SNVAA92 November   2023 LM63625-Q1 , TPS37-Q1 , TPS3703-Q1 , TPS3850-Q1

 

  1.   1
  2.   Abstract
  3. 1Introduction
  4. 2Power Designs for Safety MCUs With Functional Safety Requirements
  5. 3ASIL B Power-Supply Design Example and FMEDA Analysis
    1. 3.1 Functional Safety Requirements
    2. 3.2 Proposed Power Design
    3. 3.3 FMD and Pin FMA
    4. 3.4 LM63625-Q1 and TPS37A-Q1 FMEDA Analysis at the Die Level
    5. 3.5 LM63625-Q1 and TPS37A-Q1 FMEDA Analysis at the Pin Level
      1.      11
    6. 3.6 Total FMEDA Analysis of the LM63625-Q1 and TPS37A-Q1
  6. 4Summary
  7. 5Additional Resources

3.6 Total FMEDA Analysis of the LM63625-Q1 and TPS37A-Q1

Adding the total FIT rate, residual or single-point faults, and latent faults of Table 3-2, Table 3-5, and Table 3-6 produces the overall FIT rate. From there, you can calculate the final SPFM = 99.55% and LFM = 81.74% for this design (Table 3-7), proving that a TI power-supply design with the LM63625-Q1 and TPS37A-Q1 meets ASIL B criteria.

Table 3-7 Total FMEDA Analysis for the LM63625-Q1 and TPS37A-Q1
Die (LM63625) Package (LM63625) Die (TPS37A) Package (TPS37A) Overall
Total FIT λS 7.0000 5.0000 2.0000 3.0000 17.0000
Residual and single point faults λSPF and λRF 0.0420 0.0113 0.0000 0.0000 0.0533
Latent fault λMPF,L 0.0000 0.0000 1.5600 1.5300 3.0900
Single point failure metric SPFM 99.40% 99.77% 100.00% 100.00% 99.69%(1)
Latent failure metric LFM 100.00% 100.00% 22.00% 49.00% 81.77%(2)
(1) SPFM = 1 – 0.0533 / 17 = 99.69%
(2) LFM = 1 – 3.09 / (17-0.0533) = 81.77%