- Chuck Battikha - Mentor, A Siemens Business
- Doug Smith - Mentor, A Siemens Business
Automotive designs require functional safety analysis, typically accomplished using Failure Modes, Effects and Diagnostic Analysis (FMEDA).
FMEDAs are used to determine each safety goal’s diagnostic coverage, which in turn determines if the design will meet the targeted ASIL requirements. However, if you have ever written an FMEDA, you know how tedious a task this can be. In this paper, we share a push-button solution for creating and automating the FMEDA process.
Analyzing Failure Modes
The ISO 26262 standard  requires quantitative analysis of safety related automotive IC designs. This analysis is used to generate the key functional safety metrics: PMHF1, SPFM2, and LFM3. The standard provides targets for each of these metrics based on the ASIL⁴ requirements of the top-level system that automotive manufacturers expect the IC design to meet. In the case of PMHF, automotive manufacturers will allocate a portion of their system PMHF to your design. Determining these metrics is accomplished by looking at ways the design can fail and result in a hazard—a source of potential harm or malfunctioning behavior⁵. The standard and industry practice is to analyze the failure modes using a table where each design component is broken out and the effects of the failure is quantified in terms of failure rates or FIT⁶. This table is referred to as a Failure Modes, Effects and Diagnostic Analysis, or FMEDA.
The FMEDA lists each component and the percentage each failure mode contributes to the overall FIT rate. By including safety mechanisms in your design, you can mitigate the effect of the failure modes and reduce their contribution to the FIT rate. Each failure mode needs to be evaluated according to the following criteria: is it safety related, what percentage of the design is affected by the failure mode, is it covered by a safety mechanism, and what percentage of the design is covered by the safety mechanism. Table 1 defines the common terms used in the creation of an FMEDA.
Having this information, the failure mode’s FIT rate, residual/single-point FIT rate, safe FIT rate, multi-point FIT rate, and latent FIT rate can be calculated. For example, an FMEDA spreadsheet might take the form shown in Figure 1.
1 Probability metric for random hardware failures.
2 Single-point fault metric. See Part 5 C.2 of .
3 Latent fault metric. See Part 5 C.3 of .
4 Automotive Safety Integrity Level.
5 Part 1 Clause 3.88 of .
6 Failures In Time: the number of component failures per one billion operating hours.
View & Download:
Read the entire Push-Button FMEDAs for Automotive Safety - Automating a Tedious Task technical paper.