AD7942 Analog Devices, AD7942 Datasheet - Page 23

• Manufacturer Part Number: AD7942
• Manufacturer: Analog Devices

Specifications of AD7942

• Resolution (bits): 14bit
• # Chan: 1
• Sample Rate: 250kSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: (Vref) p-p,Uni (Vref)
• Adc Architecture: SAR
• Pkg Type: CSP,SOP

AD7942
APPLICATION HINTS
LAYOUT
Design the PCB that houses the AD7942 so that the analog and
digital sections are separated and confined to certain areas of
the board. The pinout of the AD7942, with all its analog signals
on the left side and all its digital signals on the right side, eases
this task.
Avoid running digital lines under the device because these
couple noise onto the die, unless a ground plane under the
AD7942 is used as a shield. Fast switching signals, such as
CNV or clocks, should never run near analog signal paths.
Avoid crossover of digital and analog signals.
At least one ground plane should be used. It can be common or
split between the digital and analog sections. In the case of being
Figure 42. Layout Example (Top Layer)
split, the ground plane should be joined underneath the AD7942.
The AD7942 voltage reference input, REF, has a dynamic input
impedance and should be decoupled with minimal parasitic
inductances. This is accomplished by placing the reference
decoupling ceramic capacitor close to, and ideally right up
against, the REF and GND pins. Connect these pins with wide,
low impedance traces.
Finally, decouple the power supply of the AD7942, VDD and
VIO, with ceramic capacitors, typically 100 nF, placed close to
the AD7942. Connect the capacitors using short and large
traces to provide low impedance paths and to reduce the effect
of glitches on the power supply lines. An example of layout
following these rules is shown in Figure 42 and Figure 43.
EVALUATING THE PERFORMANCE OF AD7942
Figure 43. Layout Example (Bottom Layer)
Other recommended layouts for the AD7942 are outlined in
the evaluation board for the AD7942 (EVAL-AD7942CBZ). 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 BRD3.
Rev. B | Page 23 of 24