1、Lessons Learned Entry: 0296Lesson Info:a71 Lesson Number: 0296a71 Lesson Date: 1993-08-04a71 Submitting Organization: JPLa71 Submitted by: L. L. Gresham / J. O. BlosiuSubject: Glitches on the Discrete Command Outputs of the Remote Interface Unit (RIU) due to Inherent Integrated Circuit Race Conditio
2、n Abstract: RIU glitches that resulted from a known design problem were benign for Voyager, but posed a serious problem for Topex due to its requirement for faster circuit response. When the glitches occurred during Topex assembly level acceptance test, costly modifications were necessary. Electroni
3、c parts should be utilized only as per manufacturers recommendations. Fully consider new assumptions, performance requirements, and potential risks when adopting an inherited design or inherited test plans.Description of Driving Event: At assembly level acceptance test, 90% of the Topex RIUs used on
4、 the discrete command channels experienced malfunctions (glitches). This problem resulted from the decision to do strobing of the power VCC on/off line rather than using a designated strobe line. This type of unconventional strobing generated a voltage race problem, which translated into an unequal
5、voltage propagation delay internal to the chip, thus causing chip malfunctioning. This design decision dates back to the Voyager project. The RIU glitch phenomena occurred in Voyager, but was considered benign due to slower circuit response required by Voyager. On Topex, resolving the glitch problem
6、 required A) screening and assigning of sixteen RIUs to locations less affected by glitches, and B) inserting RC filters on the central unit harness connector to eliminate glitches in spacecraft commands from the central processor.The described costly Topex modifications were necessary to reduce the
7、 risk associated with the misuse of this part.Additional Keyword(s): PoseidonProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Reference(s): PFR #C04068Lesson(s) Learned: 1. Misuse of electronic parts can cause unexpected chip output response with seri
8、ous mission impact. RIUs are frequently utilized in executing critical subsystem spacecraft function.2. Use of “inherited“ designs does not preclude the need to perform in-depth analyses of all elements.Recommendation(s): 1. Electronic parts should be utilized only as per manufacturers recommendatio
9、ns.2. Cognizant design engineers must consider fully the difference between the current and prior assumptions, electrical performance required, and potential risks when adopting an inherited design.3. Extreme care should be taken when applying any inherited designs since they do not ensure reliabili
10、ty. Similar care should be exercised when implementing inherited test plans.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Parts Materials & ProcessesAdditional Info: Provided by IHSNot for ResaleNo reproducti
11、on or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 1993-03-25a71 Approval Name: Carol Dumaina71 Approval Organization: 125-204a71 Approval Phone Number: 818-354-8242Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
