Datasheet

© 2006 Microchip Technology Inc. DS21978C-page 45
MCP4011/2/3/4
8.2 Operational Amplifier
Applications
Figure 8-3, Figure 8-4 and Figure 8-5 illustrate typical
amplifier circuits that could replace fixed resistors with
the MCP4011/2/3/4 to achieve digitally-adjustable
analog solutions.
Figure 8-4 shows a circuit that allows a non-inverting
amplifier to have its’ offset and gain to be independently
trimmed. The MCP4011 is used along with resistors R
1
and R
2
to set the offset voltage. The sum of R
1
+ R
2
resistance should be significantly greater (> 100 times)
the resistance value of the MCP4011. This allows each
increment or decrement in the MCP4011 to be a fine
adjustment of the offset voltage. The input voltage of
the op amp (V
IN
) should be centered at the op amps V
w
voltage. The gain is adjusted by the MCP4012. If the
resistance value of the MCP4012 is small compared to
the resistance value of R
3
, then this is a fine adjustment
of the gain. If the resistance value of the MCP4012 is
equal (or large) compared to the resistance value of R
3
,
then this is a course adjustment of the gain. In general,
trim the course adjustments first and then trim the fine
adjustments.
FIGURE 8-3: Trimming Offset and Gain in
an Inverting Amplifier.
FIGURE 8-4: Trimming Offset and Gain in
a Non-Inverting Amplifier.
FIGURE 8-5: Programmable Filter.
Op Amp
V
IN
V
OUT
B
A
W
+
–
MCP4011
R
1
R
2
B
A
V
DD
W
R
3
R
4
MCP4011
MCP6001
Op Amp
V
IN
V
OUT
–
+
R
1
R
2
B
A
V
DD
W
R
3
MCP6291
MCP4011
MCP4012
AW
V
W
V
DD
Op Amp
V
IN
V
OUT
B
A
W
+
–
MCP4011
R
1
R
2
B
A
V
DD
W
MCP4011
R
3
R
4
f
c
1
2
π R
Eq
C ⋅⋅
-----------------------------=
Pot
1
Pot
2
R
Eq
R
1
R
AB
R
WB
–+()R
2
R
WB
+()R
w
+
||
=
Thevenin
Equivalent
MCP6021