Datasheet

Data Sheet AD7327
Rev. B | Page 19 of 36
TYPICAL CONNECTION DIAGRAM
Figure 32 shows a typical connection diagram for the AD7327.
In this configuration, the AGND pin is connected to the analog
ground plane of the system, and the DGND pin is connected to
the digital ground plane of the system. The analog inputs on the
AD7327 can be configured to operate in single-ended, true
differential, or pseudo differential mode. The AD7327 can operate
with either an internal or external reference. In Figure 32, the
AD7327 is configured to operate with the internal 2.5 V reference.
A 680 nF decoupling capacitor is required when operating with
the internal reference.
The V
CC
pin can be connected to either a 3 V supply voltage or a
5 V supply voltage. The V
DD
and V
SS
are the dual supplies for the
high voltage analog input structures. The voltage on these pins
must be equal to or greater than the highest analog input range
selected on the analog input channels (see Table 6). The V
DRIVE
pin is connected to the supply voltage of the microprocessor.
The voltage applied to the V
DRIVE
input controls the voltage of
the serial interface. V
DRIVE
can be set to 3 V or 5 V.
AD7327
V
CC
V
DD
1
SERIAL
INTERFACE
µC/µP
V
IN
0
V
IN
1
V
IN
2
V
IN
3
V
IN
4
V
IN
5
V
IN
6
V
IN
7
REFIN/OUT
CS
DOUT
V
DRIVE
SCLK
DIN
DGND
10µF 0.1µF
+
10µF0.1µF
+
10µF0.1µF
+
ANALOG INPUTS
±10V, ±5V, ±2.5V
0V TO +10V
+15
V
–15V
680nF
V
SS
1
V
CC
+2.7
V
TO 5.25
V
1
MINIMUM V
DD
AND V
SS
SUPPLY VOLTAGES
DEPEND ON THE HIGHEST ANALOG INPUT
RANGE SELECTED.
AGND
10µF 0.1µF
+
+3V SUPPLY
05401-025
Figure 32. Typical Connection Diagram
ANALOG INPUT
Single-Ended Inputs
The AD7327 has a total of eight analog inputs when operating
the AD7327 in single-ended mode. Each analog input can be
independently programmed to one of the four analog input
ranges. In applications where the signal source is high impedance,
it is recommended to buffer the signal before applying it to the
ADC analog inputs. Figure 33 shows the configuration of the
AD7327 in single-ended mode.
AD7327
1
V
IN
+
V
+
V–
V
DD
V
SS
V
CC
5V
AGND
1
ADDITIONAL PINS OMITTED FOR CLARITY.
05401-026
Figure 33. Single-Ended Mode Typical Connection Diagram
True Differential Mode
The AD7327 can have a total of four true differential analog
input pairs. Differential signals have some benefits over single-
ended signals, including better noise immunity based on the
common-mode rejection of the device and improvements in
distortion performance. Figure 34 defines the configuration of
the true differential analog inputs of the AD7327.
AD7327
1
V
IN
+
V
IN
–
1
ADDITIONAL PINS OMITTED FOR CLARITY.
05401-027
Figure 34. True Differential Inputs
The amplitude of the differential signal is the difference
between the signals applied to the V
IN
+ and V
IN
− pins in
each differential pair (V
IN
+ − V
IN
−). V
IN
+ and V
IN
− should
be simultaneously driven by two signals each of amplitude
±4 × V
REF
(depending on the input range selected) that are
180° out of phase. Assuming the ±4 × V
REF
mode, the amplitude
of the differential signal is −20 V to +20 V p-p (2 × 4 × V
REF
),
regardless of the common mode.
The common mode is the average of the two signals
(V
IN
+ + V
IN
−)/2
and is, therefore, the voltage on which the two input signals are
centered.
This voltage is set up externally, and its range varies with reference
voltage. As the reference voltage increases, the common-mode
range decreases. When driving the differential inputs with an
amplifier, the actual common-mode range is determined by the
output swing of the amplifier. If the differential inputs are not
driven from an amplifier, the common-mode range is determined
by the supply voltage on the V
DD
and the V
SS
supply pins.
When a conversion takes place, the common mode is rejected,
resulting in a noise-free signal of amplitude −2 × (4 × V
REF
) to +2 ×
(4 × V
REF
) corresponding to digital Code −4096 to Code +4095.