60021 datasheet(8/24 Pages) MICROCHIP

8 / 24 page

MCP6001/2/4

DS21733D-page 8

 2003 Microchip Technology Inc.

3.4

Supply Bypass

With this family of operation amplifiers, the power sup-

ply pin (VDD for single supply) should have a local

bypass capacitor (i.e., 0.01 µF to 0.1 µF) within 2 mm

for good high frequency performance. It also needs a

bulk capacitor (i.e., 1 µF or larger) within 100 mm to

provide large, slow currents. This bulk capacitor can be

shared with other parts.

3.5

PCB Surface Leakage

In applications where low input bias current is critical,

PCB (printed circuit board) surface leakage effects

need to be considered. Surface leakage is caused by

humidity, dust or other contamination on the board.

Under low humidity conditions, a typical resistance

between nearby traces is 1012

Ω. A 5V difference would

cause 5 pA, if current-to-flow; this is greater than the

MCP6001/2/4 family’s bias current at 25°C (1 pA, typ).

The easiest way to reduce surface leakage is to use a

guard ring around sensitive pins (or traces). The guard

ring is biased at the same voltage as the sensitive pin.

An example of this type of layout is shown in

Figure 3-4.

FIGURE 3-4:

Example Guard Ring Layout

for Inverting Gain.

Non-inverting Gain and Unity Gain Buffer:

Connect the non-inverting pin (VIN+) to the

input with a wire that does not touch the pcb

surface.

Connect the guard ring to the inverting input

pin (VIN–). This biases the guard ring to the

common mode input voltage.

Inverting and Transimpedance Gain Amplifiers

(convert current to voltage, such as photo detec-

tors):

Connect the guard ring to the non-inverting

input pin (VIN+). This biases the guard ring

to the same reference voltage as the op

amp (e.g., VDD/2 or ground).

Connect the inverting pin (VIN–) to the input

with a wire that does not touch the PCB

surface.

3.6

Application Circuits

3.6.1

UNITY GAIN BUFFER

The rail-to-rail input and output capability of the

MCP6001/2/4 op amp is ideal for unity-gain buffer

applications. The low quiescent current and wide band-

width makes the device suitable for a buffer configura-

tion in an instrumentation amplifier circuit, as shown in

Figure 3-5.

FIGURE 3-5:

Instrumentation Amplifier

with Unity Gain Buffer Inputs.

3.6.2

ACTIVE LOW-PASS FILTER

The MCP6001/2/4 op amp’s low input bias current

makes it possible for the designer to use larger resis-

tors and smaller capacitors for active low-pass filter

applications. However, as the resistance increases, the

noise generated also increases. Parasitic capacitances

and the large value resistors could also modify the fre-

quency response. These trade-offs need to be

considered when selecting circuit elements.

It is possible to have a filter cutoff frequency as high as

1/10th of the op amp bandwidth (100 kHz). Figure 3-6

shows a second-order butterworth filter with 100 kHz

cutoff frequency and a gain of +1V/V.

The

component

values

were

selected

using

Microchip’s FilterLab® software.

FIGURE 3-6:

Active Second-Order Low-

Pass Filter.

Guard Ring

VIN-VIN+

VIN1

MCP6002

VIN2

MCP6002

VREF

MCP6001

VOUT

1/2

VOUT

VIN2 VIN1

–

()

------

•

VREF

R1 = 20 kΩ

R2 = 10 kΩ

14.3 k

Ω

MCP6002

VOUT

53.6 k

Ω

100 pF

VIN

33 pF

60021 数据表(PDF) 8 Page - Microchip Technology

60021 数据表(HTML) 8 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

数据表下载

链接网址

60021 数据表(PDF) 8 Page - Microchip Technology

60021 数据表(HTML) 8 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

数据表 下载

链接网址

数据表下载