AD7691 Analog Devices, AD7691 Datasheet - Page 24

• Manufacturer Part Number: AD7691
• Manufacturer: Analog Devices

Specifications of AD7691

• Resolution (bits): 18bit
• # Chan: 1
• Sample Rate: 250kSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: (2Vref) p-p
• Adc Architecture: SAR
• Pkg Type: CSP,SOP

AD7691
APPLICATION HINTS
LAYOUT
The printed circuit board that houses the AD7691 should be
designed so that the analog and digital sections are separated
and confined to certain areas of the board. The pin
configuration of the AD7691, with its analog signals on the left
side and its digital signals on the right side, eases this task.
Avoid running digital lines under the device because this couples
noise onto the die unless a ground plane under the AD7691 is
used as a shield. Fast switching signals, such as CNV or clocks,
should not run near analog signal paths. Crossover of digital
and analog signals should be avoided.
At least one ground plane should be used. It can be common or
split between the digital and analog sections. In the latter case,
the planes should be joined underneath the AD7691.
Figure 47. Example Layout of the AD7691 (Top Layer)
The AD7691 voltage reference input, REF, has a dynamic input
impedance and should be decoupled with minimal parasitic
inductances. This is done by placing the reference decoupling
ceramic capacitor close to, ideally right up against, the REF and
GND pins and connecting them with wide, low impedance traces.
Finally, the power supplies, VDD and VIO, of the AD7691
should be decoupled with ceramic capacitors, typically 100 nF,
placed close to the AD7691 and connected using short, wide
traces to provide low impedance paths and to reduce the effect
of glitches on the power supply lines.
An example layout following these rules is shown in Figure 47
and Figure 48.
EVALUATING THE AD7691 PERFORMANCE
Other recommended layouts for the AD7691 are outlined
Figure 48. Example Layout of the AD7691 (Bottom Layer)
in the documentation of the evaluation board for the AD7691
(EVAL-AD7691CBZ). The evaluation board package includes
a fully assembled and tested evaluation board, documentation,
and software for controlling the board from a PC via the
EVAL-CONTROL BRD3Z.
Rev. B | Page 24 of 28