Microchip Technology MCP651 Input Offset Evaluation Board User guide

MCP651

Input Offset

Evaluation Board

User’s Guide

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code hopping

MCP651 INPUT OFFSET

EVALUATION BOARD

USER’S GUIDE

Table of Contents

Preface ........................................................................................................................... 1

Introduction............................................................................................................ 1

Document Layout .................................................................................................. 1

Conventions Used in this Guide ............................................................................ 2

Recommended Reading........................................................................................ 3

The Microchip Web Site ........................................................................................ 3

Customer Support ................................................................................................. 3

Document Revision History................................................................................... 4

Chapter 1. Product Overview

1.1 Introduction ..................................................................................................... 5

1.2 Kit Contents .................................................................................................... 5

1.3 Intended Use .................................................................................................. 6

1.4 Description ..................................................................................................... 6

Chapter 2. Installation and Operation

2.1 Introduction ................................................................................................... 11

2.2 Required Tools ............................................................................................. 11

2.3 Configuring the Lab Equipment and PCB .................................................... 12

2.4 Operating Conditions .................................................................................... 14

2.5 Converting to Other Parameters .................................................................. 15

2.6 Settling Time, Noise and Sampling Rate ...................................................... 17

Chapter 3. Possible Modifications

3.1 Introduction ................................................................................................... 19

3.2 Range of Parts Supported by MCP651 Input Offset Evaluation Board ........ 19

3.3 Changes to Accommodate Other DUTs ....................................................... 21

Appendix A. Schematics and Layouts

A.1 Introduction .................................................................................................. 25

A.2 Schematic and Layouts ................................................................................ 25

A.3 Board – Schematic ....................................................................................... 26

A.4 Board – Combination of the Top Silk Screen, Top Solder Mask and Top Metal

Layers ..................................................................................................... 27

A.5 Board – Top Silk Screen .............................................................................. 28

A.6 Board – Top Solder Mask and Top Metal Layer .......................................... 29

A.7 Board – Bottom Metal Layer ........................................................................ 30

MCP651 Input Offset Evaluation Board User’s Guide

Appendix B. Bill Of Materials (BOM)

B.1 MCP651 Input Offset Evaluation Board BOM .............................................. 31

B.2 Adaptor Board BOM ..................................................................................... 33

Worldwide Sales and Service .....................................................................................34

MCP651 INPUT OFFSET

EVALUATION BOARD

USER’S GUIDE

Preface

NOTICE TO CUSTOMERS

All documentation becomes dated, and this manual is no exception. Microchip tools and documentation are constantly evolving to meet customer needs, so some actual dialogs and/or tool descriptions may differ from those in this document. Please refer to our web site (www.microchip.com) to obtain the latest documentation available.

Documents are identified with a “DS” number. This number is located on the bottom of each page, in front of the page number. The numbering convention for the DS number is “DSXXXXXA”, where “XXXXX” is the document number and “A” is the revision level of the document.

For the most up-to-date information on development tools, see the MPLAB Select the Help menu, and then Topics to open a list of available on-line help files.

IDE on-line help.

INTRODUCTION

This chapter contains general information that will be useful to know before using the MCP651 Input Offset Evaluation Board. Items discussed in this chapter include:

• Document Layout

• Conventions Used in this Guide

• Recommended Reading

• The Microchip Web Site

• Customer Support

• Document Revision History

DOCUMENT LAYOUT

This document describes how to use the MCP651 Input Offset Evaluation Board. The manual layout is as follows:

• Chapter 1. “Product Overview” - Important information about the MCP651 Input

Offset Evaluation Board.

• Chapter 2. “Installation and Operation” – Covers the initial set-up of the

MCP651 Input Offset Evaluation Board. It lists the required tools, shows how to set up the board and how to connect lab equipment. It then demonstrates how to use this board.

• Chapter 3. “Possible Modifications” – Shows how to modify the board for other

single Microchip op amps in SOIC-8, PDIP-8 and other packages.

