MCP6021 View Datasheet(PDF) - Microchip Technology
Part Name
Description
MFG CO.
'MCP6021' PDF : 42 Pages View PDF
4.0 APPLICATIONS INFORMATION
The MCP6021/1R/2/3/4 family of operational amplifiers
are fabricated on Microchip’s state-of-the-art CMOS
process. They are unity-gain stable and suitable for a
wide range of general-purpose applications.
4.1 Rail-to-Rail Input
4.1.1 PHASE REVERSAL
The MCP6021/1R/2/3/4 op amp is designed to prevent
phase reversal when the input pins exceed the supply
voltages. Figure 2-42 shows the input voltage exceed-
ing the supply voltage without any phase reversal.
4.1.2
INPUT VOLTAGE AND CURRENT
LIMITS
The ESD protection on the inputs can be depicted as
shown in Figure 4-1. This structure was chosen to
protect the input transistors, and to minimize input bias
current (IB). The input ESD diodes clamp the inputs
when they try to go more than one diode drop below
VSS. They also clamp any voltages that go too far
above VDD; their breakdown voltage is high enough to
allow normal operation, and low enough to bypass
quick ESD events within the specified limits.
VDD
Bond
Pad
VIN+
Bond
Pad
Input
Stage
Bond
Pad
VIN–
VSS
Bond
Pad
FIGURE 4-1:
Structures.
Simplified Analog Input ESD
In order to prevent damage and/or improper operation
of these op amps, the circuit they are in must limit the
currents and voltages at the VIN+ and VIN– pins (see
Absolute Maximum Ratings † at the beginning of
Section 1.0 “Electrical Characteristics”). Figure 4-2
shows the recommended approach to protecting these
inputs. The internal ESD diodes prevent the input pins
(VIN+ and VIN–) from going too far below ground, and
the resistors R1 and R2 limit the possible current drawn
out of the input pins. Diodes D1 and D2 prevent the
input pins (VIN+ and VIN–) from going too far above
VDD, and dump any currents onto VDD. When
implemented as shown, resistors R1 and R2 also limit
the current through D1 and D2.
MCP6021/1R/2/3/4
VDD
D1 D2
V1
R1
MCP602X
V2
R2
R3
R1
>
VSS
–
(minimum expected
2 mA
V1)
R2
>
VSS
–
(minimum expected
2 mA
V2)
FIGURE 4-2:
Inputs.
Protecting the Analog
It is also possible to connect the diodes to the left of
resistors R1 and R2. In this case, current through the
diodes D1 and D2 needs to be limited by some other
mechanism. The resistors then serve as in-rush current
limiters; the DC current into the input pins (VIN+ and
VIN–) should be very small.
A significant amount of current can flow out of the
inputs when the common mode voltage (VCM) is below
ground (VSS); see Figure 2-42. Applications that are
high impedance may need to limit the useable voltage
range.
4.1.3 NORMAL OPERATION
The input stage of the MCP6021/1R/2/3/4 op amps use
two differential CMOS input stages in parallel. One
operates at low common mode input voltage (VCM),
while the other operates at high VCM. WIth this topol-
ogy, the device operates with Vcm up to 0.3V above
VDD and 0.3V below VSS.
4.2 Rail-to-Rail Output
The Maximum Output Voltage Swing is the maximum
swing possible under a particular output load.
According to the specification table, the output can
reach within 20 mV of either supply rail when
RL = 10 kΩ. See Figure 2-31 and Figure 2-34 for more
information concerning typical performance.
4.3 Capacitive Loads
Driving large capacitive loads can cause stability
problems for voltage feedback op amps. As the load
capacitance increases, the feedback loop’s phase
margin decreases, and the closed loop bandwidth is
reduced. This produces gain-peaking in the frequency
response, with overshoot and ringing in the step
response.
© 2009 Microchip Technology Inc.
DS21685D-page 17
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