Homework 11: Reliability and Safety Analysis Due: Friday, April 10, at NOON

Transcription

1 Homework 11: Reliability and Safety Analysis Due: Friday, April 10, at NOON Team Code Name: Digi-iGuide Group No. 11 Team Member Completing This Homework: Felix Tanjono Address of Team Member: 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 body of the report should be 3-5 pages, not including this cover page, references, attachments or appendices. Evaluation: SCORE DESCRIPTION Excellent among the best papers submitted for this assignment. Very few 10 corrections needed for version submitted in Final Report. Very good all requirements aptly met. Minor additions/corrections needed for 9 version submitted in Final Report. Good all requirements considered and addressed. Several noteworthy 8 additions/corrections needed for version submitted in Final Report. Average all requirements basically met, but some revisions in content should 7 be made for the version submitted in the Final Report. Marginal all requirements met at a nominal level. Significant revisions in 6 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: Add some nice text in Section 2. Don t use a list, write it in paragraph form. And tell us not only what it controls but what could happen if it fails. There are also items in your FMECA chart that are marked high but don t seem to be capable of injuring your user. Also, please see comments inserted in the report.

2 1.0 Introduction Our design project is a GPS navigator used in navigating the campus using the shortest-path algorithm. The navigator will be operating on 3.7 V battery and interface the information to the user using a touch screen LCD. The internal circuits are divided into two main parts. The first involves the microprocessor and its respective peripherals. The second is the power circuits. The most critical part between these two is the power circuits since it supplies power to the other parts. Any failure or incorrect operations in any of these parts will render the device useless. 2.0 Reliability Analysis PIC32MX440 The most complicated IC on the board. It interfaces directly with the W25X64 FLASH chips, the GPS via header, and LCD through its header. It operates above room temperature. TPS63030DSKT The buck boost converter responsible for providing the 3.3 volt rail from either the wall wart or battery voltage. This powers the W25X64 FLASH chips, PIC32MX440, and the debugging LED s. It operates above the room temperature. LT volts DC/DC converter. This component is responsible for powering the LCD and GPS. It operates above the room temperature. W25X64 FLASH memory chip for storing table lookup of all the shortest paths. It operates above the room temperature. -1-

3 PIC32MX440 λ p = (C 1 π T + C 2 π E ) π Q π L [1] Parameter name Description Value Comments regarding choice of parameter value, especially if you had to make assumptions. C 1 Die complexity 0.14 For PIC component [2] π T Temperature coeff. 1.5 For PIC component [2] C 2 Package failure rate pins, non-hermetic [1], [3] π E Environmental 4 For mobile ground use [1] constant π Q Quality factor 10 Assuming for commercial component [2] π L Learning factor 1 Assume more then 2 years in production [2] Entire design: Reliability model 3.38 failure/10 6 hours MTTF Mean time to failure hours (33.75 years) W25X64 FLASH λ p = (C 1 π T + C 2 π E + λ cyc ) π Q π L [1] Parameter name Description Value Comments C 1 Die complexity est memory size for flash. λ cyc Read/write cycling induced 0 Assume it is not Flotox or textured-poly EEPROMS [1] π T Temperature coeff Assume MOS [1] C 2 Package failure rate functional pin, nonhermetic. [1], [4] π E Environmental constant 4 Assume mobile, ground use [1] π Q Quality factor 10 Assuming for commercial product [2] -2-

4 π L Learning factor 1 Assume more then 2 years in production [2] Entire design: Reliability model failure/10 6 hours MTTF Mean time to failure hours (619 years) LT1302 λ p = (C 1 π T + C 2 π E ) π Q π L [1] Parameter name Description Value Comments C 1 Die complexity 0.01 Contain 1 to 100 transistors and MOS [1] π T Temperature coeff. 21 Assume mobile, ground application.[1] C 2 Package failure rate Non-hermetic package. [1], [6] π E Environmental constant 4 Assume mobile, ground application [1] π Q Quality factor 10 Assuming for commercial product [2] π L Learning factor 1 Assume more then 2 years in production [2] Entire design: Reliability model failures/10 6 hours MTTF Mean time to failure hours (51 years) TPS63030DSKT λ p = (C 1 π T + C 2 π E ) π Q π L [1] Parameter name Description Value Comments C 1 Die complexity 0.01 Contain 1 to 100 transistors and MOS [1] π T Temperature coeff. 180 At maximum T J = 150 [5] C 2 Package failure rate Non-hermetic package [1], [5] -3-

