Datasheet

AD7264 Data Sheet
Rev. B | Page 18 of 28
10µF
1
100nF
V
DRIVE
V
DRIVE
V
DRIVE
3V OR 5V
SUPPLY
MICROPROCESSOR/
MICROCONTROLLER
10µF
1
COMPARATOR
SUPPLY 3V TO 5V
2
BOTH
COMPARATORS
AND ADCs
POWERED ON
100nF
100nF
100nF
ANALOG
SUPPLY
+5V
10µF
1
100nF
100nF
100nF
100nF
100nF
C
C+
C
C–
C
D+
C
D–
C
B–
C
B+
C
A–
C
A+
C
OUT
D
C
OUT
C
C
OUT
B
C
OUT
A
V
DRIVE
G0
G1
G2
G3
SCLK
D
OUT
A
D
OUT
B
REFSEL
CAL
PD0/D
IN
PD1
PD2
13 14 15 16 45 46 47 48 25 26 29 30
22
23
06732-027
36
24
32
35
34
37
38
39
40
27
31
21
1µF
1µF
C
C–
C
D–
GND
C
A–
C
B–
GND
C
C–
C
D
V
CC
C
A–
C
B
V
CC
AGND AGND AGND AGND AGND DGND
AV
CC
AV
CC
AV
CC
AV
CC
AV
CC
AV
CC
17 44 5 6 8 19 42 28 2 7 11 20 41 12 1 33
V
B–
V
B+
V
REF
B
V
REF
A
V
A+
V
A–
10
9
18
43
4
3
AD7264
V
DRIVE
V
DRIVE
FAST PROPAGATION DELAY
COMPARATOR INPUTS
1
THESE CAPACITORS ARE PLACED AT THE SUPPLY SOURCE AND MAY NOT BE REQUIRED IN ALL SYSTEMS.
2
THIS SUPPLY CAN BE CONNECTED TO THE ANALOG 5V SUPPLY IF REQUIRED.
LOW POWER
COMPARATOR INPUTS
SERIAL
INTERFACE
GAIN 2
SETUP
V
A–
AND V
A+
CONNECT
DIRECTLY
TO SENSOR
OUTPUTS
THIS REFERENCE SIGNAL
MUST BE BUFFERED
BEFORE IT CAN BE
USED ELSEWHERE IN
THE CIRCUIT
GAIN 2
GAIN 2
GAIN 2
GAIN 2
V
B–
AND V
B+
CONNECT
DIRECTLY
TO SENSOR
OUTPUTS
CS
3.125V
2.500V
1.875V
3.125V
2.500V
1.875V
3.125V
2.500V
1.875V
3.125V
2.500V
1.875V
Figure 27. Typical Connection Diagram for the AD7264 in Pin Driven Mode with Gain of 2 and Both ADCs and Comparators Fully Powered On
Comparator Application Details
The comparators on the AD7264 have been designed with no
internal hysteresis, allowing users the flexibility to add external
hysteretic if required for systems operating in noisy environments.
If the comparators on the AD7264 are used with external hyste-
resis, some external resistors and capacitors are required, as
shown in Figure 28. The value of R
F
and R
S
, the external resistors,
can be determined using the following equation, depending on
the amount of hysteresis required in the application:
CC
X
F
S
S
HYS
VCC
RR
R
V _
X
×
+
=
where C
X
_C
X
V
CC
= C
A
_C
B
V
CC
or C
C
_C
D
V
CC
.
The amount of hysteresis chosen must be sufficient to eliminate
the effects of analog noise at the comparator inputs, which may
affect the stability of the comparator outputs. The level of
hysteresis required in any system depends on the noise in the
system; thus, the value of R
F
and R
S
needs to be carefully selected
to eliminate any noise effects. To increase the level of hysteresis in
the system, increase the value of R
S
or R
F
. For example, R
F
= 10 MΩ,
R
S
= 1 kΩ gives 330 μV of hysteresis with a C
x
_C
x
V
CC
of 3.3 V; if
hysteresis is increased to 1 mV, R
S
= 3.1 kΩ. In certain applications,
a load capacitor (100 pF) may be required on the comparator
outputs to suppress high frequency transient glitches.