Design Project



Homework 11: Reliability and Safety Analysis

Due: Friday, November 9, at NOON

Team Code Name: __wifiMote_________ Group No. ___7___

Team Member Completing This Homework: ____Siddharth Gupta________

e-mail Address of Team Member: ___gupta5___ @ purdue.edu

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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. Introduction

The objective of the wifiMote is to design and create a wireless hand-held television (TV) remote. It will allow a user to “channel surf” without interfering with what is being watched on TV. The remote will have a touch screen Liquid Crystal Display (LCD) interface that will be capable of receiving and displaying a TV video stream. The user will be able to provide inputs through the touch panel interface on the LCD and will be able to change the preview on the handheld and also change the channel on the TV. The device also runs off rechargeable batteries.

The components within the device that can pose reliability issues are the PIC24 microcontroller, LDO voltage regulator, the charge pump and the battery charger. The failure rate and the mean time to failure will be analyzed for each of these components and also possible ways to increase their reliability.

Safety is an important issue as far as consumer products go and the wifiMote being a hand-held device makes the user more prone to any possible hazards. The safety analysis is done by breaking up the device schematic into functional blocks and analyzing the failures for each of these blocks. The blocks to be analyzed are the Microcontroller and LCD, the Charge Pump, the Battery Charger and the Voltage Regulators. The power management system is the most critical part since it has the highest potential to cause harm to the user or to the other components.

2. Reliability Analysis

The components in the design that are most likely to fail will be discussed in details in

this section. Each component has a specific Mean Time To Failure (MTTF) and is dependent on several other parameters. This section will contain reasoning behind choosing each of the parameters. The following components will be analyzed for reliability analysis:

1. NEC UPC2905BT1D 5V LDO Regulator [2]

2. DS2715 Battery Charger [4]

3. LT1947 Charge Pump [5]

4. PIC24HJ256GP210 Microcontroller [3]

The failure rate (λp) and mean time to failure (MTTF) for each component is calculated

using the Military Handbook for Probability Prediction of Electronic Equipment [1]. All the four components fall under the MIL-HDBK-217F microcircuit model. The equation for this model is

(p = (C1*(T + C2*(E)*(Q*(L [1]

where C1 is the microcircuit die complexity failure rate, (T is the temperature factor, C2 is the package failure rate, (E is the environmental factor, (Q is the quality factor and (L is the learning factor. There were certain assumptions made for each of the four components. The first assumption being that the device is operating in a fixed ground environment with temperature and humidity controlled. According to Table 3-2 of the MIL-HDBK-217F[1], this is a ground fixed condition, giving all components a πE value of 2.0. The second assumption is that the wifiMote will have the quality of a commercial product making (Q equal to 10 for all components.

1. NEC UPC2905BT1D 5V LDO Regulator

|Parameter |Value |Explanation |

|C1 |0.02 |Number of Bipolar Transistors is between 100 – 300, Linear device |

|(T |180 |Maximum junction temperature = 150 0C, Bipolar Device [2] |

|C2 |0.0012 |Component is 3 pin, SMT packaging [2] |

|(E |2.0 |Ground Fixed Environment (GF) |

|(Q |10 |Commercial Component |

|(L |1.0 |Part has been in production for more than 2 years [2] |

Table 2.1.1: Different Parameter Values

|(p |36.024 Failures/Million Hours |

|MTTF (1/(p) |27759 Million hours or 3.16 years |

Table 2.1.2: (p and MTTF values

The failure rate of the component is about 36 failures in a million hours which is a high failure rate mainly contributed by the temperature factor. This failure can be of either high or low criticality. It would be a high critical failure if the component gets overheated and burns posing danger to the user. This can be avoided by adding a heat sink on the regulator or a fan to the overall device. The failure of this component could also be less critical, simply halting functionality of the product and causing customer dissatisfaction.

2. DS2715 Battery Charge Controller

|Parameter |Value |Explanation |

|C1 |0.02 |Digital Bipolar Device, Number of gates = 18420/3 = 6140 [6] |

|(T |35 |Maximum junction temperature = 125 0C [4], Bipolar Device, |

| | |Ea = 0.7 ev [6] |

|C2 |0.0072 |Component is 16 pin, Surface Mount [4] |

|(E |2.0 |Ground Fixed Environment (GF) |

|(Q |10 |Commercial Component |

|(L |1.0 |Part has been in production for more than 2 years [7] |

Table 2.2.1: Different Parameter Values

|(p |7.144 Failures/Million Hours |

|MTTF (1/(p) |139977.6 Million hours or 15.98 years |

Table 2.2.2: (p and MTTF values

The failure rate of the Battery Charger is 7.14 failures per million hours. This failure can be of high criticality if the component overcharges the batteries leading to an explosion. This failure rate can be significantly reduced by heat sinking which would reduce the worst case junction temperature (125 0C) of the component.

