Avago Technologies ACPL-224-500E - Manual (Page 14)

AV02-4387EN 12 Avago Technologies
Calculate the LED Lifetime Performance
in Optocouplers to Predict Reliability
The projected field lifetime for the
LED = AF × stress hours = 184.7 ×
1000 = 184,767 hours (or 21 years).
This is the projected field time of the
LED type “AA” that will degrade to
99.2% CTR. With the AF value calcu-
lated, all data points of stress hours
are able to map to the expected field
lifetime time of the LED.
years operation. Depending on the
system design to expected lifespan
usage, the degradation calculations
give designers more flexibility in
choosing the IF value. They can thus
optimize their system designs to
achieve the best combination reli-
able operating lifetime and power
consumption.
Figure 14a. CTR degradation performance vs field years for AlGaAs (Type 1) LED (operating I
F
=16mA, 50% duty cycle, T
A
=80 °C)
Figure 14b. CTR degradation performance vs field years for AlGaAs (Type 2) LED (operating I
F
=5mA, 100% duty cycle, T
A
=80 °C)
In Figures 14a-c, the performance
degradation in CTR is plotted for
the different LED types over 30 field
years of operation at an ambient
temperature of 80°C. As the graphs
show, the LED types degrade by
no more than 10% (the CTR main-
tains greater than 90% of its initial
value) typically at the end of 30 field
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
110%
CTR Degradation
Field Years
AlGaAs (type 1) LED Performance vs Field Years
0 5 10 15 20 25 30
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
110%
CTR Degradation
Field Years
AlGaAs (type 2) LED Performance vs Field Years
0 5 10 15 20 25 30
Ave
Ave-3Std (worst-case)
Ave
Ave-3Std (worst-case)