
MCP601/1R/2/3/4
DS21314G-page 12
2007 Microchip Technology Inc.
4.0
APPLICATIONS INFORMATION
The MCP601/1R/2/3/4 family of op amps 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
Inputs
4.1.1
PHASE REVERSAL
The MCP601/1R/2/3/4 op amp is designed to prevent
phase reversal when the input pins exceed the supply
voltages.
Figure 2-34
exceeding the supply voltage without any phase
reversal.
4.1.2
INPUT VOLTAGE AND CURRENT
LIMITS
shown in
Figure 4-1
. This structure was chosen to
protect the input transistors, and to minimize input bias
current (I
B
). The input ESD diodes clamp the inputs
when they try to go more than one diode drop below
V
SS
. They also clamp any voltages that go too far
above V
DD
; their breakdown voltage is high enough to
allow normal operation, and low enough to bypass
quick ESD events within the specified limits.
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 V
IN
+ and V
IN
– 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
(V
IN
+ and V
IN
–) from going too far below ground, and
the resistors R
1
and R
2
limit the possible current drawn
out of the input pins. Diodes D
1
and D
2
prevent the
input pins (V
IN
+ and V
IN
–) from going too far above
V
DD
, and dump any currents onto V
DD
. When
implemented as shown, resistors R
1
and R
2
also limit
the current through D
1
and D
2
.
FIGURE 4-2:
Inputs.
Protecting the Analog
It is also possible to connect the diodes to the left of
resistors R
1
and R
2
. In this case, current through the
diodes D
1
and D
2
needs to be limited by some other
mechanism. The resistors then serve as in-rush current
limiters; the DC current into the input pins (V
IN
+ and
V
IN
–) should be very small.
A significant amount of current can flow out of the
inputs when the common mode voltage (V
CM
) is below
ground (V
SS
); see
Figure 2-34
. Applications that are
high impedance may need to limit the useable voltage
range.
4.1.3
NORMAL OPERATION
The Common Mode Input Voltage Range (V
CMR
)
includes ground in single-supply systems (V
SS
), but
does not include V
DD
. This means that the amplifier
input behaves linearly as long as the Common Mode
Input Voltage (V
CM
) is kept within the specified V
CMR
limits (V
SS
–0.3V to V
DD
–1.2V at +25°C).
Figure 4-3
shows a unity gain buffer. Since V
OUT
is the
same voltage as the inverting input, V
OUT
must be kept
below V
DD
–1.2V for correct operation.
FIGURE 4-3:
Limited V
OUT
Range.
Unity Gain Buffer has a
Bond
Pad
Bond
Pad
Bond
Pad
V
DD
V
IN
+
V
SS
Input
Stage
Bond
Pad
V
IN
–
V
1
MCP60X
R
1
V
DD
D
1
R
1
>V
SS
– (minimum expected V
1
)
2 mA
R
2
>V
SS
– (minimum expected V
2
)
2 mA
V
2
R
2
D
2
R
3
MCP60X
–
V
OUT
+
V
IN