DAC8512GBC Analog Devices, DAC8512GBC Datasheet - Page 13

• Manufacturer Part Number: DAC8512GBC
• Description: % V/ Serial Input Complete 12-Bit DAC
• Manufacturer: Analog Devices

REV. A
Opto-Isolated Interfaces for Process Control Environments
In many process control type applications, it is necessary to pro-
vide an isolation barrier between the controller and the unit be-
ing controlled. Opto-isolators can provide isolation in excess of
3 kV. The serial loading structure of the DAC8512 makes it
ideal for opto-isolated interfaces as the number of interface lines
is kept to a minimum.
Illustrated in Figure 34 is an opto-isolated interface using the
DAC8512. In this circuit, the CS line is always LOW to enable
the DAC, and the 10 k /1 F combination connected to the
DAC’s CLR pin sets a turn-on time constant of 10 ms to reset
the DAC upon application of power. Three opto-couplers are
then used for the SDI, SCLK, and LD lines.
Often times reducing the number of interface lines to two lines
is required in many control environments. The circuit illustrated
in Figure 35 shows how to convert a two-line interface into the
three control lines required to control the DAC8512 without us-
ing one shots. This technique uses a counter to keep track of the
clock cycles and, when all the data has been input to the DAC,
the external logic generates the LD pulse.
POWER
SCLK
SDI
+5V
+5V
HIGH VOLTAGE
ISOLATION
10k
10k
+5V
10k
+5V
REG
Figure 35. A Two-Wire, Opto-lsolated DAC Interface
+5V
1
2
3
4
5
6
7
8
CLR
CLK
A
B
C
D
ENP
GND
74HC161
LOAD
RCO
ENT
V
Q
Q
Q
Q
CC
A
B
C
D
16
15
14
13
12
10
11
9
+5V
–13–
NC
NC
NC
0.1 F
POWER
SCLK
+5V
1
2
10k
SDI
LD
1/4 74HCOO
+5V
X
10k
Figure 34. An Opto-Isolated DAC Interface
1 F
3
4
5
1/4 74HCOO
Y
HIGH VOLTAGE
ISOLATION
+5V
+5V
+5V
6
10k
SCLK
10k
SDI
10k
LD
5
3
4
2
+5V
REG
SCLK
CS
LD
SDI
0.1 F
10k
CS
CLR
DAC8512
+5V
6
GND
7
+5V
V
6
5
3
4
2
+5V
DD
1
DAC8512
DAC8512
0.1 F
8
+5V
1
7
V
OUT
0.1 F
8
V OUT