MCP662-ESLASHMF datasheet(25/42 Pages) MICROCHIP

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DS22194A-page 25

MCP661/2/3/5

4.7

High Speed PCB Layout

These op amps are fast enough that a little extra care

in the PCB (Printed Circuit Board) layout can make a

significant difference in performance. Good PC board

layout

techniques

will

help

you

achieve

the

performance shown in the specifications and Typical

Performance Curves; it will also help you minimize

EMC (Electro-Magnetic Compatibility) issues.

Use a solid ground plane. Connect the bypass local

capacitor(s) to this plane with minimal length traces.

This cuts down inductive and capacitive crosstalk.

Separate digital from analog, low speed from high

speed, and low power from high power. This will reduce

interference.

Keep sensitive traces short and straight. Separate

them from interfering components and traces. This is

especially important for high frequency (low rise time)

signals.

Sometimes, it helps to place guard traces next to victim

traces. They should be on both sides of the victim

trace, and as close as possible. Connect guard traces

to ground plane at both ends, and in the middle for long

traces.

Use coax cables, or low inductance wiring, to route

signal and power to and from the PCB. Mutual and self

inductance of power wires is often a cause of crosstalk

and unusual behavior.

4.8

Typical Applications

4.8.1

Ω LINE DRIVER

Figure 4-10 shows the MCP661 driving a 50

Ω line. The

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

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

line and the 50

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

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

mentioning that the 50

Ω line and the 50Ω load at the far

end together can be modeled as a simple 50

Ω resistor

to ground.

FIGURE 4-10:

Ω 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

about

1.1 MHz.

RF’s parasitic

capacitance (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

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

motor.

FIGURE 4-12:

H-Bridge Driver.

301

RM1

49.9

RM2

49.9

Line

+2.5V

-2.5V

MCP66X

Photo

Detector

VDD/2

30pF

100 k

1.5 pF

100 nA

VOUT

MCP66X

VIN

VOT

RGB

VOB

VDD/2

RGT

½ MCP662

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