MCP3304 Microchip Technology, MCP3304 Datasheet - Page 20

• Manufacturer Part Number: MCP3304
• Description: 13-Bit Differential Input, Low Power A/D Converter with SPI Serial Interface
• Manufacturer: Microchip Technology

MCP3302/04
6.5
Inaccurate conversion results may occur if the signal
source for the A/D converter is not a low impedance
source. Buffering the input will overcome the imped-
ance issue. It is also recommended that an analog filter
be used to eliminate any signals that may be aliased
back into the conversion results. This is illustrated in
Figure 6-9, where an op amp is used to drive the ana-
log input of the MCP3302/04. This amplifier provides a
low impedance source for the converter input and a low
pass filter, which eliminates unwanted high frequency
noise. Values shown are for a 10 Hz Butterworth Low
Pass filter.
Low pass (anti-aliasing) filters can be designed using
Microchip’s interactive FilterLab
will calculate capacitor and resistor values, as well as
determine the number of poles that are required for the
application. For more information on filtering signals,
see Application Note 699 “Anti-Aliasing Analog Filters
for Data Acquisition Systems”.
FIGURE 6-9:
Amplifier is used to implement a 2nd order anti-
aliasing filter for the signal being converted by
the MCP3302/04.
DS21697C-page 20
V
IN
7.86 kΩ
14.6 kΩ
0.1 µF
Buffering/Filtering the Analog
Inputs
1 µF
2.2 µF
Reference
4.096V
MCP1541
MCP601
+
-
The MCP601 Operational
C
L
1 µF
®
IN+
software. FilterLab
IN-
MCP330X
V
REF
V
DD
10 µF
0.1 µF
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 on the board should be sepa-
rated as much as possible, with no traces running
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 lay-
out tips when using the MCP3302/04, or other ADC
devices, refer to Application Note 688, “Layout Tips for
12-Bit A/D Converter Applications”.
FIGURE 6-10:
‘Star’ configuration in order to reduce errors
caused by current return paths.
Device 1
Layout Considerations
Device 2
Connection
V
© 2007 Microchip Technology Inc.
DD
V
DD
traces arranged in a
DD
Device 3
connections to
Device 4
DD