• Appendix A. “Schematics and Layouts” – Shows the schematic and board

layouts for the MCP651 Input Offset Evaluation Board.

• Appendix B. “Bill Of Materials (BOM)” – Lists the parts used to populate the

MCP651 Input Offset Evaluation Board. Also lists loose parts shipped with the board in an ESD bag, alternate components and components not populated.

MCP651 Input Offset Evaluation Board User’s Guide

CONVENTIONS USED IN THIS GUIDE

This manual uses the following documentation conventions:

DOCUMENTATION CONVENTIONS

Description Represents Examples

Arial font:

Italic characters Referenced books MPLAB® IDE User’s Guide

Emphasized text ...is the only compiler...

Initial caps A window the Output window

A dialog the Settings dialog A menu selection select Enable Programmer

Quotes A field name in a window or

dialog

Underlined, italic text with right angle bracket

Bold characters A dialog button Click OK

N‘Rnnnn A number in verilog format,

Text in angle brackets < > A key on the keyboard Press <Enter>, <F1>

Courier New font:

Plain Courier New Sample source code #define START

Italic Courier New A variable argument file.o, where file can be

Square brackets [ ] Optional arguments mcc18 [options] file

Curly brackets and pipe character: { | }

Ellipses... Replaces repeated text var_name [,

A menu path File>Save

A tab Click the Power tab

where N is the total number of digits, R is the radix and n is a digit.

Filenames autoexec.bat File paths c:\mcc18\h Keywords _asm, _endasm, static Command-line options -Opa+, -Opa- Bit values 0, 1 Constants 0xFF, ‘A’

Choice of mutually exclusive arguments; an OR selection

Represents code supplied by user

“Save project before build”

4‘b0010, 2‘hF1

any valid filename

[options] errorlevel {0|1}

var_name...] void main (void)

{ ... }

THE MICROCHIP WEB SITE

Microchip provides online support via our web site at www.microchip.com. This web site is used as a means to make files and information easily available to customers. Accessible by using your favorite Internet browser, the web site contains the following information:

• Product Support – Data sheets and errata, application notes and sample

programs, design resources, user’s guides and hardware support documents, latest software releases and archived software

• General Technical Support – Frequently Asked Questions (FAQs), technical

support requests, online discussion groups, Microchip consultant program member listing

• Business of Microchip – Product selector and ordering guides, latest Microchip

press releases, listing of seminars and events, listings of Microchip sales offices, distributors and factory representatives

CUSTOMER SUPPORT

Users of Microchip products can receive assistance through several channels:

• Distributor or Representative

• Local Sales Office

• Field Application Engineer (FAE)

• Technical Support

• Development Systems Information Line Customers should contact their distributor, representative or field application engineer

for support. Local sales offices are also available to help customers. A listing of sales offices and locations is included in the back of this document.

Technical support is available through the web site at: http://support.microchip.com

MCP651 Input Offset Evaluation Board User’s Guide

DOCUMENT REVISION HISTORY

Revision A (May 2009)

• Initial Release of this Document.

Chapter 1. Product Overview

1.1 INTRODUCTION

The MCP651 Input Offset Evaluation Board is described by the following:

• Assembly # : 102-00258-R2

• Order # : MCP651EV-VOS

• Name: MCP651 Input Offset Evaluation Board Items discussed in this chapter include:

• Kit Contents

• Intended Use

• Description

1.2 KIT CONTENTS

• One MCP651 Input Offset Evaluation Board, 102-00258-R2

• Important Information “Read First”

MCP651 INPUT OFFSET

EVALUATION BOARD

USER’S GUIDE

FIGURE 1-1: MCP651 Input Offset Evaluation Board Kit Contents.

