MCP3301T MICROCHIP [Microchip Technology], MCP3301T Datasheet - Page 19

• Manufacturer Part Number: MCP3301T
• Description: 13-Bit Differential Input, Low Power A/D Converter with SPI Serial Interface
• Manufacturer: MICROCHIP [Microchip Technology]

Using an external operational amplifier on the input
allows for gain and buffers the input signal from the
input to the ADC, allowing for a higher source
impedance. This circuit is shown in
FIGURE 5-5:
for gain and also buffers the input from any high
impedance sources.
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 5-6:
amplifier output swing limitation.
 2011 Microchip Technology Inc.
1 k
1 k
V
V
IN
IN
1 µF
1 µF
REF
10 k
10 k
MCP6022
MCP606
1 M
1 M
+
+
-
-
that is slightly less than the common
1 µF
1 µF
Adding an amplifier allows
Circuit solution to overcome
V
V
IN+
IN-
IN+
IN-
MCP1525
MCP1525
OUT
OUT
V
MCP3301
MCP3301
2.048V
REF
V
V
Figure
0.1 µF
IN
0.1 µF
IN
Figure
V
REF
V
V
DD
DD
0.1 µF
5-5.
0.1 µF
10 k
5-6.
= 5V
= 5V
5.4
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 5-8
common mode voltage. A smaller V
flexibility in a common mode voltage. V
down to 400 mV, exhibit less than 0.1 LSB change in
INL and DNL.
For characterization graphs that show this performance
relationship, see
FIGURE 5-7:
Full Differential input signal versus V
FIGURE 5-8:
versus V
DD
-1
5
4
3
2
1
0
-1
0.25
5
4
3
2
1
0
0.25
+ 0.3V. However, for a given V
Common Mode Input Range
REF
show the relationship between V
1.0
0.5
for Pseudo Differential Input.
Figure 2-2
Common Mode Range of
Common Mode Range
V
V
REF
REF
2.5
1.25
and
4.05V
0.95V
4.05V
0.95V
(V)
MCP3301
(V)
Figure
REF
DS21700D-page 19
REF
Figure 5-7
2-6.
allows for wider
REF
, the common
4.0
2.0
REF
REF
V
.
V
DD
DD
SS
and the
2.8V
2.3V
2.3V
= 5V
levels,
2.8V
= 5V
-0.3V
5.0
2.5
and