MCP6044T-ESLASHST datasheet(12/40 Pages) MICROCHIP

12 / 40 page

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 (IB). The input ESD diodes clamp the inputs

when they try to go more than one diode drop below

VSS. They also clamp any voltages that go too far

above VDD; 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 (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, and

dump any currents onto VDD. When implemented as

shown, resistors R1 and R2 also limit the current

through D1 and D2.

FIGURE 4-2:

Protecting the Analog

Inputs.

It is also possible to connect the diodes to the left of the

resistor 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 current into the input pins (VIN+ and

VIN–) should be very small.

A significant amount of current can flow out of the

inputs (through the ESD diodes) when the common

mode voltage (VCM) is below ground (VSS); 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 (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.

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 (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

VDD

VIN+

VSS

Input

Stage

Bond

Pad

VIN–

MCP604X

VDD

R1 >

VSS – (minimum expected V1)

2mA

VOUT

R2 >

VSS – (minimum expected V2)

2mA

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