MCP3301-I/P Microchip Technology, MCP3301-I/P Datasheet - Page 17

• Manufacturer Part Number: MCP3301-I/P
• Description: 13-Bit Differential Input, Low Power A/D Converter with SPI Serial Interface
• Manufacturer: Microchip Technology

This circuit shows that some headroom will be lost due
to the amplifier output not being able to swing all the
way to the rail. An example would be for an output
swing of 0V to 5V. This limitation can be overcome by
supplying a V
mode voltage. Using a 2.048V reference for the A/D
converter while biasing the input signal at 2.5V solves
the problem. This circuit is shown in Figure 6-6.
.
FIGURE 6-6:
output swing limitation.
6.4
The common mode input range has no restriction and
is equal to the absolute input voltage range: V
to V
mode voltage has a limited swing, if the entire range of
the A/D converter is to be used. Figure 6-7 and
Figure 6-8 show the relationship between V
common mode voltage. A smaller V
flexibility in a common mode voltage. V
to 400 mV exhibit less than 0.1 LSB change in DNL and
INL. Characterization graphs are provided that show
this performance relationship, see Figure 2-9 and
Figure 2-12.
2001 Microchip Technology Inc.
DD
1 k
V
+0.3V. However, for a given V
IN
Common Mode Range
1 µF
REF
10 k
MCP606
Circuit solution to overcome amplifier
1 M
+
-
that is slightly less than the common
1 µF
V
IN+
IN-
MCP1525
OUT
V
MCP3301
2.048V
REF
V
REF
0.1 µF
IN
REF
REF
allows for wider
, the common
V
DD
0.1 µF
levels down
REF
10 k
= 5V
SS
and the
-0.3V
FIGURE 6-7:
Differential input signal versus V
FIGURE 6-8:
for Pseudo Differential Input.
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 analog
input of the MCP3301. 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™ software. 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 the application note AN699 “Anti-Aliasing Analog
Filters for Data Acquisition Systems.
-1
5
4
3
2
1
0
0.25
-1
5
4
3
2
1
0
0.25
Buffering/Filtering the Analog Inputs
1.0
0.5
Common
Common Mode Range versus V
V
V
REF
REF
2.5
1.25
Mode
(V)
4.05V
0.95V
(V)
4.05V
0.95V
MCP3301
REF
.
Range
DS21700A-page 17
4.0
2.0
V
DD
V
DD
of
= 5V
= 5V
2.8V
2.3V
2.3V
2.8V
5.0
2.5
Full
REF