MCP6291 datasheet(15/36 Pages) MICROCHIP

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DS21812E-page 15

MCP6291/1R/2/3/4/5

4.9

Application Circuits

4.9.1

MULTIPLE FEEDBACK LOW-PASS

FILTER

The MCP6291/1R/2/3/4/5 op amp can be used in

active-filter applications. Figure 4-8 shows an inverting,

third-order, multiple feedback low-pass filter that can be

used as an anti-aliasing filter.

FIGURE 4-8:

Multiple Feedback Low-

Pass Filter.

This filter, and others, can be designed using

Microchip’s Filter design software. Refer to

Section 5.0

“Design Aids”

4.9.2

PHOTODIODE AMPLIFIER

Figure 4-9 shows a photodiode biased in the photovol-

taic mode for high precision. The resistor R converts

the diode current ID to the voltage VOUT. The capacitor

is used to limit the bandwidth or to stabilize the circuit

against the diode’s capacitance (it is not always

needed).

FIGURE 4-9:

Photodiode Amplifier.

4.9.3

CASCADED OP AMP

APPLICATIONS

The MCP6295 provides the flexibility of Low-power

mode for dual op amps in an 8-pin package. The

MCP6295 eliminates the added cost and space in

battery-powered applications by using two single op

amps with Chip Select lines or a 10-pin device with one

Chip Select line for both op amps. Since the two op

amps are internally cascaded, this device cannot be

used in circuits that require active or passive elements

between the two op amps. However, there are several

applications where this op amp configuration with

Chip Select line becomes suitable. The circuits below

show possible applications for this device.

4.9.3.1

Load Isolation

With the cascaded op amp configuration, op amp B can

be used to isolate the load from op amp A. In applica-

tions where op amp A is driving capacitive or low

resistance loads in the feedback loop (such as an

integrator circuit or filter circuit), the op amp may not

have sufficient source current to drive the load. In this

case, op amp B can be used as a buffer.

FIGURE 4-10:

Isolating the Load with a

Buffer.

MCP6291

VOUT

VIN

VDD/2

MCP6291

VOUT

VDD/2

light

MCP6295

VOUTB

Load

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