Datasheet

© 2009 Microchip Technology Inc. DS21881E-page 11
MCP6231/1R/1U/2/4
4.0 APPLICATION INFORMATION
The MCP6231/1R/1U/2/4 family of op amps is
manufactured using Microchip’s state-of-the-art CMOS
process and is specifically designed for low-cost,
low-power and general-purpose applications. The low
supply voltage, low quiescent current and wide
bandwidth makes the MCP6231/1R/1U/2/4 ideal for
battery-powered applications.
4.1 Rail-to-Rail Inputs
4.1.1 PHASE REVERSAL
The MCP6231/1R/1U/2/4 op amp is designed to
prevent phase reversal when the input pins exceed the
supply voltages. Figure 4-1 shows the input voltage
exceeding the supply voltage without any phase
reversal.
FIGURE 4-1: The MCP6231/1R/1U/2/4
Show No Phase Reversal.
4.1.2 INPUT VOLTAGE AND CURRENT
LIMITS
The ESD protection on the inputs can be depicted as
shown in Figure 4-2. 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 4-2: 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
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 4-3
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 4-3: Protecting the Analog
Inputs.
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.
-1.0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
Time (1 ms/div)
Input, Output Voltages (V)
V
OUT
V
IN
V
DD
= 5.0V
G = +2 V/V
Bond
Pad
Bond
Pad
Bond
Pad
V
DD
V
IN
+
V
SS
Input
Stage
Bond
Pad
V
IN
–
V
1
MCP623X
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