MCP6021 datasheet(16/34 Pages) MICROCHIP

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MCP6021/1R/2/3/4

DS21685C-page 16

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. Separating

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 the guard

trace 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.

4.11

Typical Applications

4.11.1

A/D CONVERTER DRIVER AND

ANTI-ALIASING FILTER

Figure 4-11 shows a third-order Butterworth filter that

can be used as an A/D converter driver. It has a band-

width of 20 kHz and a reasonable step response. It will

work well for conversion rates of 80 ksps and greater (it

has 29 dB attenuation at 60 kHz).

FIGURE 4-11:

A/D converter driver and

anti-aliasing filter with a 20 kHz cutoff frequency.

This filter can easily be adjusted to another bandwidth

by multiplying all capacitors by the same factor.

Alternatively, the resistors can all be scaled by another

common factor to adjust the bandwidth.

4.11.2

OPTICAL DETECTOR AMPLIFIER

Figure 4-12 shows the MCP6021 op amp used as a

transimpedance amplifier in a photo detector circuit.

The photo detector looks like a capacitive current

source, so the 100 k

Ω resistor gains the input signal to

a reasonable level. The 5.6 pF capacitor stabilizes this

circuit and produces a flat frequency response with a

bandwidth of 370 kHz.

FIGURE 4-12:

Transimpedance Amplifier

for an Optical Detector.

14.7 k

Ω 33.2 kΩ

1.0 nF

100 pF

MCP602X

8.45 k

1.2 nF

Photo

Detector

100 pF

5.6 pF

100 k

VDD/2

MCP6021

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