DDC101U Datasheet, PDF (24/29 Pages) Texas Instruments – 20-BIT ANALOG-TO-DIGITAL CONVERTER

–5VDC
10µF
Reference Buffer Bypass
+5VDC
0.1µF
Analog Input
Guard
10µF
0.1µF
1 V_S– , ANALOG
2 ANALOG COMMON
3 ANALOG INPUT
24
23
V_REF
22
10µF
4 ANALOG COMMON 21
5 V_S+, ANALOG
20
6 V_S+, ANALOG
19
7
18
8
17
10Ω
9
16
10
15
0.1µF
11
12 V_DD+, DIGITAL
14
13 ^{DIGITAL GROUND}
24-Lead SOIC
Top view
Analog Common
Digital Common
10µF
1kΩ
Reference
Noise Filter
REF1004 –2.5
–2.5V
25kΩ
Reference
Bias
Resistor
V_S–
FIGURE 24. Example of Basic DDC101 Circuit Connections.
Reading Data Output
Data from the previous conversion can be read any time after
the DATA VALID output is activated and before the end of
the next conversion. Data is held in an internal serial shift
register until the end of the next conversion. The data must
be completely read before the end of the next conversion or
it will be overwritten with new data.
Recommended Setup
The following Setup parameters are recommended, in gen-
eral, for use with the DDC101 with integration times of 1ms
or longer. Multiple integrations per conversion, where prac-
tical, will provide lowest noise as illustrated in the typical
performance curves.
Measurement Time Calculation
FUNCTION
Acquisition Clocks, K
Oversamples, M
CDS
RECOMMENDED
16
128
Enabled
A Continuous Integration Cycle consists of the Acquisition
Time, Initial Data Point Collection, Tracking Interval, and
Final Data Point Collection. The user can select these
functions as illustrated in Table XV.
The time between “Final Data point Start” commands is the
Integration Time, T_INT. The Measurement Time, T_MEAS, is the
Integration time reduced by the Acquisition Time and by the
Oversampling Time, T_OS.
T_MEAS = T_INT - T_ACQ - T_OS.
When CDS is used; T_OS, the oversampling time, is the time
required to collect a data point (M clock periods). Each
group of samples is averaged with the result at the midpoint
of each sample group. Therefore, with CDS, T_OS = M clock
periods. This is shown in Figure 25.
Two calculations of the Measurement Time are shown
FUNCTION
CLOCK CYCLES
USER
CONTROLLED
Acquisition Time, K
1, 16, 32
Yes
Initial Data Point
Samples, M⁽¹⁾
1, 2, 4, 8, 16, 32,64, 128, 256
Yes
Tracking Interval
Variable
Yes
Final Data Point
Samples, M⁽¹⁾
1, 2, 4, 8, 16, 32, 64, 128, 256
Yes
NOTE: (1) Will be the same in CDS mode, initial Data Point Samples = 0 in non-
CDS mode.
TABLE XV. Components of Integration Cycle.
®
DDC101
24