2.2 Power-on Hours (POHQ(TJ, VDD)) Derating Chart

The following chart shows the estimated PoH for different junction temperatures and different VDDCORE values.

Figure 2-1. SAM9X75 Power-on Hours vs VDDCORE and Derating Chart
Note: The above graph shows estimated lifetimes vs the device junction temperature (TJ). TJ can be characterized in application from the top case temperature (TCASE) measurement using either an infrared camera or a thermocouple sensor glued on the device case. The temperature difference (TJ vs TCASE) is negligible as ΨJ-top (junction-to-package-top characterization parameter) is about 0.5°C/W (in JEDEC conditions) with the device consuming much less than 1W.

Prior to any measurement, for first order calculations, TJ can also be estimated from the device thermal resistance (RJA) and on-die power dissipation. See the following two use cases.

Case 1 (Example for SAM9X7x-I):

- TA = 85°C

- RJA = 38°C/W as specified for JEDEC conditions in the device data sheet

- PD = 450 mW

Result: TJ = TA + RJA x PD = 85 + 38 x 0.45 = 102°C

Case 2 (Example for SAM9X7x-V):

- TA = 105°C

- RJA = 33°C/W as specified for JEDEC conditions in the device data sheet

- PD = 600 mW

Result: TJ = TA + RJA x PD = 105 + 33 x 0.6 = 124.8°C