DAC8512

–13–

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

Ω/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.

0.1

µF

+5V

5

6

8

DAC8512

1

CS

3

4

7

2

0.1

µF

10k

Ω

+5V

VOUT

+5V

+5V

+5V

10k

Ω

SCLK

10k

Ω

SDI

10k

Ω

LD

LD

SCLK

SDI

+5V

REG

+5V

POWER

HIGH VOLTAGE

ISOLATION

Figure 34. An Opto-Isolated DAC Interface

+5V

+5V

10k

Ω

10k

Ω

SCLK

SDI

+5V

REG

+5V

POWER

HIGH VOLTAGE

ISOLATION

74HC161

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

CLR

CLK

A

B

C

D

ENP

GND

V

CC

RCO

Q

A

Q

B

Q

C

Q

D

ENT

LOAD

+5V

10k

Ω

NC

NC

NC

0.1

µF

+5V

+5V

10k

Ω

X

1

2

3

Y

4

5

6

1/4 74HCOO

1/4 74HCOO

V

DD

0.1

µF

3

5

8

DAC8512

1

+5V

4

LD

SCLK

SDI

7

6

CLR

GND

V

OUT

CS

2

+5V

10k

Ω

1

µF

Figure 35. A Two-Wire, Opto-lsolated DAC Interface