Datasheet

© 2007 Microchip Technology Inc. DS21812E-page 15
MCP6291/1R/2/3/4/5
4.9 Application Circuits
4.9.1 MULTIPLE FEEDBACK LOW-PASS
FILTER
The MCP6291/1R/2/3/4/5 op amp can be used in
active-filter applications. Figure 4-8 shows an inverting,
third-order, multiple feedback low-pass filter that can be
used as an anti-aliasing filter.
FIGURE 4-8: Multiple Feedback Low-
Pass Filter.
This filter, and others, can be designed using
Microchip’s Filter design software. Refer to Section 5.0
“Design Aids”
4.9.2 PHOTODIODE AMPLIFIER
Figure 4-9 shows a photodiode biased in the photovol-
taic mode for high precision. The resistor R converts
the diode current I
D
to the voltage V
OUT
. The capacitor
is used to limit the bandwidth or to stabilize the circuit
against the diode’s capacitance (it is not always
needed).
FIGURE 4-9: Photodiode Amplifier.
4.9.3 CASCADED OP AMP
APPLICATIONS
The MCP6295 provides the flexibility of Low-power
mode for dual op amps in an 8-pin package. The
MCP6295 eliminates the added cost and space in
battery-powered applications by using two single op
amps with Chip Select lines or a 10-pin device with one
Chip Select line for both op amps. Since the two op
amps are internally cascaded, this device cannot be
used in circuits that require active or passive elements
between the two op amps. However, there are several
applications where this op amp configuration with
Chip Select line becomes suitable. The circuits below
show possible applications for this device.
4.9.3.1 Load Isolation
With the cascaded op amp configuration, op amp B can
be used to isolate the load from op amp A. In applica-
tions where op amp A is driving capacitive or low
resistance loads in the feedback loop (such as an
integrator circuit or filter circuit), the op amp may not
have sufficient source current to drive the load. In this
case, op amp B can be used as a buffer.
FIGURE 4-10: Isolating the Load with a
Buffer.
MCP6291
V
OUT
V
IN
V
DD
/2
R
3
C
3
C
1
R
1
R
2
C
4
R
4
MCP6291
V
OUT
I
D
V
DD
/2
R
C
light
A
B
MCP6295
CS
V
OUTB
Load