AD847

REV. F

–12–

HIGH SPEED DAC BUFFER

The wide bandwidth and fast settling time of the AD847 makes

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

converters like the AD668. As shown in Figure 27, 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

1k

100

Ω

AD847

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 27. High Speed DAC Buffer

OUTLINE DIMENSIONS

Dimensions shown in inches and (mm).

All brand or product names mentioned are trademarks or registered trademarks of their respective holders.

Cerdip (Q-8) Package

0.320 (8.13)

0.290 (7.37)

0.015 (0.38)

0.008 (0.20)

15

°

0

°

0.005 (0.13) MIN

0.055 (1.40) MAX

1

PIN 1

4

5

8

0.310 (7.87)

0.220 (5.59)

0.405 (10.29) MAX

0.200

(5.08)

MAX

SEATING

PLANE

0.023 (0.58)

0.014 (0.36)

0.070 (1.78)

0.030 (0.76)

0.060 (1.52)

0.015 (0.38)

0.150

(3.81)

MIN

0.200 (5.08)

0.125 (3.18)

0.100

(2.54)

BSC

Mini-DIP (N-8) Package

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

Small Outline (R-8) Package

0.019 (0.48)

0.014 (0.36)

0.050

(1.27)

BSC

0.102 (2.59)

0.094 (2.39)

0.197 (5.01)

0.189 (4.80)

0.010 (0.25)

0.004 (0.10)

0.098 (0.2482)

0.075 (0.1905)

0.190 (4.82)

0.170 (4.32)

0.030 (0.76)

0.018 (0.46)

10

°

0

°

0.090

(2.29)

8

°

0

°

0.020 (0.051) x 45

°

CHAMF

1

8

5

4

PIN 1

0.157 (3.99)

0.150 (3.81)

0.244 (6.20)

0.228 (5.79)

0.150 (3.81)