Datasheet

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SBAS255C − JUNE 2004 − REVISED APRIL 2009
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17
Ncont Mode
Non-continuous (ncont) mode of operation is intended for
ranges 1 to 7. It is not recommended to use Range 0 when
operating in non-continuous mode. Figure 13 illustrates
operation in ncont mode. The integrations come in pairs
(that is, sides A/B or sides B/A) followed by a time during
which no integrations occur. During that time, the previous
integrations are being measured, reset and auto-zeroed.
Before the DDC114 can advance to states 3 or 6, both
sides A and B must be finished with the m/r/az cycle, which
takes time t
10
. When the m/r/az cycles are completed, time
t
11
is needed to prepare the next side for integration. This
time is required for ncont mode because the m/r/az cycle
of ncont mode is slightly different from that of cont mode.
After the first integration ends, DVALID
goes low in time t
8
.
This time is the same as in cont mode. The second data will
be ready in time t
9
after the first data is ready. One result
of the naming convention used in this data sheet is that
when the DDC114 is operating in ncont mode, it passes
through both ncont mode states and cont mode states. For
example, in Figure 13, the state pattern is 3, 4, 1, 2, 3, 4,
1, 2, 3, 4 ... where 3 and 4 are cont mode states. Ncont
mode, by definition, means that for some portion of the
time, neither side A nor B is integrating. States that perform
an integration are labeled cont mode states, while those
that do not are called ncont mode states. Since
integrations are performed in ncont mode, just not
continuously, some cont mode states must be used in an
ncont mode state pattern.
SYMBOL DESCRIPTION VALUE (CLK = 4MHz, CLK_4X = 0) VALUE (CLK = 4.8MHz, CLK_4X = 0)
t
8
1st ncont Mode Data Ready 344.75 ± 0.25µs 287.292 ± 0.208µs
t
9
2nd ncont Mode Data Ready 362.5µs 302.083µs
t
10
ncont Mode m/r/az Cycle 725.25 ± 0.25µs 604.375 ± 0.208µs
t
11
Prepare Side for Integration ≥ 18µs ≥ 15µs
Figure 13. Non-Continuous Mode Timing
23134 4 1 2
Int BInt AInt BInt A
m/r/az Bm/r/az A
m/r/az A m/r/az B
CONV
State
mbsy
m/r/az
Status
Integration
Status
DVALID
t
10
t
9
t
11
t
8
Side A
Data
Side B
Data
Side A
Data
Side B
Data