MCP602-IP Microchip Technology, MCP602-IP Datasheet

MCP602-IP

Manufacturer Part Number

MCP602-IP

Description

2.7V to 5.5V Single Supply CMOS Op Amp

Manufacturer

Microchip Technology

Datasheet

1.MCP602-IP.pdf (6 pages)

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INTRODUCTION

This Application Note originally started as a “cook

book” for a true 12-bit layout. The assumption of this

type of approach is that a reference design could be

provided, which easily could be used for every layout

implementation. But, the notion of this approach is fairly

unrealistic. There are a multitude of successful ways to

layout out systems with 12-bit Analog-to-Digital (A/D)

Converters and each layout is highly dependent on the

number of devices in the circuit, the types of the

devices (digital or analog) and the environment that the

final product will reside in. Given all of these variables,

it could easily be demonstrated that one successful lay-

out that provides twelve noise free bits from an analog

signal may easily fail in another setting.

Because of the complexity of this problem, this Applica-

tion Note will provide basic guidelines, ending with a

review of issues to be aware of. Throughout the appli-

cation note, examples of good layout and bad layout

implementations will be presented. This will be done in

the spirit of discussing concepts and not with the intent

of recommending one layout as the only one to use.

FIGURE 1: This is a pressure sensor application where the differential signal from the sensor is gained by an

instrumentation amplifier and digitized with a 12-bit A/D Converter, MCP3201. The results of the conversion is displayed

on the LCD display.

Pressure Sensor

1999 Microchip Technology Inc.

Author:

O U T

Layout Tips for 12-Bit A/D Converter Application

Bonnie C. Baker

Microchip Technology Inc.

IA+ IA–

IA–

IA+

–

680

2.5V

----- -

-------- -

MCP602

–

2.5V

MCP602

–

GETTING A GOOD START

Imagine that the task at hand is to design a pressure

sensing circuit that will accurately measure the pres-

sure and present the results on an LCD display screen.

Seems easy enough.

The circuit diagram for this system is shown in Figure 1.

The pressure sensor that is chosen for the job is a

piezo resistive sensor that is configured as a four ele-

ment bridge. The particular sensor that is selected

requires voltage excitation. The full swing output of the

sensor is a small (10s of millivolts) differential signal

that most appropriately is gained by an operational

amplifier structure that also converts the differential

output of the sensor to a single ended analog signal. A

12-bit converter is chosen to match the precision of the

pressure sensor. Once the converter digitizes the volt-

age presented at its input, the digital code is sent to a

microcontroller. The job of the microcontroller is to per-

form tasks such as calibration corrections and linear-

ization. Once this is done, the results are sent to the

LCD display.

The final step in the circuit development is to work

through the calibration and linearization issues associ-

ated with the pressure sensor. Once these issues are

settled, the microcontroller firmware is developed. Now

the board is ready to go to layout.

LCD Display

OUT

12-Bit ADC

MCP3201

AN688

DS00688B-page 1

PICmicro

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