MCP6291 datasheet(17/32 Pages) MICROCHIP

17 / 32 page

DS21812E-page 17

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

4.9.3.6

Second-Order MFB Low-Pass Filter

with an Extra Pole-Zero Pair

Figure 4-15 is a second-order multiple feedback low-

pass filter with Chip Select. Use the FilterLab® software

from Microchip to determine the R and C values for the

op amp A’s second-order filter. Op amp B can be used

to add a pole-zero pair using C3, R6 and R7.

FIGURE 4-15:

Second-Order Multiple

Feedback Low-Pass Filter with an Extra Pole-

Zero Pair.

4.9.3.7

Second-Order Sallen-Key Low-Pass

Filter with an Extra Pole-Zero Pair

Figure 4-16 is a second-order, Sallen-Key low-pass

filter with Chip Select. Use the FilterLab® software from

Microchip to determine the R and C values for the op

amp A’s second-order filter. Op amp B can be used to

add a pole-zero pair using C3, R5 and R6.

FIGURE 4-16:

Second-Order Sallen-Key

Low-Pass Filter with an Extra Pole-Zero Pair and

Chip Select.

4.9.3.8

Capacitorless Second-Order

Low-Pass filter with Chip Select

The low-pass filter shown in Figure 4-17 does not

require external capacitors and uses only three

external resistors; the op amp’s GBWP sets the corner

frequency. R1 and R2 are used to set the circuit gain

and R3 is used to set the Q. To avoid gain peaking in

the frequency response, Q needs to be low (lower

values need to be selected for R3). Note that the

amplifier bandwidth varies greatly over temperature

and process. However, this configuration provides a

low cost solution for applications with high bandwidth

requirements.

FIGURE 4-17:

Capacitorless Second-Order

Low-Pass Filter with Chip Select.

VIN

VOUT

MCP6295

VIN

VOUT

MCP6295

VREF

VIN

VOUT

MCP6295

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