Datasheet

DDC112
24
SBAS085B
www.ti.com
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 26 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 DDC112s that can
be daisy-chained together is:
Tss
INT
DCLK
––20 2
40
µµ
τ
For T
INT
= 500µs and DCLK = 10MHz, the maximum number
of DDC112s is 119.
RETRIEVAL: NONCONTINUOUS MODE
Retrieving in noncontinuous mode is slightly different as
compared with the continuous mode. As shown in Figure 27
and described in detail in Application Bulletin SBAA024
(available for download at www.ti.com), DVALID
goes LOW
in time t
30
after the first integration completes. If T
INT
is
shorter than this time, all of t
31
is available to retrieve data
before the other side’s data is ready. For T
INT
> t
30
, the first
integration’s 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 t
31
– (T
INT
– t
30
). The second integration’s
data must be retrieved before the next round of integrations
begin. 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 (t
28
and t
29
) and be
completed before new data is ready (t
26
).
POWER-UP SEQUENCING
Prior to power-up, all digital and analog input pins must be
LOW. At the time of power-up, these signal inputs can be
biased to a voltage other than 0V, however, they should
never exceed AV
DD
or DV
DD
. The level of CONV at power-
up is used to determine which side (A or B) will be integrated
first. Before integrations can begin though, CONV must
toggle; see Figure 28.
••• ••• ••• ••• ••• •••
••• ••• •••
••• ••• •••
DCLK
DXMIT
DVALID
CONV
DOUT
Side B
Data
Side A
Data
T
INT
t
29
t
28
t
26
T
INT
T
INT
FIGURE 26. Readback Before and After CONV Toggles.
CLK = 10MHz CLK = 15MHz
SYMBOL DESCRIPTION MIN TYP MAX MIN TYP MAX UNITS
t
26
Hold Time for DXMIT HIGH Before Falling 2 1.33 µs
Edge of DVALID
t
28
Data Retrieval Shutdown Before Edge of CONV 10 10 µs
t
29
Data Retrieval Start-Up After dge of CONV 10 10 µs