5 π E Environmental constant 4 Assume mobile, ground application [1] π Q Quality factor 10 Assuming for commercial product [2] π L Learning factor 1.8 Less then a year in production. [1] Entire design: Reliability model failures/10 6 hours MTTF Mean time to failure hours (~3.5 years) The overall analysis of the four components predicts very high reliability, with three of the four components having more then ten years of mean time to failure. The one remaining component (TPS63030DSKT) selected is the exception with only mean time to failure of ~3.5 years. Some assumptions are made in determining some of the variables in the reliability model s equation. A change in these values will definitely change the overall model, making it more realistic and hopefully improves on the reliability of the design. Reliability could also be improved by finding components that have greater MTTF s. 3.0 Failure Mode, Effects, and Criticality Analysis (FMECA) There are 2 criticality levels chosen: low and high criticality. Low criticality failure ranges from minor user annoyance (battery charging takes too long, etc) to shorted parts which underpowered parts of the circuits. Simple replacement of those parts will fix the failure. criticality failure can be defined as serious component failure that leads to cascading breakdown to other connecting circuits, which in turn could lead to major injury to user when they are handling the device. Most of the component s failure happens under the assumption that part of the circuit was accidentally exposed to conductive material accidently such as liquid spills. 4.0 Summary Detailed insight into the reliability of four of the most complex IC in the circuit (PIC32MX440, W25X64, TPS63030DSKT, and LT1302) yield surprisingly high consistency in mean time to -4-

6 failure with the exception of the TPS63030DSKT 3.3 volt buck/boost converter. Replacement with a more dependable part or a change in the assumption when determining values for the failure model equation will raise the mean time to failure of that module. When looking at all functional blocks of the schematics of the design, all of the possible malfunctions can be categorized into low and high criticality depending on the severity of the problems. Most of these could be avoided by steering clear of any conductive media touching any section of the circuit board. -5-

7 List of References [1] Military Handbook Reliability prediction of electronic equipment, MIL-HDBK-217F, Washington DC, 2 January [2] George Novacek. (2000, December). Designing for Reliability, Maintainability, and safety. pp , [3] PIC32MX3XX/4XX Family Data Sheet, Microchip, Chandler, AZ [4] 16 M-BIT, 32 M-BIT, and 64 M-BIT Serial flash memory with 4 KB sectors and dual output SPI, Winbond, 5 May 2008, Revision I. [5] efficiency single inductor buck-boost converter with 1-A switches, Texas Instruments, Dallas, TX, March 2009, [6] Micropower high output current step-up adjustable and fixed 5V DC/DC converters, Linear Technology, Milpitas, CA. -6-

8 Appendix A: Schematic Functional Blocks A B C -7-

9 D -8-

10 E F -9-

11 G -10-

12 H -11-

13 Appendix B: FMECA Worksheet Failure No. A1 Failure Mode Possible Causes Failure Effects Method of Detection BAT pin = 0 Failure on U4, R12 Battery will not charge Criticality Remarks Can be eliminated by replacing the respective parts. A2 BAT pin = high Failure on R12, U4 Battery cannot supply power Can be eliminated by replacing the respective parts. B1 Output = 0 V SW2 is open Device is off Low B2 D10 or D12 fails Cannot switch between charging and providing power to the battery C Output = 0 V U1 fails Unable to monitor battery level Probe using Multimeter. Low Not essential for the entire circuits to be working. Might cause minor annoyance for user, as they cannot see battery level. -12-

14 D1 Output = 0 V F1 is open. F1 shorts and burn the TPS75701KTTT Unable to draw power from wall wart. Only happen when a sudden power surge happen from the wall wart. D2 Output 4.7 V R26 shorted. Will send out unpredictable voltage to the buck/boost circuit. E1 Output > +3.3 V L1 fails and R28 shorted Destroy the flash chips and PIC32 microprocessor. E2 Output < +3.3V (~ 0.5 V) R27 shorted Not enough voltage to power flash chips and PIC32 microprocessor. Probe at the output Low E3 Output oscillate unpredictably Failure at C15 and TPS63030DSKT Destroy the flash chips and PIC32 microprocessor. -13-

15 F1 Output > 5 V Failure at L2, D11, D9, R9 and LT1302 Possible burn to the GPS and LCD module. F2 Output < 5 V (~ 1.2 V) R8 fails Not enough voltage to power GPS and LCD modules. or probe at that part. Low G1 Nothing works Failure at C27, PIC32MX440 PIC32 becomes unstable G2 Wrong output from PIC32. Y1 oscillating incorrectly PIC32 run incorrectly Check the output from the microprocessor Low H Unable to store/receive data to/from flash chips Failure at U2 and U3 Device will not run. Test the output on the SPI pins. Assume all hold-up resistor is intact. -14-