DAC712 CALIBRATION VALUES
1 LEAST SIGNIFICANT BIT = 305
µ
V
DIGITAL INPUT CODE
BINARY TWO’S
COMPLEMENT, BTC
7FFF
H
|
4000
H
|
0001
H
0000
H
FFFF
H
|
C000
H
|
8000
H
ANALOG
OUTPUT
(V)
+9.999695
+5.000000
+0.000305
0.000000
–0.000305
–5.000000
–10.00000
1
2
DCOM
ACOM
V
OUT
28
27
26
25
DESCRIPTION
+ Full Scale –1LSB
3
4
3/4 Scale
BPZ + 1LSB
+12V to +15V
Bipolar Zero (BPZ)
–12V to –15V
BPZ – 1LSB
0.01µF
1/4 Scale
Minus Full Scale
0.01µF
+
+
5
6
7
8
9
10
11
12
13
V
REF OUT
24
23
+V
CC
–V
CC
22
21
20
19
18
17
16
15
TABLE I. Digital Input and Analog Output Voltage Calibra-
tion Values.
Gain Adjustment
Apply the digital input that gives the maximum positive
voltage output. Adjust the gain potentiometer or the gain
adjust D/A converter for this positive full scale voltage.
14
FIGURE 4. Power Supply Connections.
critical settling time may be able to use 0.01µF at –V
CC
as
well as at +V
CC
. The capacitors should be located close to
the package.
DAC712 has separate ANALOG COMMON and DIGITAL
COMMON pins. The current through DCOM is mostly
switching transients and are up to 1mA peak in amplitude.
The current through ACOM is typically 5µA for all codes.
Use separate analog and digital ground planes with a single
interconnection point to minimize ground loops. The analog
pins are located adjacent to each other to help isolate analog
from digital signals. Analog signals should be routed as far
as possible from digital signals and should cross them at
right angles. A solid analog ground plane around the D/A
package, as well as under it in the vicinity of the analog and
power supply pins, will isolate the D/A from switching
currents. It is recommended that DCOM and ACOM be
connected directly to the ground planes under the package.
If several DAC712s are used or if DAC712 shares supplies
with other components, connecting the ACOM and DCOM
lines to together once at the power supplies rather than at
each chip may give better results.
LOAD CONNECTIONS
Since the reference point for V
OUT
and V
REF OUT
is the
ACOM pin, it is important to connect the D/A converter load
directly to the ACOM pin. Refer to Figure 5.
Lead and contact resistances are represented by R
1
through
R
3
. As long as the load resistance R
L
is constant, R
1
simply
introduces a gain error and can be removed by gain adjust-
ment of the D/A or system-wide gain calibration. R
2
is part
of R
L
if the output voltage is sensed at ACOM.
In some applications it is impractical to return the load to the
ACOM pin of the D/A converter. Sensing the output voltage
at the SYSTEM GROUND point is reasonable, because
®
INSTALLATION
GENERAL CONSIDERATIONS
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 20V full-
scale range has a 1LSB value of 305µV. With a load current
of 5mA, series wiring and connector resistance of only
60mΩ will cause a voltage drop of 300µV. 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 5mA load, a 10 milli-inch wide printed
circuit conductor 60 milli-inches long will result in a voltage
drop of 150µV.
The analog output of DAC712 has an LSB size of 305µV
(–96dB). The noise floor of the D/A must remain below this
level in the frequency range of interest. The DAC712’s noise
spectral density (which includes the noise contributed by the
internal reference,) is shown in the Typical Performance
Curves section.
Wiring to high-resolution D/A converters should be routed
to provide optimum isolation from sources of RFI and EMI.
The key to elimination of RF radiation or pickup is small
loop area. Signal leads and their return conductors should be
kept close together such that they present a small capture
cross-section for any external field. Wire-wrap construction
is not recommended.
POWER SUPPLY AND
REFERENCE CONNECTIONS
Power supply decoupling capacitors should be added as
shown in Figure 4. Best performance occurs using a 1 to
10µF tantalum capacitor at –V
CC
. Applications with less
9
DAC712
ETC [ ETC ]
