SNAA391 june   2023 LMK6C , LMK6D , LMK6H , LMK6P

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2MTBF and FIT Calculations for BAW Oscillators
  6. 3Using the Online Estimator to Calculate MTBF and FIT
  7. 4Importance of Mission Profiles for FIT Rate Calculations
  8. 5Summary
  9. 6References

4 Importance of Mission Profiles for FIT Rate Calculations

Mission profile is an important method for evaluating FIT rates in more practical use cases. The Calculating FIT for a Mission Profile application note explains how to use de-rating tools provided by TI in more detail.

The FIT rate calculations are worst-cast FIT values assuming one single operating temperature throughout the lifetime of the device. But in reality, the end system or end product where the oscillator is mounted is not experiencing the same higher temperature throughout the full device lifetime. The oscillator typically experiences a variety of temperatures over a period of time. The FIT value can be better than the worst-case value if the exact operating (use) temperatures are known and also the approximate percentage of time the oscillator is experiencing this temperature over the lifetime of the device.

Table 4-1 provides an example mission profile along with the FIT calculations. For speicific applications, creating a similar table to Table 4-1, can help in calculating the FIT rate for a real system. This table values are different for different application use cases.

Table 4-1 De-rated FIT Calculation
Operating or Use Temperature
(°C)		 % Time De-Rated FIT FIT x
(% Time)
20 25 0.1 0.025
30 35 0.2 0.07
60 30 2.2 0.66
85 10 11.9 1.19
Mission Profile FIT rate 1.945

The FIT number is 1.945 for this example use-case. If this example is calculated just at 85 °C operation temperature with 100% time, the FIT number is 11.9, which is much higher than the practical use-case. Hence, understanding the use case of the system and using the MTBF or FIT calculator to find out the FIT number for the actual use-case is crucial.