Datasheet

DDC112
22
SBAS085B
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RETRIEVAL BEFORE CONV TOGGLES
(CONTINUOUS MODE)
This is the most straightforward method. Data retrieval be-
gins soon after DVALID
goes LOW and finishes before
CONV toggles, see Figure 24. For best performance, data
retrieval must stop t
28
before CONV toggles. This method is
the most appropriate for longer integration times. The maxi-
mum time available for readback is T
INT
– t
27
– t
28
.
For DCLK and CLK = 10MHz, the maximum number of
DDC112s that can be daisy-chained together is:
Ts
INT
DCLK
– .431 2
40
µ
τ
Where τ
DCLK
is the period of the data clock. For example, if
T
INT
= 1000µs and DCLK = 10MHz, the maximum number of
DDC112s is:
1000 431 2
40 100
142 2 142 112
µµ
=→
ss
ns
DDC s
– .
()( )
.
RETRIEVAL AFTER CONV TOGGLES
(CONTINUOUS MODE)
For shorter integration times, more time is available if data
retrieval begins after CONV toggles and ends before the new
data is ready. Data retrieval must wait t
29
after CONV toggles
before beginning. Figure 25 shows an example of this. The
maximum time available for retrieval is t
27
– t
29
– t
26
(421.2µs – 10µs – 2µs for CLK = 10MHz), regardless of T
INT
.
The maximum number of DDC112s that can be daisy-
chained together is:
409 2
40
. µs
DCLK
τ
For DCLK = 10MHz, the maximum number of DDC112s is
102.
FIGURE 23. Timing Diagram When Using the DIN Function of the DDC112.
t
18
t
14
t
20
t
21
t
22
t
23
t
24
t
25
Output Disabled
Output Enabled
Output Disabled
CLK
DVALID
DXMIT
DCLK
(1)
DIN
Input A
Bit 1
Input E
Bit 20
Input F
Bit 1
Input F
Bit 20
MSB
Output Disabled
Output Enabled
LSB LSB Output DisabledMSB
DOUT
NOTE: (1) Disable DCLK (preferably LOW) when DXMIT is HIGH.
t
26
t
22A,
t
22B
TABLE X. Timing for the DDC112 Data Retrieval Using DIN.
CLK = 10MHz CLK = 15MHz
SYMBOL DESCRIPTION MIN TYP MAX MIN TYP MAX UNITS
t
24
Set-Up Time From DIN to Rising Edge of DCLK 10 5 ns
t
25
Hold Time For DIN After Rising Edge of DCLK 10 10 ns
t
26
Hold Time for DXMIT HIGH Before Falling 2 1.33 µs
Edge of DVALID