3. LT1947 Charge Pump

|Parameter |Value |Explanation |

|C1 |0.02 |Number of Bipolar Transistors is between 100 – 300, Linear device |

|(T |58 |Maximum junction temperature = 125 0C [5], Ea = 1 ev [8] |

|C2 |0.0043 |Component is 10 pin, Surface Mount [5] |

|(E |2.0 |Ground Fixed Environment (GF) |

|(Q |10 |Commercial Component |

|(L |1.0 |Part has been in production for more than 2 years [9] |

Table 2.3.1: Different Parameter Values

|(p |11.686 Failures/Million Hours |

|MTTF (1/(p) |85572.4 Million hours or 9.77 years |

Table 2.3.2: (p and MTTF values

The failure rate of the Charge Pump is 11.69 failures per million hours. The failure of this component is of low or medium criticality since it can only cause the LCD to malfunction. This failure can be significantly reduced by heat sinking which would reduce the worst case junction temperature (125 0C) of the component.

4. PIC24HJ256GP210 Microcontroller

|Parameter |Value |Explanation |

|C1 |0.28 |16-bit Microcontroller, Assumed MOS Microcontroller |

|(T |3.1 |Maximum junction temperature = 125 0C, Digital MOS [3] |

|C2 |0.052 |Component is 100 pin [3], Surface Mount, C2 = 3.6*10-4(100)1.08 [1] |

|(E |2.0 |Ground Fixed Environment (GF) |

|(Q |10 |Commercial Component |

|(L |1.0 |Part has been in production for more than 2 years [10] |

Table 2.4.1: Different Parameter Values

|(p |9.72 Failures/Million Hours |

|MTTF (1/(p) |102880.6 Million hours or 11.74 years |

Table 2.4.2: (p and MTTF values

In the above table, the microcontroller is assumed to contain MOS transistors. The failure rate of the microcontroller is 9.72 failures per million hours. This failure is only of low or medium criticality since it can only cause the device to malfunction leading to customer dissatisfaction.

3. Failure Mode, Effects, and Criticality Analysis (FMECA)

In order to study the failure modes, effects and criticality, the entire design was broken up into four main functional blocks. The following were the four major blocks: Microcontroller Unit, Touch Controller and LCD (Block A), Charge pump circuitry for LCD (Block B), Battery Charger circuit (Block C) and Linear voltage regulators for different voltage lines (Block D). The detailed schematics for these four functional blocks can be found in Appendix A of this document. The tables found in Appendix B clearly show the failure modes, effects and criticality of each of these blocks. The possible causes for these failures and methods of detection have also been mentioned in these tables.

The criticality, for the different failures in each block, has been divided into the following categories: High, Medium and Low. A high criticality failure has been defined as any device failure that could be a potential safety concern for the operator. High criticality has a ( ( 10-9. This type of failure may compromise the safety of the operator. A medium failure has been defined as a device failure owing to irreparable damage to the device. Medium criticality has a 10-9 ( ( p( 10-4. A low failure has been defined as a device failure owing to the malfunctioning of some component which can be easily identified and fixed. Low criticality has a ( p > 10-4. Low and Medium failures could cause potential customer dissatisfaction.

During the analysis of the different failure modes, it was assumed that the failure mode was independent and all the other components of the device were functioning correctly. During analysis, each failure was isolated and failures caused because of an existing failure were not considered. It was also assumed that high criticality failures were a result of failures of an active or passive component in the device and not a result of the product design.

4. Summary

This homework studied the major sources of failure for the wifiMOTE. The components analyzed were the PIC24 microcontroller, LDO voltage regulator, charge pump, and battery charger. The overall safety of the device was measured by first measuring the safety of the individual components and then combining those components together to represent the overall final product. The failure rate of the LDO voltage regulator was high, while the failure rate of the other components was at a more acceptable rate. The effects of failure was also analyzed and summarized for the major components. Some critical sources of failure are an overcharged battery leading to LCD damage and a battery charger failure leading to potential rupture of battery and user injury. Were this product to go on to actual production, the sources of critical failure would have to be addressed to ensure that if the device were to fail, it would do so in a way that would not injure the end user.

List of References

1] Department of Defense, “Military Handbook, Reliability Prediction of Electronic Equipment,” [Online], 1991, Available: [Accessed Nov. 8, 2007].

2] NEC Electronics, “UPC2905BT1D-E1-AT”, , [Online]. Available: . [Accessed Nov. 8, 2007].

