DAC7631_09 Datasheet, PDF (12/22 Pages) Texas Instruments – Serial Input, 16-Bit, Voltage Output DIGITAL-TO-ANALOG CONVERTER

+2.5000V
Serial Data Out
Serial Data In
Clock
Chip Select
1 V_REFH
V_CC 20
2 V_REFH Sense
AGND 19
3 V_REFL
V_SS 18
4 V_REFL Sense
V_OUT Sense 17
5 DGND
6 V_DD
DAC7631
V_OUT 16
NC 15
7 SDO
RSTSEL 14
8 SDI
RST 13
9 CLK
LOAD 12
10 CS
LDAC 11
FIGURE 2. Basic Single-Supply Operation.
+5V
+
0.1µF 1µF
0V to +2.5V
Reset DAC Registers
Load
Load DAC Registers
+5V
+2.5000V
+
–2.5000V
0.1µF 1µF
Serial Data Out
Serial Data In
Clock
Chip Select
1 V_REFH
V_CC 20
2 V_REFH Sense
AGND 19
3 V_REFL
V_SS 18
4 V_REFL Sense
V_OUT Sense 17
5 DGND
6 V_DD
DAC7631
V_OUT 16
NC 15
7 SDO
RSTSEL 14
8 SDI
RST 13
9 CLK
LOAD 12
10 CS
LDAC 11
+5V
0.1µF
0.1µF
+ _1µF
+
1µF
–5V
–2.5V to +2.5V
Reset DAC Registers
Load
Load DAC Registers
FIGURE 3. Basic Dual-Supply Operation.
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. When
V_SS = 0V (single-supply operation), and with R_LOAD also
connected 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 amplifier 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 of only
40mΩ (R_W2) will cause a voltage drop of 40µV, as shown in
Figure 4. 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 DAC7631 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 (as shown in Figure 4), thus ensuring an accurate
output voltage.
REFERENCE INPUTS
The reference inputs, V_REFL and V_REFH, can be any voltage
between V_SS + 2.5V and V_CC – 2.5V, provided that V_REFH
is at least 1.25V greater than V_REFL. The minimum output of
each DAC is equal to V_REFL plus a small offset voltage
(essentially, the offset of the output op amp). The maximum
output is equal to V_REFH plus a similar offset voltage. Note
that V_SS (the negative power supply) must either be
connected to ground or must be in the range of –4.75V to
–5.25V. The voltage on V_SS sets several bias points within
the converter. If V_SS is not in one of these two configura-
tions, the bias values may be in error and proper operation
of the device is not guaranteed.
®
DAC7631
12