AD1380 Просмотр технического описания (PDF) - Analog Devices
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AD1380 Datasheet PDF : 8 Pages
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AD1380
SAR parallel bits, STATUS flip-flops and the gated clock in-
hibit signal are initialized on the trailing edge of the CONVERT
START signal. At time t0, B1 is reset and B2 – B16 are set un-
conditionally. At t1 the Bit 1 decision is made (keep) and Bit 2 is
reset unconditionally. This sequence continues until the Bit 16
(LSB) decision (keep) is made at t16. The STATUS flag is reset,
indicating that the conversion is complete and the parallel
output data is valid. Resetting the STATUS flag restores the
gated clock inhibit signal, forcing the clock output to the low
Logic “0” state. Note that the clock remains low until the next
conversion.
Corresponding parallel data bits become valid on the same
positive-going clock edge.
Figure 7. Clock High to Serial Out Valid
INPUT SCALING
The AD1380 inputs should be scaled as close to the maximum
input signal range as possible in order to utilize the maximum
signal resolution of the A/D converter. Connect the input signal
as shown in Table I. See Figure 8 for circuit details.
DIGITAL OUTPUT DATA
Both parallel and serial data from TTL storage registers is in
negative true form (Logic “1” = 0 V and Logic “0” = 2.4 V).
Parallel data output coding is complementary binary for unipolar
ranges and complementary offset binary for bipolar ranges.
Parallel data becomes valid at least 20 ns before the STATUS
flag returns to Logic “0,” permitting parallel data transfer to be
clocked on the “1” to “0” transition of the STATUS flag (see
Figure 6).
Figure 8. AD1380 Input Scaling Circuit
Figure 6. LSB Valid to Status Low
Serial data coding is complementary binary for unipolar input
ranges and complementary offset binary for bipolar input
ranges. Serial output is by bit (MSB first, LSB last) in NRZ
(non-return-to-zero) format. Serial and parallel data outputs
change state on positive-going clock edges. Serial data is guaran-
teed valid 120 ns after the rising clock edges, permitting serial
data to be clocked directly into a receiving register on the
negative-going clock edges as shown in Figure 7. There are 17
negative-going clock edges in the complete 16-bit conversion
cycle. The first negative edge shifts an invalid bit into the regis-
ter, which is shifted out on the last negative-going clock edge.
All serial data bits will have been correctly transferred and be in
the receiving shift register locations shown at the completion of
the conversion period.
Table I. AD1380 Input Scaling Connections
Input
Signal
Line
Connect Connect
Output Pin 4
Pin 7
Code to Pin to
Connect
Input
Signal to
± 10 V
COB 5
±5 V
COB 5
± 2.5 V
COB 5
0 V to +5 V CSB NC
0 V to +10 V CSB NC
Input Signal 7
Open
6
Pin 5
6
Pin 5
6
Open
6
NOTE
Pin 5 is extremely sensitive to noise and should be guarded by analog common.
REV. B
–5–
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