REV. B

–12–

AD817

HIGH SPEED DAC BUFFER

The wide bandwidth and fast settling time of the AD817 make

it a very good output buffer for high speed current output D/A

converters like the AD668. As shown in Figure 38, the op amp

establishes a summing node at ground for the DAC output. The

output voltage is determined by the amplifier’s feedback resistor

(10.24 V for a 1 k

Ω resistor). Note that since the DAC gener-

ates a positive current to ground, the voltage at the amplifier

output will be negative. A 100

Ω series resistor between the

noninverting amplifier input and ground minimizes the offset

effects of op amp input bias currents.

1

2

3

7

24

23

22

18

8

9

10

17

16

15

11

12

14

13

4

5

21

20

6

19

AD668

+15V

10

µF

TO ANALOG

GROUND PLANE

0.1

µF

1V NOMINAL

REFERENCE INPUT

10k

Ω

1k

Ω

100

Ω

AD817

ANALOG GROUND PLANE

ANALOG

OUTPUT

ANALOG

SUPPLY

GROUND

0.1

µF

10

µF

–15V

+5V

1k

Ω

100pF

DIGITAL

INPUTS

MSB

LSB

V

REFCOM

REFIN1

REFIN2

R

ACOM

LCOM

IBPO

V

THCOM

VTH

EE

LOAD

OUT

CC

I

Figure 38. High Speed DAC Buffer

OUTLINE DIMENSIONS

Dimensions shown in inches and (mm).

8-Pin Plastic Mini-DIP

(N-8)

0.011

±0.003

(0.28

±0.08)

0.30 (7.62)

REF

15

°

0

°

PIN 1

4

5

8

1

0.25

(6.35)

0.31

(7.87)

0.10

(2.54)

BSC

SEATING

PLANE

0.035

±0.01

(0.89

±0.25)

0.18

±0.03

(4.57

±0.76)

0.033

(0.84)

NOM

0.018

±0.003

(0.46

±0.08)

0.125

(3.18)

MIN

0.165

±0.01

(4.19

±0.25)

0.39 (9.91) MAX

8-Pin SOIC

(SO-8)

0.0098 (0.25)

0.0075 (0.19)

0.0500 (1.27)

0.0160 (0.41)

8

°

0

°

0.0196 (0.50)

0.0099 (0.25)

x 45

°

PIN 1

0.1574 (4.00)

0.1497 (3.80)

0.2440 (6.20)

0.2284 (5.80)

4

5

1

8

0.0192 (0.49)

0.0138 (0.35)

0.0500

(1.27)

BSC

0.0688 (1.75)

0.0532 (1.35)

0.0098 (0.25)

0.0040 (0.10)

0.1968 (5.00)

0.1890 (4.80)