design project - college of engineering - purdue … · web viewhomework 11: reliability and safety...

ECE 477 Digital Systems Senior Design Project Fall 2007

Homework 11: Reliability and Safety AnalysisDue: Friday, November 9, at NOON

Team Code Name: Humphrey’s Treasure Chest Group No. 3

Team Member Completing This Homework: Steven Kingsley

e-mail Address of Team Member: skingsle @ purdue.edu

NOTE: This is the third in a series of four “professional component” homework assignments, each of which is to be completed by one team member. The completed homework will count for 20% of the individual component of the team member’s grade. The body of the report should be 3-5 pages, not including this cover page, references, attachments or appendices.

Evaluation:

SCORE DESCRIPTION

10 Excellent – among the best papers submitted for this assignment. Very few corrections needed for version submitted in Final Report.

9 Very good – all requirements aptly met. Minor additions/corrections needed for version submitted in Final Report.

8 Good – all requirements considered and addressed. Several noteworthy additions/corrections needed for version submitted in Final Report.

7 Average – all requirements basically met, but some revisions in content should be made for the version submitted in the Final Report.

6 Marginal – all requirements met at a nominal level. Significant revisions in content should be made for the version submitted in the Final Report.

* Below the passing threshold – major revisions required to meet report requirements at a nominal level. Revise and resubmit.

* Resubmissions are due within one week of the date of return, and will be awarded a score of “6” provided all report requirements have been met at a nominal level.

Comments:Comments from the grader will be inserted here.


1.0 Introduction

The MIDI-Phone is a very useful device that will convert audio signals into streaming

MIDI, virtually converting any instrument into a MIDI instrument. The potential for this

product is astounding, however without careful considerations and analysis, so could the

dangers. For example, the most dangerous aspect of the MIDI-Phone is the voltage

regulators. If these devices were to fail, the entire system may be damaged which may in turn

cause harm to any users. The following report is an in-depth analysis into the reliability and

safety pertaining to the MIDI-Phone.

2.0 Reliability Analysis

The lifespan of any product is limited by the shortest lifespan of any of the integrated

components. The MIDI-Phone consists of a number of components which may be susceptible

to failure. Fortunately, many of the components are fairly reliable discrete components and

simple integrated circuits. Components that operate at the highest temperatures and involve

the greatest complexity will yield the highest failure rates. The DSP, USB Controller, and

voltage regulators of the MIDI-Phone circuit fit the previously described characteristics.

These components will be analyzed to determine the overall reliability of the MIDI-Phone.

A few of the components involved in the design have significantly higher tendencies to

fail than other components. One of these components is the DSP. According to the Military

Handbook, Equation 1 and Equation 2 will be appropriate to model our DSP.

(1)

(2)

The first variable is defined on page 25 in the Military Handbook to be 0.28 due to the

fact that our DSP is a 16 bit MOS microcontroller. The next variable called the

temperature factor is dependent on the junction temperature, TJ, and the effective activation

energy, Ea. The junction temperature may be evaluated by Equation 3.

(3)

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The first value stands for the ambient temperature. In order to approximate a worst

case scenario, this value was taken to be the maximum ambient operating temperature of our

DSP. The next variable was also provided in the DSP datasheet. The power dissipation,

, was found on the Controlling Power Consumption application note provided by

Freescale. In order to compute the worst case scenario, the power consumption value chosen

describes the maximum power consumption when all modules are utilized.

Variable Value105 °C

74 °C/W547.96 mV

146 °C(Table 1)

Based upon this data, was determined to be 146°C. The effective activation energy

was determined by the fact that our DSP applies to the Digital MOS category. was

determined from the chart by using both of these numbers. The next variable is defined

for surface mount technology by Equation 4.

(4)

The value is defined by the number of pins in our DSP and the result is computed in

Table 2.

Variable Value32

11.82 x 10-3

(Table 2)

The next value to determine is the environment factor . Our product is classified as a

mobile ground device and therefore defines to be 4.0. The next variable , called the

learning factor, is determined to be 1.0 since the DSP has been in production for more than 2

years. The last variable is the quality control factor. The value of the quality control

factor will be 10 to represent that of any normal commercial component.

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Variable Value0.285.0

11.82 x 10-3

4.0101.0

14.47MTTF 7.88 yrs

(Table 3)

Compiling all these values together yields the final result of 14.47 failures/106 hours.

Equation 2 yields a mean time to failure (MTTF) of 7.88 years.

