AD7324 Analog Devices, AD7324 Datasheet - Page 33

• Manufacturer Part Number: AD7324
• Description: Software Selectable True Bipolar Input, 4-Channel, 12-Bit Plus Sign A/D Converter
• Manufacturer: Analog Devices

Specifications of AD7324

• Resolution (bits): 13bit
• # Chan: 4
• 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

APPLICATION HINTS
LAYOUT AND GROUNDING
The printed circuit board that houses the AD7324 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 AD7324
should be connected to the AGND plane. Digital and analog
ground pins should be joined in only one place. If the AD7324
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 AD7324.
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 AD7324 device because
this couples noise onto the die. However, the analog ground
plane should be allowed to run under the AD7324 to avoid
noise coupling. The power supply lines to the AD7324 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, compo-
nents, such as clocks, with fast switching signals 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 33 of 36
POWER SUPPLY CONFIGURATION
If the supply voltage for the analog input circuitry is different to
that of the AD7324 V
could be applied to the AD7324 before V
then it is recommended that Schottky diodes are placed in series
with the AD7324 V
this Schottky diode configuration. BAT43 Schottky diodes are used.
In an application where non-symmetrical V
are being used, adhere to the following guidelines. Table 16
outlines the V
voltages when non-symmetrical supplies are required. When
operating the AD7324 with low V
recommended that these supplies be symmetrical.
Table 16. Non-Symmetrical V
V
5 V
6 V
7 V
8 V
9 V
10 V to 16.5 V
For the 0 to 4 × V
minimum supply recommendations outlined in Table 6.
DD
SS
1
ADDITIONAL PINS OMITTED FOR CLARITY.
supply range that can be used for particular V
Figure 54. Schottky Diode Connection
REF
DD
DD
range, V
and V
and V
V
V
V
V
IN
IN
IN
IN
0
1
2
3
AD7324
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
SS
DD
SS
SS
V
V–
supply signals. Figure 54 shows
supplies or if the analog input
SS
3V/5V
DD
can be tied to AGND as per
V
CC
DOUT
SCLK
DD
and V
1
DIN
CS
and V
SS
DD
Range
SS
and V
Requirements
SS
DD
voltages, it is
and V
SS
are established
AD7324
SS
supplies
DD