Datasheet

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SBAS255C − JUNE 2004 − REVISED APRIL 2009
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23
RETRIEVAL BEFORE CONV TOGGLES
(CONTINUOUS MODE)
Data retrieval before CONV toggles is the most
straightforward method. Data retrieval begins soon after
DVALID
goes low and finishes before CONV toggles; as
shown in Figure 23. For best performance, data retrieval
must stop t
28
before CONV toggles. This method is most
appropriate for longer integration times. The maximum
time available for readback is T
INT
– t
27
– t
28
. For DCLK =
10MHz and CLK = 4MHz, the maximum number of
DDC114s that can be daisy-chained together (FORMAT =
high) is calculated by Equation 1:
T
INT
* 355.125ms
80t
DCLK
NOTE: 64τ
DCLK
is used for FORMAT = low.
where τ
DCLK
is the period of the data clock. For example,
if T
INT
= 1000µs and DCLK = 10MHz, the maximum
number of DDC114s (FORMAT = high) is shown in
Equation 2:
1000ms * 355.125ms
(
80
)(
100ns
)
+ 80.60 ³ 80 DDC114s
(or 100 for FORMAT = low).
SYMBOL
DESCRIPTION
CLK = 4MHz, CLK_4X = 0 CLK = 4.8MHz, CLK_4X = 0
UNITS
SYMBOL DESCRIPTION
MIN TYP MAX MIN TYP MAX
UNITS
t
27
Cont Mode Data Ready 345.00 ± 0.125 287.5 ± 0.104 µs
t
28
Data Retrieval Shutdown Before Edge of CONV 10 10 µs
Figure 23. Readback Before CONV Toggles
(1)
(2)
……
……
Side B
Data
Side A
Data
T
INT
T
INT
t
27
t
28
CONV
DVALID
DCLK
DOUT