Datasheet

 2001-2017 Microchip Technology Inc. DS20001685E-page 19
MCP6021/1R/2/3/4
4.6 MCP6021 and MCP6023 Reference
Voltage
The single operational amplifiers (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 4-8). The MCP6021 has CS inter-
nally tied to V
SS
, which always keeps the operational
amplifier on and always provides a mid-supply refer-
ence. With the MCP6023, taking the CS
pin high
conserves power by shutting down both the operational
amplifier and the V
REF
circuitry. Taking the CS pin low
turns on the operational amplifier and V
REF
circuitry.
FIGURE 4-8: Simplified Internal V
REF
Circuit (MCP6021 and MCP6023 only).
See Figure 4-9 for a non-inverting gain circuit using the
internal mid-supply reference. The DC Blocking
Capacitor (C
B
) also reduces noise by coupling the
operational amplifier input to the source.
FIGURE 4-9: 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 4-10. The
capacitor, C
B
, helps reduce power supply noise on the
output.
FIGURE 4-10: 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 Operational Amplifiers
An unused operational amplifier in a quad package
(MCP6024) should be configured as shown in
Figure 4-11. These circuits prevent the output from tog-
gling and causing crosstalk. Circuit A sets the opera-
tional amplifier at its minimum noise gain. The resistor
divider produces any desired reference voltage within
the output voltage range of the operational amplifier.
The operational amplifier buffers that reference
voltage. Circuit B uses the minimum number of compo-
nents and operates as a comparator, but it may draw
more current.
FIGURE 4-11: Unused Operational
Amplifiers.
V
DD
V
SS
V
REF
CS
50 k
50 k
(CS
tied internally to V
SS
for MCP6021)
5M
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
+
--------------------+=