AD7322 Analog Devices, AD7322 Datasheet - Page 32

• Manufacturer Part Number: AD7322
• Description: Software Selectable True Bipolar Input, 2-Channel, 12-Bit Plus Sign ADC
• Manufacturer: Analog Devices

Specifications of AD7322

• Resolution (bits): 13bit
• # Chan: 2
• Sample Rate: 1MSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Bip,Diff-Uni,SE-Uni
• Ain Range: Bip (Vref),Bip (Vref) x 2,Bip (Vref) x 4,Bip 10V,Bip 2.5V,Bip 5.0V,Uni (Vref) x 4,Uni 10V
• Adc Architecture: SAR
• Pkg Type: SOP

AD7322
APPLICATION HINTS
LAYOUT AND GROUNDING
The printed circuit board that houses the AD7322 should be
designed so that the analog and digital sections are confined to
certain areas of the board. This design facilitates the use of
ground planes that can easily be separated.
To provide optimum shielding for ground planes, a minimum
etch technique is generally best. All AGND pins on the AD7322
should be connected to the AGND plane. Digital and analog
ground pins should be joined in only one place. If the AD7322
is in a system where multiple devices require an AGND and
DGND connection, the connection should still be made at only
one point. A star point should be established as close as possible
to the ground pins on the AD7322.
Good connections should be made to the power and ground
planes. This can be done with a single via or multiple vias for
each supply and ground pin.
Avoid running digital lines under the AD7322 device because
this couples noise onto the die. However, the analog ground
plane should be allowed to run under the AD7322 to avoid
noise coupling. The power supply lines to the AD7322 device
should use as large a trace as possible to provide low impedance
paths and reduce the effects of glitches on the power supply line.
To avoid radiating noise to other sections of the board, com-
ponents with fast switching signals, such as clocks, should be
shielded with digital ground and never run near the analog inputs.
Avoid crossover of digital and analog signals. To reduce the effects
of feedthrough within the board, traces should be run at right
angles to each other. A microstrip technique is the best method,
but its use may not be possible with a double-sided board. In this
technique, the component side of the board is dedicated to ground
planes, and signals are placed on the other side.
Good decoupling is also important. All analog supplies should
be decoupled with 10 μF tantalum capacitors in parallel with
0.1 μF capacitors to AGND. To achieve the best results from
these decoupling components, they must be placed as close as
possible to the device, ideally right up against the device. The
0.1 μF capacitors should have a low effective series resistance
(ESR) and low effective series inductance (ESI), such as is
typical of common ceramic and surface-mount types of
capacitors. These low ESR, low ESI capacitors provide a low
impedance path to ground at high frequencies to handle
transient currents due to internal logic switching.
Rev. A | Page 32 of 36
POWER SUPPLY CONFIGURATION
If the supply voltage for the analog input circuitry is different
from that of the AD7322 V
input can be applied to the AD7322 before V
established, then it is recommended that Schottky diodes be
placed in series with the AD7322 V
Figure 53 shows this Schottky diode configuration. BAT43
Schottky diodes are used.
In an application where nonsymmetrical V
are being used, adhere to the following guidelines. Table 16
outlines the V
voltages when nonsymmetrical supplies are required. When
operating the AD7322 with low V
recommended that these supplies be symmetrical.
For the 0 V to 4 × V
minimum supply recommendations outlined in Table 6.
Table 16. Nonsymmetrical V
V
5 V
6 V
7 V
8 V
9 V
10 V to 16.5 V
DD
1
SS
ADDITIONAL PINS OMITTED FOR CLARITY.
supply range that can be used for particular V
Figure 53. Schottky Diode Connection
REF
V
V
range, V
IN
IN
0
1
DD
V
V
AD7322
V+
V–
Typical V
−5 V to −5.5 V
−5 V to −8.5 V
−5 V to −11.5 V
−5 V to −15 V
−5 V to −16.5 V
−5 V to −16.5 V
DD
SS
and V
DD
SS
3V/5V
and V
V
can be tied to AGND as per
DD
SS
CC
1
DD
DOUT
supplies or if the analog
SCLK
and V
SS
DIN
and V
CS
SS
Range
Requirements
DD
SS
DD
SS
voltages, it is
and V
and V
supply signals.
SS
SS
are
supplies
DD