MCP3304 Microchip Technology, MCP3304 Datasheet - Page 19

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

FIGURE 6-5:
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 6-5.
FIGURE 6-6:
amplifier output swing limitation.
© 2007 Microchip Technology Inc.
1 kΩ
1 kΩ
V
V
IN
IN
1 μF
1 µF
REF
10 kΩ
10 kΩ
MCP6021
MCP606
1 MΩ
1 MΩ
+
+
-
-
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
MCP330X
MCP330X
2.048V
REF
V
V
0.1 µF
IN
0.1 μF
IN
V
REF
V
V
0.1 μF
DD
DD
0.1 µF
10 kΩ
= 5V
= 5V
6.4
The common mode input range has no restriction and is
equal to the absolute input voltage range: V
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 swing. A smaller V
wider flexibility in a common mode voltage. V
down to 400 mv, exhibit less than 0.1 LSB change in
DNL and INL. For characterization graphs that show
this performance relationship, see Figure 2-9 and
Figure 2-12.
FIGURE 6-7:
of Full Differential Input Signal versus V
FIGURE 6-8:
versus V
DD
-1
-1
5
4
3
2
1
0
0.25
+ 0.3V. However, for a given V
5
4
3
2
1
0
0.25
Common Mode Input Range
REF
1.0
0.5
for Pseudo Differential Input.
MCP3302/04
Common Mode Input Range
Common Mode Input Range
V
V
REF
REF
2.5
1.25
4.05V
0.95V
4.05V
(V)
0.95V
(V)
DS21697C-page 19
REF
, the common
REF
4.0
2.0
REF
V
SS
REF
REF
DD
V
allows for
DD
-0.3V to
and the
= 5V
levels,
2.8V
.
= 5V
2.3V
2.3V
2.8V
5.0
2.5