AD1671S View Datasheet(PDF) - Analog Devices
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Description
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AD1671S Datasheet PDF : 16 Pages
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AD1671
Table III. Output Data Format
Input
Range
Coding
Analog
Inputl
Digital
Output
0 V to +2.5 V Straight Binary
≤ –0.0003 V
0V
+2.5 V
≥ +2.5003 V
0 V to +5 V
Straight Binary
≤ –0.0006 V
0V
+5 V
≥ +5.0006 V
–2.5 V to +2.5 V Offset Binary
≤ –2.5006 V
–2.5 V
+2.5 V
≥ +2.4994 V
–5 V to +5 V Offset Binary
≤ –5.0012 V
–5 V
+5 V
≥ +4.9988 V
–2.5 V to +2.5 V
Twos Complement
(Using MSB)
≤ –2.5006 V
–2.5 V
+2.5 V
≥ +2.4994 V
–5 V to +5 V
Twos Complement
(Using MSB)
≤ –5.0012 V
–5 V
+5 V
≥ +4.9988 V
0000 0000 0000
0000 0000 0000
1111 1111 1111
1111 1111 1111
0000 0000 0000
0000 0000 0000
1111 1111 1111
1111 1111 1111
0000 0000 0000
0000 0000 0000
1111 1111 1111
1111 1111 1111
0000 0000 0000
0000 0000 0000
1111 1111 1111
1111 1111 1111
1000 0000 0000
1000 0000 0000
0111 1111 1111
0111 1111 1111
1000 0000 0000
1000 0000 0000
0111 1111 1111
0111 1111 1111
NOTES
1Voltages listed are with offset and gain errors adjusted to zero.
2Typical performance.
OTR2
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
OUTPUT DATA FORMAT
The AD1671 provides both MSB and MSB outputs, delivering
data in positive true straight binary for unipolar input ranges
and positive true offset binary or twos complement for bipolar
input ranges. Straight binary coding is used for systems that ac-
cept positive-only signals. If straight binary coding is used with
bipolar input signals, a 0 V input would result in a binary output
of 2048. The application software would have to subtract 2048
to determine the true input voltage. Host registers typically per-
form math on signed integers and assume data is in that format.
Twos complement format minimizes software overhead which is
especially important in high speed data transfers, such as a
DMA operation. The CPU is not bogged down performing data
conversion steps, hence the total system throughput is increased.
OPTIONAL EXTERNAL REFERENCE
The AD1671 includes an onboard +2.5 V reference. The refer-
ence input pin (REF IN) can be connected to reference output
pin (REF OUT) or a standard external +2.5 V reference can be
selected to meet specific system requirements. Fast switching in-
put dependent currents are modulated at the reference input.
The reference input voltage can be held with the use of a capaci-
tor. To prevent the AD1671’s onboard reference from oscil-
lating when not connected to REF IN, REF OUT must be
connected to +5 V. It is possible to connect REF OUT to +5 V
due to its output circuit implementation which shuts down the
reference.
ILOGIC VS. CONVERSION RATE
Figure 15 is the typical logic supply current vs. conversion rate
for various capacitor loads on the digital outputs.
6.5
6.0
5.5
5.0
4.5
4.0
3.5
CL = 50pF
3.0
2.5
2.0
CL = 30pF
1.5
1.0
0.5
1k
10k
100k
CONVERSION RATE – Hz
CL = 0pF
1M
Figure 15. ILOGIC vs. Conversion Rate for Various
Capacitive Loads on the Digital Outputs
REV. B
–11–
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