MCP6283-E/SL Microchip Technology, MCP6283-E/SL Datasheet - Page 13

• Manufacturer Part Number: MCP6283-E/SL
• Description: 450 uA, 5 MHz Rail-to-Rail Op Amp
• Manufacturer: Microchip Technology

3.8.3
The MCP6285 provides the flexibility of low power
mode for dual op amps in an 8-pin package. The
MCP6285 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 chip
select line for each op amp. The only inherent limitation
to this device is that the two op amps are internally cas-
caded. Therefore, 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.
3.8.3.1
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 resis-
tance loads in the feedback loop (such as an integrater
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 3-10:
Buffer.
3.8.3.2
Figure 3-11 shows a cascaded gain circuit configura-
tion with chip select. Op amps A and B are configured
in a non-inverting amplifier configuration. In this config-
uration, it is important to note that the input offset volt-
age of op amp A is amplified by the gain of op amp A
and B as shown below:
Therefore, it is recommended to set most of the gain
with op amp A and use op amp B with relatively small
gain, or as a unity-gain buffer.
 2004 Microchip Technology Inc.
Where:
V
V
V
OUT
OSA
OSB
G
G
A
B
=
= op amp A gain
= op amp B gain
= op amp A offset voltage
= op amp B offset voltage
CASCADED OP AMPS
APPLICATIONS
A
Load Isolation
Cascaded Gain
V
IN
G
A
MCP6285
G
B
Isolating the Load of a
CS
+
V
OSA
G
A
G
B
B
+
V
OSB
G
V
B
OUTB
FIGURE 3-11:
Configuration.
3.8.3.3
Figure 3-12 shows op amp A configured as a difference
amplifier with chip select. In this configuration, it is
recommended to use well-matched resistors (0.1%) to
increase the common mode rejection ratio (CMRR). Op
amp B can be used to provide additional gain and
isolate the load from the difference amplifier.
FIGURE 3-12:
V
V
IN2
IN1
R
V
4
IN
R
R
R
2
2
1
MCP6281/2/3/4/5
Difference Amplifier
R
A
3
R
A
1
MCP6285
Cascaded Gain Circuit
Difference Amplifier Circuit.
MCP6285
CS
CS
R
R
4
2
DS21811C-page 13
R
R
B
1
B
3
V
V
OUT
OUT