Datasheet

MCP6031/2/3/4
DS22041B-page 14 © 2008 Microchip Technology Inc.
4.0 APPLICATION INFORMATION
The MCP6031/2/3/4 family of op amps is manufactured
using Microchip’s state-of-the-art CMOS process and
is specifically designed for low-power, high precision
applications.
4.1 Rail-to-Rail Input
4.1.1 PHASE REVERASAL
The MCP6031/2/3/4 op amps are designed to prevent
phase reversal when the input pins exceed the supply
voltages. Figure 2-32 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 (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 voltage that go too far above
V
DD
; their breakdown voltage is high enough to allow
normal operation and low enough to bypass 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 op amps, the circuit they are in must limit the
voltages and currents 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
.
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
resistors 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 currents 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
).
4.1.3 NORMAL OPERATION
The input stage of the MCP6031/2/3/4 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. 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
MCP603X
R
1
V
DD
D
1
R
1
>
V
SS
– (minimum expected V
1
)
2mA
R
2
>
V
SS
– (minimum expected V
2
)
2mA
V
2
R
2
D
2
R
3