ADC0803(2002) データシートの表示（PDF） - Intersil
部品番号
コンポーネント説明
メーカー
ADC0803 Datasheet PDF : 17 Pages
| |||
ADC0803, ADC0804
Such an adjusted reference voltage can accommodate a
reduced span or dynamic voltage range of the analog input
voltage. If the analog input voltage were to range from 0.5V to
3.5V, instead of 0V to 5V, the span would be 3V. With 0.5V
applied to the VlN(-) pin to absorb the offset, the reference
voltage can be made equal to 1/2 of the 3V span or 1.5V. The
A/D now will encode the VlN(+) signal from 0.5V to 3.5V with
the 0.5V input corresponding to zero and the 3.5V input
corresponding to full scale. The full 8 bits of resolution are
therefore applied over this reduced analog input voltage
range. The requisite connections are shown in Figure 13. For
expanded scale inputs, the circuits of Figures 14 and 15 can
be used.
V+
(VREF) 20
R
VREF/2
9
DIGITAL
CIRCUITS
VIN ± 10V
5V
(VREF)
R
2R
6
20
VIN(+) V+
+
ADC0803-
10µF
2R
ADC0804
7 VIN(-)
FIGURE 14. HANDLING ±10V ANALOG INPUT RANGE
VIN ±5V
5V
(VREF)
R
R
6
20
VIN(+) V+
+
ADC0803-
10µF
ADC0804
7 VIN(-)
R
DECODE
ANALOG
CIRCUITS
AGND 8
DGND 10
FIGURE 12. THE VREFERENCE DESIGN ON THE IC
VREF
(5V)
ICL7611 5V
FS
“SPAN”/2
-
+
ADJ.
300
0.1µF
ZERO SHIFT VOLTAGE
TO VREF/2
TO VIN(-)
FIGURE 13. OFFSETTING THE ZERO OF THE ADC080X AND
PERFORMING AN INPUT RANGE (SPAN)
ADJUSTMENT
10
FIGURE 15. HANDLING ±5V ANALOG INPUT RANGE
Reference Accuracy Requirements
The converter can be operated in a pseudo-ratiometric mode
or an absolute mode. In ratiometric converter applications,
the magnitude of the reference voltage is a factor in both the
output of the source transducer and the output of the A/D
converter and therefore cancels out in the final digital output
code. In absolute conversion applicatIons, both the initial
value and the temperature stability of the reference voltage
are important accuracy factors in the operation of the A/D
converter. For VREF/2 voltages of 2.5V nominal value, initial
errors of ±10mV will cause conversion errors of ±1 LSB due
to the gain of 2 of the VREF/2 input. In reduced span
applications, the initial value and the stability of the VREF/2
input voltage become even more important. For example, if
the span is reduced to 2.5V, the analog input LSB voltage
value is correspondingly reduced from 20mV (5V span) to
10mV and 1 LSB at the VREF/2 input becomes 5mV. As can
be seen, this reduces the allowed initial tolerance of the
reference voltage and requires correspondingly less
absolute change with temperature variations. Note that
spans smaller than 2.5V place even tighter requirements on
the initial accuracy and stability of the reference source.
In general, the reference voltage will require an initial
adjustment. Errors due to an improper value of reference
voltage appear as full scale errors in the A/D transfer
Share Link: 