8

®

DAC80/80P

CURRENT OUTPUT MODELS

The resistive scaling network and equivalent output circuit

of the current model differ from the voltage model and are

shown in Figures 7 and 8.

Internal scaling resistors (Figure 7) are provided to scale an

external op amp or to configure load resistors for a voltage

output. These connections are described in the following

sections.

If the internal resistors are not used for voltage scaling,

external R

L

(or R

resistors should have a TCR of

±25ppm/°C or less to minimize drift. This will typically add

±50ppm/°C plus the TCR of R

Driving An External Op Amp

The current output model DAC80 will drive the summing

junction of an op amp used as a current-to-voltage converter

to produce an output voltage. See Figure 9.

V

where I

OUT

is the DAC80 output current and R

F

is the

feedback resistor. Using the internal feedback resistors of

Output

Digital

Connect

Connect

Connect

Connect

Range

Input Codes

Pin 15 to Pin 17 to

Pin 19 to

Pin 16 to

±10

COB or CTC

19

20

15

24

±5

COB or CTC

18

20

NC

24

±2.5V

COB or CTC

18

20

20

24

0 to +10V

CSB

18

21

NC

24

0 to +5V

CSB

18

21

20

24

TABLE III. Output Voltage Range Connections for Voltage

Models.

6.3k

Reference Input

To Reference Control Circuit

NOTE: (1) Resistor Tolerances: ±2% max.

19

17

16

3k

2k

5k

20

15

18

FIGURE 7. Internal Scaling Resistors.

FIGURE 8. Current Output Model Equivalent Output Circuit.

To

Reference

Control

Circuit

24 Reference Out

17 Bipolar Offset

21 Common

15 I

OUT

16 Reference Input

R

O

6.6k

Ω

6.3k

Ω

I

6.3V

+

–

0 to

2mA

FIGURE 9. External Op-Amp—Using Internal Feedback

Resistors.

19

18

21

15

6.6k

Ω

5k

Ω

I

OUT

0 to

2mA

A

10V Range

20V Range

5k

Ω

V

OUT

NOTE: (1) For fast settling.

the current output model DAC80 provides output voltage

ranges the same as the voltage model DAC80. To obtain the

desired output voltage range when connecting an external op

amp, refer to Table IV.

Output

Digital

Connect

Connect

Connect

Connect

Range

Input Codes

A to

Pin 17 to

Pin 19 to

Pin 16 to

±10V

COB or CTC

19

15

A

24

±5V

COB or CTC

18

15

NC

24

±2.5V

COB or CTC

18

15

15

24

0 to +10V

CSB

18

21

NC

24

0 to +5V

CSB

18

21

15

24

TABLE IV. Voltage Range of Current Output.

Output Larger Than 20V Range

For output voltage ranges larger than

±10V, a high voltage

op amp may be employed with an external feedback resistor.

Use I

–2mA for unipolar voltage ranges. See Figure 10. Use

protection diodes when a high voltage op amp is used.

The feedback resistor, R

ficient as low as possible. Using an external feedback

resistor, overall drift of the circuit increases due to the lack

of temperature tracking between R

resistor network. This will typically add 50ppm/

°C plus R

F

drift to total drift.

FIGURE 10. External Op-Amp—Using External Feedback

Resistors.

24

17

21

15

16

6.6k

Ω

6.3k

Ω

I

0 to

2mA

+

–

6.3k

Ω

R

F

NOTE: (1) For output voltage swings up to 290V p-p.

V

OUT