MCP661 datasheet(26/68 Pages) MICROCHIP

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MCP660/1/2/3/4/5/9

DS20002194E-page 26

 2009-2014 Microchip Technology Inc.

4.8

Typical Applications

4.8.1

 LINE DRIVER

Figure 4-10 shows the MCP661 driving a 50

 line. The

large output current (e.g., see Figure 2-18) makes it

possible to drive a back-matched line (RM2, the 50

line and the 50

 load at the far end) to more than ±2V

(the load at the far end sees ±1V). It is worth

mentioning that the 50

 line and the 50 load at the far

end together can be modeled as a simple 50

 resistor

to ground.

FIGURE 4-10:

 Line Driver.

The output headroom limits would be VOL = -2.3V and

VOH = +2.3V (see Figure 2-16), leaving some design

room for the ±2V signal. The open-loop gain (AOL)

typically does not decrease significantly with a 100



load (see Figure 2-11). The maximum power dissipated

about

48 mW

(see

Section 4.2.3

“Power

Dissipation”), so the temperature rise (for the

MCP661 in the SOIC-8 package) is under 8°C.

4.8.2

OPTICAL DETECTOR AMPLIFIER

Figure 4-11 shows a transimpedance amplifier, using

the MCP661 op amp, in a photo detector circuit. The

photo detector is a capacitive current source. RF

provides enough gain to produce 10 mV at VOUT. CF

stabilizes the gain and limits the transimpedance

bandwidth to about 1.1 MHz. The parasitic capacitance

of RF (e.g., 0.2 pF for a 0805 SMD) acts in parallel with

CF.

FIGURE 4-11:

Transimpedance Amplifier

for an Optical Detector.

4.8.3

H-BRIDGE DRIVER

Figure 4-12 shows the MCP662 dual op amp used as

an H-bridge driver. The load could be a speaker or a

DC motor.

FIGURE 4-12:

H-Bridge Driver.

This circuit automatically makes the noise gains (GN)

equal, when the gains are set properly, so that the

frequency responses match well (in magnitude and in

phase). Equation 4-7 shows how to calculate RGT and

RGB so that both op amps have the same DC gains;

GDM needs to be selected first.

EQUATION 4-7:

Equation 4-8 gives the resulting common-mode and

differential mode output voltages.

EQUATION 4-8:

301



301



RM1

49.9



RM2

49.9



Line

+2.5V

-2.5V

MCP66X

Photo

Detector

VDD/2

30 pF

100 k



1.5 pF

100 nA

VOUT

MCP661

VIN

VOT

RGB

VOB

VDD/2

RGT

½ MCP662

–

-----------

–

--------------------------

1 V/V





------------1

–

---------------------

------------

---------------------------

-----------

–

DM VIN

-----------

–





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