DDC264 Datasheet, PDF (19/26 Pages) Texas Instruments – 64-Channel, Current-Input Analog-to-Digital Converter

DDC264
www.ti.com
Retrieval After CONV Toggles
For shorter integration times, more time is available if
data retrieval begins after CONV toggles and ends
before the new data are ready. Data retrieval must
wait t_SDCV after CONV toggles before beginning. See
Figure 31 for an example of this timing sequence.
The maximum time available for retrieval is t_DR –
(t_SDCV + t_HDDODV), regardless of t_INT. The maximum
number of DDC264s that can be daisy-chained
together with Format = 1 is calculated by Equation 3:
274ms
(20 ´ 64)t_DCLK
(3)
NOTE: (16 × 64)τ_DCLK is for Format = 0.
For DCLK = 20MHz, the maximum number of
DDC264s is four (or five for Format = 0).
SBAS368C – MAY 2006 – REVISED JULY 2011
Retrieval Before and After CONV Toggles
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 32 illustrates how this process is done by
combining the two previous methods. Pause the
retrieval during CONV toggling to prevent digital
noise, as discussed previously, and finish before the
next data are ready. The maximum number of
DDC264s that can be daisy-chained together with
Format = 1 is:
t_INT - (t_SDCV + t_SDCV + t_HDDODV)
(20 ´ 64)t_DCLK
(4)
NOTE: (16 × 64)τ_DCLK is used for Format = 0.
For t_INT = 400μs and DCLK = 20MHz, the maximum
number of DDC264s is six (or seven for Format = 0).
CONV
t_INT
t_INT
t_INT
DVALID
t_DR
t_SDCV
t_HDDODV
DCLK
¼
¼
¼
DOUT
¼
Side A
Data
¼
Side B
Data
¼
Side A
Data
Figure 31. Readback After CONV Toggles
CONV
DVALID
DCLK
DOUT
t_INT
t_SDCV
¼
¼
t_INT
t_SDCV
¼
t_HDDODV
¼
t_INT
¼
¼
¼
¼
¼
¼
¼
¼
Side B
Data
Side A
Data
Figure 32. Readback Before and After CONV Toggles
Copyright © 2006–2011, Texas Instruments Incorporated
19