MCP6021 datasheet(12/28 Pages) MICROCHIP

12 / 28 page

MCP6021/2/3/4

DS21685B-page 12

 2003 Microchip Technology Inc.

3.0

APPLICATIONS INFORMATION

The MCP6021/2/3/4 family of operational amplifiers

are fabricated on Microchip’s state-of-the-art CMOS

process. They are unity-gain stable and suitable for a

wide range of general-purpose applications.

3.1

Rail-to-Rail Input

The MCP6021/2/3/4 amplifier family is designed to not

exhibit phase inversion when the input pins exceed the

supply voltages. Figure 2-27 shows an input voltage

exceeding both supplies with no resulting phase

inversion.

The input stage of the MCP6021/2/3/4 family of devices

uses two differential input stages in parallel; one

operates at low common-mode input voltage (VCM),

while the other operates at high VCM. With this topology,

the device operates with VCM up to 0.3V past either

supply rail (VSS - 0.3V to VDD + 0.3V) at 25°C. The

amplifier input behaves linearly as long as VCM is kept

within the specified VCMR limits. The input offset voltage

is measured at both VCM =VSS - 0.3V and VDD + 0.3V

to ensure proper operation.

Input voltages that exceed the input voltage range

(VCMR) can cause excessive current to flow in or out of

the input pins. Current beyond ±2 mA introduces

possible reliability problems. Thus, applications that

exceed this rating must externally limit the input current

with an input resistor (RIN), as shown in Figure 3-1.

FIGURE 3-1:

RIN limits the current flow

into an input pin.

3.2

Rail-to-Rail Output

The Maximum Output Voltage Swing is the maximum

swing possible under a particular output load.

According to the specification table, the output can

reach within 20 mV of either supply rail when

RL =10kΩ. See Figure 2-31 and Figure 2-34 for more

information concerning typical performance.

3.3

MCP6023 Chip Select (CS)

The MCP6023 is a single amplifier with chip select

(CS). When CS is high, the supply current is less than

10 nA (typ) and travels from the CS pin to VSS, with the

amplifier output being put into a high-impedance state.

When CS is low, the amplifier is enabled. If CS is left

floating, the amplifier will not operate properly.

Figure 1-1 and Figure 2-39 show the output voltage

and supply current response to a CS pulse.

3.4

MCP6021 and MCP6023 Reference

Voltage

The single op amps (MCP6021 and MCP6023) have

an internal mid-supply reference voltage connected to

the VREF pin (see Figure 3-2). The MCP6021 has CS

internally tied to VSS, which always keeps the op amp

on and always provides a mid-supply reference. With

the MCP6023, taking the CS pin high conserves power

by shutting down both the op amp and the VREF

circuitry. Taking the CS pin low turns on the op amp and

VREF circuitry.

FIGURE 3-2:

Simplified internal VREF

circuit (MCP6021 and MCP6023 only).

See Figure 3-3 for a non-inverting gain circuit using the

internal mid-supply reference. The DC-blocking

capacitor (CB) also reduces noise by coupling the op

amp input to the source.

FIGURE 3-3:

Non-inverting gain circuit

using VREF (MCP6021 and MCP6023 only).

VIN

RIN

VOUT

MCP602X

RIN ≥

(Maximum expected VIN) - VDD

2mA

RIN ≥

VSS - (Minimum expected VIN)

2mA

VDD

VSS

VREF

50 k

Ω

50 k

Ω

(CS tied internally to VSS for MCP6021)

VIN

VOUT

VREF

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