AD847
H IGH SP EED D AC BUFFER
(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.
T he 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. T he
output voltage is determined by the amplifier’s feedback resistor
+15V
10µF
TO ANALOG
GROUND PLANE
0.1µF
1
2
3
MSB
V
24
CC
–
REFCOM 23
1V NOMINAL
REFERENCE INPUT
22
21
20
19
+
REFIN1
REFIN2
10k
4
5
1k
I
OUT
100Ω
DIGITAL
INPUTS
AD668
ANALOG
OUTPUT
6
R
LOAD
AD847
ANALOG GROUND PLANE
7
ACOM 18
ANALOG
SUPPLY
GROUND
8
17
16
LCOM
IBPO
9
10µF
0.1µF
–15V
+5V
10
11
15
14
V
EE
THCOM
VTH
100pF
12 LSB
13
1kΩ
Figure 27. High Speed DAC Buffer
O UTLINE D IMENSIO NS
D imensions shown in inches and (mm).
Sm all O utline (R-8) P ackage
Mini-D IP (N-8) P ackage
Cerdip (Q-8) P ackage
0.150 (3.81)
0.005 (0.13) MIN
0.055 (1.40) MAX
5
8
5
0.25
(6.35)
0.31
(7.87)
8
PIN 1
8
5
0.244 (6.20)
0.228 (5.79)
0.157 (3.99)
0.150 (3.81)
0.310 (7.87)
1
4
PIN 1
0.220 (5.59)
PIN 1
1
1
4
4
0.39 (9.91) MAX
0.035±0.01
(0.89±0.25)
0.405 (10.29) MAX
0.165±0.01
(4.19±0.25)
0.060 (1.52)
0.015 (0.38)
0.197 (5.01)
0.189 (4.80)
0.200
(5.08)
MAX
0.18±0.03
(4.57±0.76)
0.125
(3.18)
MIN
0.102 (2.59)
0.094 (2.39)
0.010 (0.25)
0.004 (0.10)
0.150
(3.81)
MIN
0.200 (5.08)
0.125 (3.18)
0.019 (0.48)
0.014 (0.36)
0.050
(1.27)
BSC
0.018±0.003
(0.46±0.08) (2.54)
0.10
0.033
(0.84)
NOM
SEATING
PLANE
BSC
0.023 (0.58) 0.100
0.070 (1.78)
0.030 (0.76)
0.020 (0.051) x 45
CHAMF
°
SEATING
PLANE
(2.54)
BSC
0.30 (7.62)
REF
0.014 (0.36)
0.190 (4.82)
0.170 (4.32)
0.320 (8.13)
0.290 (7.37)
8
°
0.090
(2.29)
0°
10
0°
°
0.011±0.003
(0.28±0.08)
0.030 (0.76)
0.018 (0.46)
0.098 (0.2482)
0.075 (0.1905)
0.015 (0.38)
0.008 (0.20)
15°
0°
15°
0°
All brand or product nam es m entioned are tradem arks or registered tradem arks of their respective holders.
–12–
REV. F
ADI [ ADI ]
