MCP6271 datasheet(14/34 Pages) MICROCHIP

14 / 34 page

MCP6271/2/3/4/5

DS21810D-page 14

 2004 Microchip Technology Inc.

4.8.2

LOSSY NON-INVERTING

INTEGRATOR

The non-inverting integrator shown in Figure 4-8 is easy

to build. It saves one op amp over the typical Miller

integrator plus inverting amplifier configuration. The

phase accuracy of this integrator depends on the

matching of the input and feedback resistors, and the

capacitor’s time constants. RF is used to provide

feedback at frequencies << 1/(2

πR

1C1) and makes this

a lossy integrator (it has infinite gain at DC).

FIGURE 4-8:

Non-Inverting Integrator.

4.8.3

CASCADED OP AMP

APPLICATIONS

The MCP6275 provides the flexibility of Low-power

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

MCP6275 eliminates the added cost and space in a

battery-powered application by using two single op

amps with Chip Select (CS) lines or a 10-pin device

with one CS 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 a CS

line becomes suitable. The circuits below show

possible applications for this device.

4.8.3.1

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 resis-

tive loads in the feedback loop (such as an integrator 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 4-9:

Isolating the Load with a

Buffer.

4.8.3.2

Cascaded Gain

Figure 4-10 shows a cascaded gain circuit configura-

tion with Chip Select. Op amps A and B are configured

in a non-inverting amplifier configuration. In this config-

uration, it is important to note that the input offset

voltage of op amp A is amplified by the gain of op amp

A and B, as shown below:

Therefore, it is recommended that you set most of the

gain with op amp A and use op amp B with relatively

small gain (e.g., a unity-gain buffer).

MCP6271

VIN

VOUT

1C1

()C

MCP6275

VOUTB

Load

OUT

INGAGB

OSAGAGB

OSBGB

Where:

GA = op amp A gain

GB = op amp B gain

VOSA = op amp A input offset voltage

VOSB = op amp B input offset voltage

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