AD1376_15 Datasheet, PDF (7/12 Pages) Analog Devices – Complete, High Speed 16-Bit A/D Converters

In either adjustment circuit, the fixed resistor connected to
Pin 27 should be located close to this pin to keep the pin
connection short. Pin 27 is quite sensitive to external noise
pickup and should be guarded by ANALOG COMMON.
TIMING
The timing diagram is shown in Figure 8. Receipt of a
CONVERT START signal sets the STATUS flag, indicating
conversion in progress. This in turn removes the inhibit applied
to the gated clock, permitting it to run through 17 cycles. All
the SAR parallel bits, the STATUS flip-flops, and the gated clock
inhibit signal are initialized on the trailing edge of the
CONVERT START signal. At time t0, B1 is reset and B2–B16 are
set unconditionally. 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 that 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.
(1)
CONVERT
START
MAXIMUM THROUGHPUT TIME
CONVERSION TIME (2)
INTERNAL
CLOCK
STATUS
MSB
BIT 2
BIT 3
BIT 4
BIT 5
BIT 6
BIT 7
BIT 8
BIT 9
BIT 10
BIT 11
BIT 12
BIT 13
BIT 14
BIT 15
LSB
t₀ t₁ t₂ t₃ t₄ t₅ t₆ t₇ t₈ t₉ t₁₀ t₁₁ t₁₂ t₁₃ t₁₄ t₁₅ t₁₆
(2)
0
(3) t₁₇
1
1
0
0
1
1
1
0
1
1
1
1
0
MSB
1
0
01 1 0 01 1 10 1 1 1 1 0 1 0
LSB
NOTES:
1. THE CONVERT START PULSEWIDTH IS 50ns MIN AND MUST REMAIN LOW DURING A
CONVERSION. THE CONVERSION IS INITIATED BY THE TRAILING EDGE OF THE
CONVERT COMMAND.
2. MSB DECISION.
3. CLOCK REMAINS LOW AFTER LAST BIT DECISION.
Figure 8. Timing Diagram (Binary Code 0110011101111010)
AD1376/AD1377
DIGITAL OUTPUT DATA
Parallel 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 complement-
tary 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 9). Parallel data
output changes state on positive going clock edges.
BIT 16
VALID
BUSY
(STATUS)
20ns MIN TO 90ns
Figure 9. LSB Valid to Status Low
Short Cycle Input
Pin 32 (SHORT CYCLE) permits the timing cycle shown in
Figure 8 to be terminated after any number of desired bits has
been converted, allowing somewhat shorter conversion times in
applications not requiring full 16-bit resolution. When 10-bit
resolution is desired, Pin 32 is connected to Bit 11 output
Pin 11. The conversion cycle then terminates and the STATUS
flag resets after the Bit 10 decision (Figure 8). Short cycle
connections and associated 8-, 10-, 12-, 13-, 14-, and 15-bit
conversion times are summarized in Table 3 for a 1.6 MHz
clock (AD1377) or 933 kHz clock (AD1376).
Table 3. Short Cycle Connections
Resolution
(%
Bits FSR)
Maximum
Conversion Time (µs)
AD1377 AD1376
Status
Flag
Reset
16 0.0015 10
17.1
t16
15 0.003 9.4
16.1
t15
14 0.006 8.7
15.0
t1
13 0.012 8.1
13.9
t13
12 0.024 7.5
12.9
t12
10 0.100 6.3
10.7
t10
8 0.390 5.0
8.6
t8
Connect
Short Cycle
Pin 32 to
NC (Open)
Pin 16
Pin 15
Pin 14
Pin 13
Pin 11
Pin 9
INPUT SCALING
The ADC inputs should be scaled as close to the maximum
input signal range as possible to use the maximum signal
resolution of the ADC. Connect the input signal as shown in
Table 4. See Figure 10 for circuit details.
Rev. D | Page 7 of 12