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MCP6286

Low Noise, Low Power Op Amp

Microchip Technology 

4.0 APPLICATION INFORMATION

The MCP6286 op amp is manufactured using

Microchip’s state-of-the-art CMOS process and is

specifically designed for low-power, low-noise

applications.

4.1 Input

4.1.1 PHASE REVERSAL

The MCP6286 op amp is designed to prevent phase

reversal when the input pins exceed the supply

voltages. Figure 2-31 shows the input voltage

exceeding 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 (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 goes 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.

VDD

Bond

Pad

VIN+

Bond

Pad

Input

Stage

Bond

Pad

VIN–

VSS

Bond

Pad

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.

MCP6286

VDD

D1 D2

V1

R1

MCP6286

V2

R2

R3

R1

>

VSS

–

(minimum expected

2 mA

V1)

R2

>

VSS

–

(minimum expected

2 mA

V2)

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). (See

Figure 2-33).

4.1.3 NORMAL OPERATION

The input stage of the MCP6286 op amp uses a PMOS

input stage. It operates at low common mode input

voltage (VCM), including ground. With this topology, the

device operates with a VCM up to VDD - 1.2V and 0.3V

below VSS. (See Figure 2-12).The input offset voltage

is measured at VCM = VSS – 0.3V and VDD - 1.2V to

ensure proper operation.

For a unity gain buffer, since VOUT is the same voltage

as the inverting input, VOUT must be maintained below

VDD –1.2V for correct operation.

4.2 Rail-to-Rail Output

The output voltage range of the MCP6286 op amp is

VSS + 15 mV (minimum) and VDD – 15 mV (maximum)

when RL = 10 kΩ is connected to VDD/2 and

VDD = 5.5V. Refer to Figure 2-24 and Figure 2-25 for

more information.

© 2009 Microchip Technology Inc.

DS22196A-page 15

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