MCP651 Input Offset Evaluation Board User’s Guide

DDX

DDIIQ

10Ω()+V

DDI

60 mV+

≈

SSX

SSIIQ

10Ω()– V

SSI

60 mV–

≈

1.3 INTENDED USE

The MCP651 Input Offset Evaluation Board is intended to provide a simple means to measure the MCP651 Input Offset Evaluation Board op amp’s input offset voltage under a variety of operating conditions. The measured input offset voltage (V includes the input offset voltage specified in the data sheet (V power supply voltage (PSRR), common mode voltage (CMRR), output voltage (A input offset voltage drift over temperature (ΔV

The MCP651 Input Offset Evaluation Board works most effectively at room temperature (near 25°C). Measurements at other temperatures should be done in an oven where the air velocity is minimal.

1.4 DESCRIPTION

This section starts with the conversion of DUT bias voltages described in the MCP651 data sheet to the voltages on this board. Then there is a discussion of the circuitry that controls the DUT’s output voltage (V (V

OST

details of this board are given in Appendix A. “Schematics and Layouts” and

Appendix B. “Bill Of Materials (BOM)”.

1.4.1 Conversion of Bias Voltages

) plus changes due to:

/ΔTA) and 1/f noise.

) and amplifies its total input offset voltage

OUTX

). Finally, other portions of the circuit, and their purpose, are discussed. Complete

OST

)

The MCP651 data sheet describes all of its bias voltages relative to VSS, which is assumed to be at ground (0V). On the other hand, the MCP651 Input Offset Evaluation Board sets the DUT’s input common mode voltage to 0V. The user needs to convert from the first set of voltages to the second set (by subtracting V

TABLE 1-1: CONVERSION OF BIAS VOLTAGES

Data Sheet Bias Voltage

(V)

OUT

CAL

The supply voltages V quiescent current (I

Conversion Equations

and V

DDX

=6mA):

VCM – V VDD – V

VSS – V

SSX

– V

OUT

VL – V

CAL

– V

can be estimated using the MCP651’s typical

Evaluation Board Bias Voltage

(V)

=0V

CMX

DDI

SSI

OUTX

CALX

EQUATION 1-1:

Product Overview

DUT

OUTX

CMX

=0V

Integrator

1/G

INT

(ω

INT

/s)

DDI

SSI

1/G

INT

+2.5V

-2.5V

+2.5V

-2.5V

COX

+2.5V

-2.5V

Lowpass

Filter

1.4.2 Simplified Circuit and Operation

Figure 1-2 is a simplified diagram of the circuitry that biases the DUT and produces an amplified version of the DUT’s input offset voltage (V a Proportional plus Integral (PI) controller loop, a high gain amplifier and a filter.

). It includes gain at the input,

OST

FIGURE 1-2: Simplified Circuit.

The elements of Figure 1-2 correspond to the components in the complete schematic (A.3 “Board – Schematic”) as follows.

TABLE 1-2: CONVERSION OF SCHEMATIC COMPONENTS

Complete Schematic

Components

R1, R2 R12=R1||R2 ≈ 196.1Ω R3 R3=R3 ≈ 200.0Ω R4 R R5, R6 R R7, R8 R78=R7+R8 ≈ 40.0 kΩ C2 C U1 “DUT” — — U2 “+1 Buffer” — — R11, R12 “1/G R13, R14 = R13 / (R13 + R14) ≈ 1 / (3.213 V/V) U3, R11, R12, C6 “Integrator (ω U3, R17, C7 ω U4, R23, R24, R25, R26, S2 “G

R28, C12 “Lowpass Filter (ω Note 1: Switch S2’s top position is closed when to the right (LOW GAIN), and is open when to the left (HI GAIN).