Another component prone to failure is the USB controller. The USB controller may also

be modeled by Equation 1. The MOS component operates on a basis of 8 bits and therefore

may be defined as 0.14 as listed in the Military Handbook. The junction temperature

is provided on page11 of the USB Controller datasheet. This value of 150 °C in conjunction

with the effective activation energy relating to Digital MOS circuits yields a value of 5.6.

Similarly to before, Equation 4 will apply to the USB Controller.

Variable Value32

11.82 x 10-3

(Table 4)

The environmental factor and quality control factor are the same as the DSP since

all of our components are commercial components and will be used in the same environment.

However the learning factor equates to 1.5 since the USB Controller was released in

November 2006.

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Variable Value0.145.6

11.82 x 10-3

4.0101.5

12.47MTTF 9.15 yrs

(Table 5)

Computing the derived values yields a final result of 12.47 failures/106 hours. This value

equates to a MTTF of 9.15 years. The results are summarized in the Table 5.

The last component that requires reliability analysis is the two voltage regulators. Due to

the nature of these devices, Equation 1 will yet again provide an adequate model. The value

of equals 0.02 since the component is estimated to contain 101 to 300 transistors. The

junction temperature is listed on page 5 of the datasheet as 125 °C. This value in conjunction

with the corresponding activation energy for a linear component results in a value of 58.

may be calculated from Equation 4 similar to the DSP and USB Controller.

Variable Value8

2.645 x 10-3

(Table 6)

In addition, both the quality factor and environmental factors will not change for the

voltage regulators since the regulators are not separate from the rest of the circuit. The

learning factor is equal to 1 since the product was developed in May 1999 according to the

voltage regulator datasheet.

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Variable Value0.0258

2.645 x 10-3

4.0101.0

11.71MTTF 9.75 yrs

(Table 7)

Compiling the results as before yields a final result of 11.71 Failures/106 hours. The

equivalent mean time to failure (MTTF) is 9.75 years as shown in Table 7.

The most significant failure rate calculated from the above analysis suggests that the DSP

is the most susceptible to failure. However, this data is construed due to the assumptions

made during analysis. Selecting the worst case scenario rather than the actual operating

characteristics will significantly increase the calculated failure rate and correspondingly

decrease the calculated mean time to failure. The actual failure rate is probably closer to that

of the USB Controller and voltage regulators. Unfortunately, the safest course of action is to

assume that the DSP reliability calculations are correct. The greatest contributing factor to

the failure rate is the quality factor. This value cannot be modified and is susceptible to

debate and controversy. The next greatest contributing factor is the temperature factor. This

factor may be greatly improved my adding heat sinks to the voltage regulators, DSP, and

USB Controller. Another modification to eliminate the contribution of the temperature factor

would be to modify the packaging to allow air flow by the installation of vents and a fan.

These modifications would dramatically decrease the contribution of the temperature factor

to the failure rate.

3.0 Failure Mode, Effects, and Criticality Analysis (FMECA)

Safety is a top priority during the design and development of any product. Each aspect

and component of any design must be analyzed in great detail in order to ensure the

implementation of proper safety feature and measures. The level of safety required must be

measured in order to determine more specifically which components require the greatest

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attention. In order to do so, a number of criticality levels must be defined. Analysis of the

MIDI-Phone circuit will consist of three criticality levels, low, medium, and high. Low

criticality implies that the device may operate improperly, but still be able to continue

operation. Medium criticality is defined as the fault that will cause the system to cease

operation in some way, including damaged components. High criticality is reserved for only

the severe cases in which a malfunction in the device may come to harm any potential users.

Any failures that receive the label as high criticality must also possess a failure rate of at

most 10-9. Any other failure rates are acceptable around the 10-6 range.

A number of assumptions were realized when determining the criticality levels and

effects listed in Appendix B. The most significant assumption was that only one component

would fail at a given time. Failure analysis would become significantly more difficult without

this assumption. Another assumption is that users operating the device would not open or

modify the device in any way. This of course, can not be accounted for when dealing with

predicted failures. Lastly, the assumption that the MIDI-Phone device would not be exposed

to any harsh environments and retain in the same environment as any given PC eliminated

the analysis of some involved and complex failures.

