MCP3004/3008
6.5
Utilizing the Digital and Analog
Ground Pins
The MCP3004/3008 devices provide both digital and
analog ground connections to provide additional
means of noise reduction. As is shown in Figure 6-5,
the analog and digital circuitry is separated internal to
the device. This reduces noise from the digital portion
of the device being coupled into the analog portion of
the device. The two grounds are connected internally
through the substrate which has a resistance of 5 -10Ω.
If no ground plane is utilized, both grounds must be
connected to VSS on the board. If a ground plane is
available, both digital and analog ground pins should
be connected to the analog ground plane. If both an
analog and a digital ground plane are available, both
the digital and the analog ground pins should be con-
nected to the analog ground plane. Following these
steps will reduce the amount of digital noise from the
rest of the board being coupled into the A/D converter.
VDD
MCP3004/08
Digital Side
Analog Side
-SPI Interface
-Shift Register
-Control Logic
-Sample Cap
-Capacitor Array
-Comparator
Substrate
5 - 10Ω
DGND
AGND
0.1 µF
Analog Ground Plane
FIGURE 6-5: Separation of Analog and Digital
Ground Pins.
DS21295C-page 20
© 2007 Microchip Technology Inc.
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