4.1 Automotive Device Mission Profile Example

The values shown in Automotive Device Lifetime Estimates are based on estimates for an always-on device (100% up time). However, all applications are not up 100% of the time and may switch from one operating point (VDD, T_J) to another. Such considerations must be taken into account when estimating lifetime.

To estimate a specific mission profile, use the following tables and examples.

Table 4-2, built from applicable product qualification, temperature and voltage aging acceleration values, lists the A, B, C, D, E and F operating points referred to in the example below.

Table 4-2. Automotive Device Power-on Hours Derating Values
T_J	DR(T_J)	Mission Profile Example
T_J°C < 25°C	937.50	A
30	598.14
35	387.23
40	254.20
45	169.09
50	113.90
55	77.66
60	53.56
65	37.35
70	26.32	B
75	18.73
80	13.46
85	9.76	C
90	7.15
95	5.27
100	3.92	D
105	2.94
110	2.22
115	1.69	E
120	1.30
125	1	F

Table 4-3 summarizes a mission profile example with the following details:

A target lifetime: PoH_{MP_TARGET}
6 operating points (VDD, T_J)
A usage percentage in each operating point

PoH_{MP_TARGET} = 20,000 Hrs

Table 4-3. Automotive Device Mission Profile Example
MP	U%	PoH(T_J, VDD)	T_J °C	V_DD (V)	DR(T_J)	VAF	PoH(125°C, 1.15V)	Comment
A	6	1200	-40	1.15	938	1	1.28	1200 / 938 / 1 = 1.28
B	25	5000	70	1.15	26.3	1	190	5000 / 26.3 / 1 = 190
C	25	5000	85	1.15	9.76	1	512	5000 / 9.76 / 1 = 512
D	25	5000	100	1.15	4	1	1274.4	5000 / 4 / 1 = 1274
E	14	2800	115	1.15	2	1	1655.3	2800 / 2 / 1 = 1655
F	5	1000	125	1.15	1	1	1000	1000 / 1 / 1 = 1000
PoH_MP(125°C, 1.15V) =							4633

The PoH(125°C, 1.15V) column is computed for each line of the mission profile by derating PoH(T_J, VDD) with DR(T_J) and VAF (temperature and voltage derating). Computation results are then summed up into a single value.

If the computed PoH_MP(125°C, 1.15V) is greater than PoH_Q(125°C, 1.15V), then the required PoH_{MP_TARGET} exceeds the device lifetime emulated during the HTOL tests. In such a case, the mission profile must be reviewed.
Conversely, if PoH_MP(125°C, 1.15V) is less than PoH_Q(125°C, 1.15V), as in this example, then the mission profile MP is covered by the HTOL tests.

As explained above, PoH_{MP_TARGET} = 20 kHrs is reached with the example mission profile MP. However, it is interesting to estimate the Power-on Hours with such a mission profile, PoH_{MP_EST}. See the applicable formula in Table 2-1 and its application in the following table.

Table 4-4. Estimated PoH for Example Automotive Device Mission Profile
Result	Value in Hours	Comment
PoH_{MP_EST}	24748	20000 * 5733 / 4633