AD847
REV. F
–12–
C1191f–10–9/92
PRINTED IN U.S.A.
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 kΩ 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
10µF
TO ANALOG
GROUND PLANE
0.1µF
–
+
1V NOMINAL
REFERENCE INPUT
10k
1k
100Ω
AD847
ANALOG GROUND PLANE
ANALOG
OUTPUT
ANALOG
SUPPLY
GROUND
0.1µF
10µF
–15V
+5V
1kΩ
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)
