AD7570 Просмотр технического описания (PDF) - Analog Devices
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AD7570 Datasheet PDF : 12 Pages
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OPERATION GUIDELINES
UNIPOLAR BINARY OPERATION
ADJUSTMENT PROCEDURES UNIPOLAR OPERATION
Figure 10 shows the circuit connections required for unipolar
analog inputs. If positive analog inputs are to be quantized,
Gain Adjustment
1. Apply continuous start commands to the STRT input of the
t
VREF must be negative, and the OUT1 (pin 4) terminal of the
AD7570.
AD7570 must be connected to the "+" comparator input. For
negative analog inputs, VREF must be positive, and the OUT1
2. Apply full scale minus 1-1/2LSB to AIN.
terminal connected to the "-" input of the comparator.
3. Observe the S RO terminal as described under zero offset
For clarity, the digital control functions have been omitted
from the diagram. For proper use of the digital input/output
control functions, refer to the pin function description.
procedure above, and adjust the gain potentiometer (R4)
until the LSB flickers between 0 and I, and all other data
bits equal "I". An alternate method is to adjust VREF
instead of using R4.
The input voltage/output code relationship for unipolar
operation is shown in Table 2. Due to the inherent multiplying
vcc
VDD+5V TO +15V
+15V
capability of the internal D/A converter, the AD7570 can ac-
curately quantize full scale ranges of 10V to 1V. It should be
noted, however, that for smaller full scale ranges, the resolu-
tion and speed limitations of the comparator impose a
limitation on the maximum conversion rate.
BIPOLAR (OFFSET BINARY) OPERATION
~ Figure 11 shows the AD7570 configured for offset binary
O(modified 2's complement) operation. Input voltage/output
codes are shown in Table 3.
B Amplifier AI, in conjunction with resistors R1, R2, and R3,
S 0ffsets the bipolar analog input by full scale, and reduces its
gain by a factor of 2. The analog signal applied to the AIN
O terminal is, therefore, a unipolar signal of 0 to +V or 0 to -V,
LETE depending on the polarity of VREF'
~fJv
22
4 I oun
VREF. 2
R3
20011
AD7570
~N:ci"~~o~N
R4
3
GAI~kADJ I 23
+15V
R2
3k
NOTE:
IF POSITIVE VREF IS USED. THE ANALOG INPUT RANGE IS 0 TO -VREF. AND THE
COMPARATOR'S (-) INPUT SHOULD BE CONNECTED TO oun (PIN 4) OF THE
AD7570.
Figure 10. Unipolar Operation
VREF VDD
Vcc
-10V +15V +5V TO +15V
t
t
R2
20k
BIPOLAR
ANALOG
INPUT
+10V TO -10V
20k
R1
R3
R5
10k
200
+15V
2
VREFI
2
R5
22 4 rUT1lk
3
5 OUT2'
AD7570
AGND
3
7
COMP
R6
3k
t
A
NOTE: IF POSITIVE VREF IS USED, CONNECT MINUS INPUT OF COMPARATOR
TO oun (PIN 4) OF THE AD7570.
I
Figure 11. Bipolar Operation
-8-
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