Datasheet
© 2009 Microchip Technology Inc. DS21685D-page 19
MCP6021/1R/2/3/4
4.6 MCP6021 and MCP6023 Reference
Voltage
The single op amps (MCP6021 and MCP6023), not in
the SOT-23-5 package, have an internal mid-supply
reference voltage connected to the V
REF
pin (see
Figure 4-7). The MCP6021 has CS internally tied to
V
SS
, which always keeps the op amp on and always
provides a mid-supply reference. With the MCP6023,
taking the CS pin high conserves power by shutting
down both the op amp and the V
REF
circuitry. Taking
the CS pin low turns on the op amp and V
REF
circuitry.
FIGURE 4-7: Simplified internal V
REF
circuit (MCP6021 and MCP6023 only).
See Figure 4-8 for a non-inverting gain circuit using the
internal mid-supply reference. The DC-blocking
capacitor (C
B
) also reduces noise by coupling the op
amp input to the source.
FIGURE 4-8: Non-inverting gain circuit
using V
REF
(MCP6021 and MCP6023 only).
To use the internal mid-supply reference for an
inverting gain circuit, connect the V
REF
pin to the
non-inverting input, as shown in Figure 4-9. The
capacitor C
B
helps reduce power supply noise on the
output.
FIGURE 4-9: Inverting gain circuit using
V
REF
(MCP6021 and MCP6023 only).
If you don’t need the mid-supply reference, leave the
V
REF
pin open.
4.7 Supply Bypass
With this family of operational amplifiers, the power
supply pin (V
DD
for single supply) should have a local
bypass capacitor (i.e., 0.01 µF to 0.1 µF) within 2 mm
for good, high-frequency performance. It also needs a
bulk capacitor (i.e., 1 µF or larger) within 100 mm to
provide large, slow currents. This bulk capacitor can be
shared with nearby analog parts.
4.8 Unused Op Amps
An unused op amp in a quad package (MCP6024)
should be configured as shown in Figure 4-10. These
circuits prevent the output from toggling and causing
crosstalk. Circuits A sets the op amp at its minimum
noise gain. The resistor divider produces any desired
reference voltage within the output voltage range of the
op amp; the op amp buffers that reference voltage.
Circuit B uses the minimum number of components
and operates as a comparator, but it may draw more
current.
FIGURE 4-10: Unused Op Amps.
V
DD
V
SS
V
REF
CS
50 kΩ
50 kΩ
(CS
tied internally to V
SS
for MCP6021)
5MΩ
V
IN
R
G
R
F
V
OUT
C
B
V
REF
V
IN
R
G
R
F
V
OUT
V
REF
C
B
V
DD
V
DD
¼ MCP6024 (A) ¼ MCP6024 (B)
R
1
R
2
V
DD
V
REF
V
REF
V
DD
R
2
R
1
R
2
+
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