Simplified Schematic

Component

Conversion

Equations

=R4 ≈ 10.00 kΩ

=R5+R6 ≈ 8.04 kΩ

=C2 ≈ 22 nF

” = R11 / (R11 + R12) ≈ 1 / (3.213 V/V)

INT

/s)” ω

INT

)” ωBW= 1 / (R28 · C12) ≈ 2π (1.59 Hz)

= 1 / ((R11 || R12)C6) ≈ 2π (10.3 Hz)

INT

= 1 / (R17 · C7) ≈ 2π (10.4 Hz)

INT

” =1+R24/R23 ≈ 3.941 V/V, S2 closed

= 1 + (R24 + R25 + R26) / R23 ≈ 39.18V/V, S2open

Typical Values

(Note 1)

MCP651 Input Offset Evaluation Board User’s Guide

OUTXVCOX

≈

VMGAGMV

OST

≈

Where:

GA=1+R4/R3≈ 51.00 V/V

AGM

≈ 201.0 V/V, S2 (position 1) closed ≈ 1998 V/V, S2 (position 1) open

Analysis of this simplified circuit gives the following nominal circuit outputs:

EQUATION 1-2:

and R2 (R12) balance the circuit at the DUT’s input. These resistors are small, and

are oriented on the Printed Circuit Board (PCB) to cancel their thermoelectric voltages. The parallel resistances R DUT’s input bias currents to the measured V affect V V

OST

); the typical value of IOS at +125°C is ±100 pA, which produces a change in

of ±0.02 µV.

The unity gain buffer (+1 gain on the bottom right) isolates the V the following attenuator and integrator. Although it’s not shown here, the resistor R14 at the input to the “+1 Buffer” ensures its output voltage is 0V when the V is left open.

The attenuators (1/G U2 and U3 (“+1 Buffer” and (“Integrator”). For instance, when V V

=0.3V and V

SSI

DDI

1.80V. The differential integrator accumulates the scaled difference between V

, which slowly forces this difference to zero (the I part of the PI controller).

OUTX

Resistor R R

; it minimizes the error at V

injects the integrator’s output at the DUT’s input through resistors R4 and

A proportional term (the P part of the PI controller) is also injected at the DUT’s input through resistor R

negligible above 16 Hz). It also sets a low frequency DUT noise gain of about 505 V/V. This proportional term is rolled off by C interact with the integrator term, and low enough to keep the DUT stable. Thus, C minimizes noise gain at higher frequencies, which reduces the chance of unwanted feedback effects.

With the overall gain G V

values up to either ±12.4 mV or ±1.25 mV. A voltmeter with 1 mV resolution can

OST

distinguish steps of either 5 µV or 0.5 µV, respectively. The DUT’s noise seen at the input to G

and C2 (0.28 kHz). This implies that this noise is dominated by the 1/f noise. The

Lowpass Filter (f

≈ 1.6 Hz) reduces this 1/f noise a little more before it is seen at VM.

The measured noise, over a 140 second period of time with a typical part, was about 19 µV V

referred to input (RTI). This compares favorably with the MCP651’s calibrated

P-P

specification (±200 µV, maximum at +25°C).

||R2 and R3||R4 are equal to minimize the contribution of the

) scale V

INT

and V

COX

(contributions by R5 through R8 do not

OST

input filters from

COX

so that they do not overdrive op amps

OUTX

= 5.6V (given

OUTX

connector

= 5.8V), the voltages at the outputs of the attenuators (1/G

and

COX

OUTX

; it stabilizes the control loop (the integrator term becomes

starting at 0.18 kHz; this is high enough to not

of either 201 V/V or 1998 V/V, this circuit can measure

AGM

has a noise power bandwidth (NPBW) set by

INT

) is

+ 26 hidden pages

Microchip Technology MCP651 Input Offset Evaluation Board User guide

Specifications and Main Features

Frequently Asked Questions

User Manual

Preface

INTRODUCTION

DOCUMENT LAYOUT

CONVENTIONS USED IN THIS GUIDE

RECOMMENDED READING

THE MICROCHIP WEB SITE

CUSTOMER SUPPORT

DOCUMENT REVISION HISTORY

Chapter 1. Product Overview

1.1 INTRODUCTION

1.2 KIT CONTENTS

1.3 INTENDED USE

1.4 DESCRIPTION