4.0 Summary

The contents of this report have critically examined the reliability and safety concerns

involved with the product named MIDI-Phone. The “worst case scenario” average life

expectancy of a given MIDI-Phone is 7.88 years. The actual life expectancy may be closer

to 9 years, but this has yet to be determined. However before the product may be marketed,

a number of safety issues must be addressed. The most important safety issue is to eliminate

or mitigate the chance of failure from the two voltage regulators. Not only will these voltage

regulators cause damage to the entire system, they may even cause harm to any users. A

consistent and safe operation is necessary for any product to be successful.

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List of References

[1] MIL-HDBK-217F, “Military Handbook,” [Online Document], January, 1990 http://cobweb.ecn.purdue.edu/~dsml/ece477/Homework/CommonRefs/Mil-Hdbk-

217F.pdf

[2] Freescale, “56F8014 Datasheet,” [Online Document], January, 2007 http://www.freescale.com/files/dsp/doc/data_sheet/56f8014.pdf

[3] Maxim, “USB Peripheral/Host Controller,” [Online Document], February, 2007 http://datasheets.maxim-ic.com/en/ds/MAX3421E.pdf

[4] Texas Instruments, “Fast Transient Response Linear Regulators,” [Online Document], January, 2004 http://focus.ti.com/lit/ds/symlink/tps76733.pdf

[5] Freescale, “Controlling Power Consumption in 56F8300 and 56F8100 Family Devices,” [Online Document], September, 2005 http://www.freescale.com/files/dsp/doc/app_note/AN1991.pdf

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http://datasheets.maxim-ic.com/en/ds/MAX4060-MAX4062.pdf










ECE 477 Digital Systems Senior Design Project Spring 2006

Appendix A: Schematic Functional Blocks

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FUNCTION BLOCK A

FUNCTION BLOCK C

FUNCTION BLOCK B

FUNCTION BLOCK D


Appendix B: FEMCA Worksheet

Failure No. Failure Mode Possible Causes Failure Effects Method of Detection Criticality Remarks

A1 Vcc = 0 VWall wart/USB cable

disconnected,TPS76733 damaged

The device will not activate Observation Medium System will not

function

A2 Vcc > 3.3 V or 5 V

TPS76733 damaged,Capacitor short (C91,

C94)

The device will cause other

components to fail and eventually the system itself

Observation High

Could cause entire product to fail and poses danger to user

A3 Exposure to maximum rating

Wall wart/ USB cable faulty

Voltage regulators will fail

over timeObservation High

Product will be limited to a

shortened lifetime and poses

danger to user

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B1 No audio output

Microphone fault, Amplifier fault or gain

set too low, Digital Potentiometer open-fault, Filter fault or cutoff set too low

The device will not output any data Observation Low Operation will still

continue

B2Audio input

exceeds expected value

Amplifier fault or gain is set too high, Loud

input by user

Signal will be incorrectly analyzed

Observation Low

The signal will saturate but still remain safely below VCC

B3 Noisy signalFilter fault or cutoff set

too high, External interference

Signal will be incorrectly analyzed

Observation Low Operation will still continue

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C1 No power

Voltage regulator fault, bulk or bypass

capacitor fault (C41, C42, C43, C44)

The device will cease operation Observation Medium No damage to

the system

C2 Improper power level Voltage regulator fault The device may

become damaged Observation MediumPotential for

damage if power level is high

C3 Incorrect output Software error, PIN damage or ESD

MIDI conversion will be incorrect or

non-existentObservation Medium

ESD and pin damage may

damage system

C4System

sporadically resets

Reset switch fault, Voltage regulator fault, Power connector fault

System will restart Observation Medium No damage to system

C5 No output on the LCD

Software error, DSP fault, resistor fault (R17, R75, R76)

System may operate normally Observation (LCD) Low

Other processes will not be impeded

C6 Incorrect output on the LCD

Software error, DSP fault

System may operate normally Observation (LCD) Low

Other processes will not be impeded

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D1No power or

improper power level

Voltage regulator fault, bulk or bypass

capacitor fault (C51, C52),

USB connection fault

The device will cease operation Observation Medium System operation

will cease

D2 Improper power level

Voltage regulator fault, USB connection fault

The USB Controller will

become damagedObservation Medium

Damage will result to the USB

Controller

D3 Transmit error Software error, DSP fault, USB cable fault

MIDI conversion will be incorrect or

non-existentObservation Medium System operation

will cease

D4 Receive errorSoftware error, DSP

fault, USB cable fault, host computer fault

Operation will pause until

expected data is received

Observation Medium System operation will cease

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