ad7531jd National Semiconductor Corporation, ad7531jd Datasheet - Page 4

• Manufacturer Part Number: ad7531jd
• Description: 10-bit, 12-bit Binary Multiplying D/a Converter
• Manufacturer: National Semiconductor Corporation

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Typical Applications
The following applications are also valid for 12-bit systems
using the DAC1220 and 2 additional digital inputs
Operational Amplifier Bias Current ( Figure 3 )
The op amp bias current I
feedback resistor BI-FET op amps have low I
fore the 15k
strongly recommended for the DAC1020 applications
V
The output impedance R
the digital input code which causes a modulation of the op-
erational amplifier output offset It is therefore recommend-
ed to adjust the op amp V
digital inputs are high R
is high and R
OS
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Op Amp Family
Considerations
LM741
LF357
LF356
LF351
c
OUT
I
b
error they introduce is negligible they are
approaches infinity if all inputs are low
OUT
OUT
OS
b
SELECTING AND COMPENSATING THE OPERATIONAL AMPLIFIER
10 pF
22 pF
24 pF
0
is E 45k if a single digital input
flows through the 15k internal
FIGURE 3 Basic Connection Unipolar or 2-Quadrant Multiplying
C
R
of the DAC is modulated by
F
OUT
is E 15k if more than 4
2 4k
V
0
where A
b
R
%
%
%
OUT
Configuration (Digital Attenuator)
s
10V
i
b
V
and there-
OUT s
e b
A
s
N
N
V
e
e
V
REF s
REF
b
0 if the A
1 if the A
1023
1024

25k
25k
10k
10k
10V
A1
P
2
V
a
N
REF
N
4
digital input is low
A2
digital input is high
4
a
Operational Amplifier V
Connect all digital inputs A1 – A10 to ground and adjust the
potentiometer to bring the op amp V
mV from ground potential If V
V
lution of the V
resistor between the inverting input of the op amp to
ground After V
Full-Scale Adjust ( Figure 4 )
Switch high all the digital inputs A1 – A10 and measure the
op amp output voltage Use a 500X potentiometer as
shown to bring
1023 1024
OS
A3
8
a
adjustment is required It is helpful to increase the reso-
V
V
V
V
V
W
a
a
b
b
  
1024
A10
J
OS
OS
ll
Circuit Settling
adjust procedure by connecting a 1 kX
has been adjusted remove the 1 kX
V
OUT
Time t
1 5 ms
40 ms
3 ms
4 ms
ll
OS
to a voltage equal to V
Adjust ( Figure 3 )
s
REF
is less than 10V a finer
OUT
pin to within
TL H 5689 – 3
Circuit Small
Signal BW
200 kHz
0 5M
0 5M
1M
REF c
g
1