MCP3302-I/ST Microchip Technology, MCP3302-I/ST Datasheet - Page 18

• Manufacturer Part Number: MCP3302-I/ST
• Description: 13-Bit Differential Input, Low Power A/D Converter with SPI Serial Interface
• Manufacturer: Microchip Technology

MCP3302/04
FIGURE 6-9:
used to implement a 2nd order anti-aliasing filter for
the signal being converted by the MCP3302/04.
6.6
When laying out a printed circuit board for use with
analog components, care should be taken to reduce
noise wherever possible. A bypass capacitor from V
to ground should always be used with this device and
should be placed as close as possible to the device pin.
A bypass capacitor value of 0.1 µF is recommended.
Digital and analog traces should be separated as much
as possible on the board and no traces should run
underneath the device or the bypass capacitor. Extra
precautions should be taken to keep traces with high
frequency signals (such as clock lines) as far as possi-
ble from analog traces.
Use of an analog ground plane is recommended in
order to keep the ground potential the same for all
devices on the board. Providing V
devices in a “star” configuration can also reduce noise
by eliminating current return paths and associated
errors. See Figure 6-10. For more information on layout
tips when using the MCP3302/04 or other ADC
devices, refer to AN-688 “Layout Tips for 12-Bit A/D
Converter Applications”.
FIGURE 6-10: V
configuration in order to reduce errors caused by
current return paths.
DS21697A-page 18
V
IN
7.86 k
14.6 k
0.1 µF
Layout Considerations
Device 1
1 µF
2.2 µF
Reference
4.096V
The MCP601 Operational Amplifier is
DD
Device 2
MCP1541
MCP601
+
-
Connection
traces arranged in a ‘Star’
V
DD
C
L
1 µF
Device 3
IN+
IN-
DD
Device 4
MCP330X
V
REF
connections to
V
DD
10 µF
0.1 µF
DD
6.7
The MCP3302/04 devices provide both digital and ana-
log ground connections to provide another means of
noise reduction. As shown in Figure 6-11, the analog
and digital circuitry are 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 sub-
strate which has a resistance of 5 -10 .
If no ground plane is utilized, then both grounds must
be connected to V
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 as shown in
Figure 6-11. Following these steps will reduce the
amount of digital noise from the rest of the board being
coupled into the A/D Converter.
FIGURE 6-11: Separation of Analog and Digital
Ground Pins.
Utilizing the Digital and Analog
Ground Pins
Digital Side
-SPI Interface
-Shift Register
-Control Logic
DGND
Analog Ground Plane
SS
on the board. If a ground plane is
MCP3302/04
V
Substrate
5 - 10
DD
2001 Microchip Technology Inc.
Analog Side
-Sample Cap
-Capacitor Array
-Comparator
AGND
0.1 µF