DAC8512 Datasheet, PDF (13/20 Pages) Analog Devices – % V, Serial Input Complete 12-Bit DAC

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 kΩ/1 µF 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
LD
SCLK
SDI
DAC8512
HIGH VOLTAGE
ISOLATION
+5V
REG
+5V
+5V
10kΩ
LD
+5V
10kΩ
SCLK
+5V
10kΩ
SDI
+5V
10kΩ
0.1µF
6
+5V
0.1µF
1
5
DAC8512
3
8
4
VOUT
CS
2
7
POWER
SCLK
SDI
REV. A
Figure 34. An Opto-Isolated DAC Interface
HIGH VOLTAGE
ISOLATION
+5V
REG
+5V
10kΩ
+5V
10kΩ
+5V
10kΩ
+5V
+5V
10kΩ
+5V
1µF
74HC161
0.1µF
1 CLR
V_CC 16
2 CLK
RCO 15
NC
3A
Q_A 14
NC
4B
Q_B 13
NC
5C
Q_C 12
6D
Q_D 11
7 ENP
ENT 10
8 GND LOAD 9
1/4 74HCOO
1
3
2X
+5V
10kΩ
1/4 74HCOO
4
6
5Y
+5V _0.1µF
6
1
5 LD CLR V_DD
3 SCLK
8
DAC8512
4 SDI
2 CS
GND
7
V_OUT
Figure 35. A Two-Wire, Opto-lsolated DAC Interface
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