DDC112_15 Datasheet, PDF (24/34 Pages) Texas Instruments – Dual Current Input 20-Bit ANALOG-TO-DIGITAL CONVERTER

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:
T_INT – 20µs – 2µs
40τ_DCLK
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 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’s data is ready. For T_INT > t₃₀, 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 t₃₁ – (T_INT – t₃₀). 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 (t₂₈ and t₂₉) and be
completed before new data is ready (t₂₆).
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.
CONV
DVALID
DXMIT
DCLK
DOUT
T_INT
t₂₈
T_INT
t₂₉
t₂₆
T_INT
•••
•••
•••
•••
•••
•••
•••
•••
•••
•••
•••
•••
Side B
Data
Side A
Data
SYMBOL
t₂₆
t₂₈
t₂₉
DESCRIPTION
Hold Time for DXMIT HIGH Before Falling
Edge of DVALID
Data Retrieval Shutdown Before Edge of CONV
Data Retrieval Start-Up After dge of CONV
CLK = 10MHz
MIN
TYP
MAX
2
10
10
CLK = 15MHz
MIN
TYP
MAX
1.33
10
10
UNITS
µs
µs
µs
FIGURE 26. Readback Before and After CONV Toggles.
24
DDC112
www.ti.com
SBAS085B