Datasheet

MCP6041/2/3/4
DS21669D-page 12  2001-2013 Microchip Technology Inc.
4.0 APPLICATIONS INFORMATION
The MCP6041/2/3/4 family of op amps is manufactured
using Microchip’s state of the art CMOS process.
These op amps are unity gain stable and suitable for a
wide range of general purpose, low-power applica-
tions.
See Microchip’s related MCP6141/2/3/4 family of op
amps for applications, at a gain of 10 V/V or higher,
needing greater bandwidth.
4.1 Rail-to-Rail Input
4.1.1 PHASE REVERSAL
The MCP6041/2/3/4 op amps are designed to not
exhibit phase inversion when the input pins exceed the
supply voltages. Figure 2-10 shows an input voltage
exceeding both supplies with no phase inversion.
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 (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: Simplified Analog Input ESD
Structures.
In order to prevent damage and/or improper operation
of these amplifiers, the circuit must limit the currents
(and voltages) at the input pins (see Absolute Maxi-
mum Ratings † at the beginning of Section 1.0 “Elec-
trical 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: Protecting the Analog
Inputs.
It is also possible to connect the diodes to the left of the
resistor R
1
and R
2
. In this case, the currents through
the diodes D
1
and D
2
need 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 (through the ESD diodes) when the common
mode voltage (V
CM
) is below ground (V
SS
); see
Figure 2-33. Applications that are high impedance may
need to limit the useable voltage range.
4.1.3 NORMAL OPERATION
The input stage of the MCP6041/2/3/4 op amps uses
two differential input stages in parallel. One operates at
a low common mode input voltage (V
CM
), while the
other operates at a high V
CM
. With this topology, the
device operates with a V
CM
up to 300 mV above V
DD
and 300 mV below V
SS
. The input offset voltage is
measured at V
CM
=V
SS
–0.3V and V
DD
+ 0.3V to
ensure proper operation.
There are two transitions in input behavior as V
CM
is
changed. The first occurs, when V
CM
is near
V
SS
+ 0.4V, and the second occurs when V
CM
is near
V
DD
–0.5V (see Figure 2-3 and Figure 2-6). For the
best distortion performance with non-inverting gains,
avoid these regions of operation.
Bond
Pad
Bond
Pad
Bond
Pad
V
DD
V
IN
+
V
SS
Input
Stage
Bond
Pad
V
IN
–
V
1
MCP604X
R
1
V
DD
D
1
R
1
>
V
SS
– (minimum expected V
1
)
2mA
V
OUT
R
2
>
V
SS
– (minimum expected V
2
)
2mA
V
2
R
2
D
2
R
3