AD847
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
+15V
(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.
C1191f–10–9/92
ANALOG
OUTPUT
ANALOG
SUPPLY
GROUND
0.1µF
10µF
–15V
100pF
+5V
1kΩ
10µF
TO ANALOG
GROUND PLANE
0.1µF
1
2
3
4
5
DIGITAL
INPUTS
MSB
V
CC
24
REFCOM 23
REFIN1 22
REFIN2 21
1V NOMINAL
+ REFERENCE INPUT
10k
1k
–
AD668
6
7
8
9
10
11
12 LSB
I
OUT
20
R
LOAD
19
ACOM 18
LCOM 17
IBPO 16
V
EE
15
100Ω
AD847
ANALOG GROUND PLANE
THCOM 14
VTH 13
Figure 27. High Speed DAC Buffer
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
Mini-DIP (N-8) Package
Cerdip (Q-8) Package
0.005 (0.13) MIN
0.055 (1.40) MAX
Small Outline (R-8) Package
0.150 (3.81)
8
PIN 1
1
0.39 (9.91) MAX
5
0.25
(6.35)
4
0.31
(7.87)
PIN 1
1
4
8
5
0.310 (7.87)
0.220 (5.59)
8
0.244 (6.20)
0.228 (5.79)
PIN 1
1
5
0.157 (3.99)
0.150 (3.81)
4
0.165±0.01
(4.19±0.25)
0.125
(3.18)
MIN
0.018±0.003
(0.46±0.08)
0.10
(2.54)
BSC
0.30 (7.62)
REF
0.033
(0.84)
NOM
0.035±0.01
(0.89±0.25)
0.200
(5.08)
MAX
0.200 (5.08)
0.125 (3.18)
0.405 (10.29) MAX
0.060 (1.52)
0.015 (0.38)
0.150
(3.81)
MIN
0.010 (0.25)
0.004 (0.10)
0.050
(1.27)
BSC
SEATING
PLANE
0.023 (0.58)
0.014 (0.36)
0.100 0.070 (1.78)
(2.54) 0.030 (0.76)
BSC
SEATING
PLANE
0.019 (0.48)
0.014 (0.36)
0.320 (8.13)
0.290 (7.37)
0.020 (0.051) x 45
°
CHAMF
0.190 (4.82)
0.170 (4.32)
8
°
0
°
10
°
0
°
0.098 (0.2482)
0.075 (0.1905)
0.090
(2.29)
0.011±0.003
(0.28±0.08)
15
°
0
°
0.015 (0.38)
0.008 (0.20)
15
°
0
°
0.030 (0.76)
0.018 (0.46)
All brand or product names mentioned are trademarks or registered trademarks of their respective holders.
–12–
REV. F
PRINTED IN U.S.A.
0.18±0.03
(4.57±0.76)
0.197 (5.01)
0.189 (4.80)
0.102 (2.59)
0.094 (2.39)
AD [ ANALOG DEVICES ]
