DDC114IRTCT Datasheet, PDF (25/35 Pages) Texas Instruments – Quad Current Input, 20-Bit Analog-To-Digital Converter

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RETRIEVAL BEFORE AND AFTER CONV
TOGGLES (CONTINUOUS MODE)
For the absolute maximum time for data retrieval, data can
be retrieved before and after CONV toggles. Nearly all of
T_INT is available for data retrieval. Figure 25 illustrates how
this is done by combining the two previous methods. You
must pause the retrieval during CONV toggling to prevent
digital noise, as discussed previously, and finish before the
next data is ready. The maximum number of DDC114s that
can be daisy-chained together (FORMAT = high) is:
T_INT * 20ms * 1.75ms
80t_DCLK
NOTE: 64τ_DCLK is used for FORMAT = low.
For T_INT = 400µs and DCLK = 10MHz, the maximum
number of DDC114s is 47 (or 59 for FORMAT = low).
DDC114
SBAS255C − JUNE 2004 − REVISED APRIL 2009
RETRIEVAL: NONCONTINUOUS MODE
Retrieving in noncontinuous mode is slightly different than
compared with the continuous mode. As illustrated in
Figure 26, DVALID goes low in time t₃₀ after the first
integration completes. If T_INT is shorter than this time, all
of t₃₁ is available to retrieve data before the other side data
is ready. For T_INT > t₃₀, the first integration data is ready
before the second integration completes. Data retrieval
must be delayed until the second integration completes,
leaving less time available for retrieval. The time available
is t₃₁ – (T_INT – t₃₀). The second integration data must be
retrieved before the next round of integration begins. This
time is highly dependent on the pattern used to generate
CONV. As with the continuous mode, data retrieval must
halt before and after CONV toggles (t₂₈, t₂₉) and be
completed before new data is ready (t₂₆).
CONV
T_INT
T_INT
T_INT
DVALID
t₂₉
t₂₈
t₂₆
DCLK
…
…
…
…
…
…
DOUT
…
…
…
…
…
…
Side B
Data
SYMBOL DESCRIPTION
t₂₆
Hold Time that DOUT is Valid Before Falling Edge of DVALID
t₂₈
Data Retrieval Shutdown Before Edge of CONV
t₂₉
Data Retrieval Start-Up After Edge of CONV
Side A
Data
CLK = 4MHZ, CLK_4X = 0
MIN
TYP
MAX
1.75
10
10
CLK = 4.8MHZ, CLK_4X = 0
MIN
TYP
MAX
1.458
10
10
UNITS
µs
µs
µs
Figure 25. Readback Before and After CONV Toggles
CONV
T_{IN T}
T_INT
T_INT
T_INT
DVALID
t₃₀
DCLK
DOUT
SYMBOL DESCRIPTION
t₃₀
1st ncont Mode Data Ready
t₃₁
2nd ncont Mode Data Ready
t_{3 1}
…
…
…
…
Side A
Data
Side B
Data
CLK = 4MHz, CLK_4X = 0
MIN
TYP
MAX
344.75 ± 0.25
362.500
CLK = 4.8MHz, CLK_4X = 0
MIN
TYP
MAX
287.292 ± 0.208
302.083
Figure 26. Readback in Non-Continuous Mode
UNITS
µs
µs
25