 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.
VOUT
+V
V
DAC7644
V
V
+2.5V
VREFH AB Sense 39
RW1
VOUTB Sense 38
V
OUTB 37
RW2
VOUT
FIGURE 4. Analog Output Closed-Loop Configuration
(1/2 DAC7644). RW represents wiring resis-
tances.
®
16
DAC7644
BB [ BURR-BROWN CORPORATION ]