[3] Microchip Technology, “PIC24HJ256GP210”, , [Online]. Available: . [Accessed Nov. 8, 2007].

[4] Dallas Semiconductor, “DS2715”, maxim-, [Online]. Available:

. [Accessed Nov. 8, 2007].

[5] Linear Technology, “LT1947”, , [Online]. Available:

1061,P1805,D1598 .[Accessed Nov. 8, 2007].

[6] Dallas Semiconductor, “DS2715 Reliability”, maxim-, [Online]. Available:

. [Accessed Nov. 8, 2007].

[7] Dallas Semiconductor, “DS2715 News Release”, maxim-, [Online]. Available:

. [Accessed Nov. 8, 2007].

[8] Linear Technology, “LT1947 Reliability”, , [Online]. Available:

. [Accessed Nov. 8, 2007].

[9] Linear Technology, “LT1947 News Release”, , [Online]. Available:

. [Accessed Nov. 8, 2007].

[10] Microchip Technology, “PIC24HJ256GP210 News Release”, , [Online]. Available: . [Accessed Nov. 8, 2007].

Appendix A: Schematic Functional Blocks

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Figure 2: Charge Pump Circuitry (Block B)

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Figure 3: Battery Charger (Block C)

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Figure 4: Linear voltage regulators for different voltage lines (Block D)

Appendix B: FEMCA Worksheet

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

|A1 |Touch panel controller |Improper voltage supply, damaged |No user taps not detected |Observation |Medium |User cannot change channel on TV or |

| |outputs nothing or garbage |IC (ADS7843), buggy software | | | |set top box |

|A2 |LCD doesn’t power up |Input voltage not correct, LCD |Nothing shows up on LCD |Observation |Medium |Nothing can be viewed on the LCD |

| | |damaged. | | | | |

|A3 |LCD failure (no image or |Software buggy, damaged LCD, |LCD displays random or no |Observation |Low | |

| |random image) |incorrect connection between LCD |image | | | |

| | |and PIC24 | | | | |

|A4 |Battery Output voltage too |Current limiting resistor doesn’t |LCD backlight too bright |Observation |High |LCD Screen can become hot to touch, |

| |high |work |Possible damage | | |lead to possible injury |

| | |Battery unregulated output higher | | | | |

| | |than expected | | | | |

|A5 |PIC24 failure |Buggy Software, bypass capacitors |Can lead to unpredictable |Observation |Medium |PIC24 failure causes most components |

| | |shorted making the PIC24 operate |behavior | | |to fail |

| | |under 3.3 V, damaged IC | | | | |

Table B.1: Microcontroller and LCD (Block A) FMECA

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

|B1 |Input voltage > 3.3 V |Bypass capacitors shorted, damaged|Can damage LT1947or damage |Observation/ Measurement of |Medium |LCD may not work |

| | |IC |the LCD with higher voltage |Voltage | | |

| | | |outputs | | | |

|B2 |Output Voltages are not 15V, |Bypass capacitors shorted, damaged|Can damage the LCD |Observation/ Measurement of |Medium |LCD may not work |

| |-10V and 7.5V |IC (LT1947) | |Voltage | | |

Table B.2: Charge Pump Circuitry (Block B) FMECA

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

|C1 |Battery Charger Failure |Out of tolerance supply voltage, |Batteries do not recharge or |Observation/ |High |Leaking or exploding batteries can |

| | |damaged IC, thermistor damaged |overcharge. Possible battery|Battery status monitor | |lead to user injury. |

| | | |leakage/explosion. |reading. | | |

|C2 |No output voltage from |Dead Batteries |Device inoperable |Observation |Low | |

| |batteries | | | | | |

|C3 |Output voltage from batteries|Improper batteries, |Can lead to damage of other |Observation |Medium |Can damage most of the major |

| |too high |Battery Charger overcharging |components. | | |components on the circuit. |

| | |batteries | | | | |

Table B.3: Battery Charger (Block C) FMECA

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

|D1 |Input voltage (TPS77633) > |Improper batteries, |Can lead to damage of IC |Observation/ Measurement of |Low |IC might have to be replaced |

| |7.2 V |Battery Charger overcharging | |Voltage | | |

| | |batteries | | | | |

|D2 |Short Circuit between power |Bypass capacitors shorted |Damage to the PCB |Observation |Medium- High |Irreparable damage to the components |

| |and ground | | | | |on the PCB, can cause harm to the |

| | | | | | |user |

Table B.4: Linear voltage regulators for different voltage lines (Block D) FMECA

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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.

Figure 1: Microcontroller and LCD (Block A)

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