MCP6031/2/3/4
4.0
APPLICATION INFORMATION
VDD
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.
D1 D2
R1
V1
V2
4.1
Rail-to-Rail Input
MCP603X
4.1.1
PHASE REVERASAL
R2
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.
R3
VSS – (minimum expected V1)
R1 >
R2 >
2 mA
VSS – (minimum expected V2)
2 mA
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 voltage that go too far above
VDD; their breakdown voltage is high enough to allow
normal operation and low enough to bypass ESD
events within the specified limits.
FIGURE 4-2:
Inputs.
Protecting the Analog
It is also possible to connect the diodes to the left of the
resistors R1 and R2. In this case, the currents through
the diodes D1 and D2 need to be limited by some other
mechanism. The resistors then serve as in-rush current
limiters; the DC currents 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).
Bond
VDD
Pad
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 (VCM), while the
other operates at a high VCM. With this topology, the
device operates with a VCM up to 300 mV above VDD
and 300 mV below VSS. The input offset voltage is
measured at VCM = VSS – 0.3V and VDD + 0.3V to
ensure proper operation.
Bond
Pad
Bond
Pad
Input
Stage
VIN+
VIN–
Bond
Pad
VSS
There are two transitions in input behavior as VCM is
changed. The first occurs, when VCM is near
VSS + 0.4V, and the second occurs when VCM is near
VDD – 0.5V. For the best distortion performance with
non-inverting gains, avoid these regions of operation.
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
voltages and currents 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
.
When implemented as shown, resistors R1 and R2 also
limit the current through D1 and D2.
DS22041B-page 14
© 2008 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
