AD7608 Analog Devices, AD7608 Datasheet - Page 30

• Manufacturer Part Number: AD7608
• Description: 8-Channel DAS with 18-Bit, Bipolar, Simultaneous Sampling ADC
• Manufacturer: Analog Devices

Specifications of AD7608

• Resolution (bits): 18bit
• # Chan: 8
• Sample Rate: 200kSPS
• Interface: Par,Ser,SPI
• Analog Input Type: Diff-Bip
• Ain Range: Bip 10V,Bip 5.0V
• Adc Architecture: SAR
• Pkg Type: QFP

AD7608
Data Sheet
LAYOUT GUIDELINES
The printed circuit board that houses the AD7608 should be
designed so that the analog and digital sections are separated
and confined to different areas of the board.
Use at least one ground plane. It can be common or split between
the digital and analog sections. In the case of the split plane, the
digital and analog ground planes should be joined in only one
place, preferably as close as possible to the AD7608.
If the AD7608 is in a system where multiple devices require
analog-to-digital ground connections, the connection should
still be made at only one point: a star ground point should be
established as close as possible to the AD7608. Good connections
should be made to the ground plane. Avoid sharing one connec-
tion for multiple ground pins. Individual vias or multiple vias to
Figure 59. Top Layer Decoupling REFIN/REFOUT, REFCAPA, REFCAPB, and
the ground plane should be used for each ground pin.
REGCAP Pins
Avoid running digital lines under the devices because doing so
couples noise onto the die. Allow the analog ground plane to
run under the AD7608 to avoid noise coupling. Fast switching
signals like CONVST A, CONVST B, or clocks should be shielded
with digital ground to avoid radiating noise to other sections of
the board, and they should never run near analog signal paths.
Avoid crossover of digital and analog signals. Run traces on
layers in close proximity on the board at right angles to each
other to reduce the effect of feedthrough through the board.
The power supply lines to the AV
and V
pins on the
CC
DRIVE
AD7608 should use as large a trace as possible to provide
low impedance paths and reduce the effect of glitches on the
power supply lines. Where possible, use supply planes. Good
connections should be made between the AD7608 supply pins
and the power tracks on the board. Use a single via or multiple
vias for each supply pin.
Good decoupling is also important to lower the supply impedance
Figure 60. Bottom Layer Decoupling
presented to the AD7608 and to reduce the magnitude of the
supply spikes. The decoupling capacitors should be placed close
to (ideally right up against) these pins and their corresponding
ground pins. Place the decoupling capacitors for the REFIN/
REFOUT pin and the REFCAPA and REFCAPB pins as close
as possible to their respective AD7608 pins and where possible
they should be placed on the same side of the board as the AD7608
device. Figure 59 shows the recommended decoupling on the
top layer of the AD7608 board. Figure 60 shows bottom layer
decoupling. Bottom layer decoupling is for the four AV
pins
CC
and the V
pin.
DRIVE
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