Datasheet

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SBAS325B − JUNE 2004 − REVISED APRIL 2009
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17
Ncont Mode
Non-continuous 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 the 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 DDC118 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 the ncont mode
because the m/r/az cycle of the ncont mode is slightly
different from that of the cont mode. After the first
integration ends, DVALID
goes low in time t
8
. This time is
the same as in the 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
DDC118 is operating in the 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 the ncont mode, just not
continuously, some cont mode states must be used in a
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