
ICS8430S07AKI REVISION A SEPTEMBER 3, 2009
20
2009 Integrated Device Technology, Inc.
ICS8430S07I Data Sheet
CLOCK GENERATOR FOR CAVIUM PROCESSORS
2. Junction Temperature.
Junction temperature, Tj, is the temperature at the junction of the bond wire and bond pad directly affects the reliability of the device. The
maximum recommended junction temperature for HiPerClockS devices is 125°C. Limiting the internal transistor junction temperature, Tj, to
125°C ensures that the bond wire and bond pad temperature remains below 125°C.
The equation for Tj is as follows: Tj =
θ
JA * Pd_total + TA
Tj = Junction Temperature
θ
JA = Junction-to-Ambient Thermal Resistance
Pd_total = Total Device Power Dissipation (example calculation is in section 1 above)
TA = Ambient Temperature
In order to calculate junction temperature, the appropriate junction-to-ambient thermal resistance
θ
JA must be used. Assuming no air flow and
a multi-layer board, the appropriate value is 39.5°C/W per Table 7 below.
Therefore, Tj for an ambient temperature of 85°C with all outputs switching is:
85°C + 0.868W * 39.5°C/W = 119.2°C. This is below the limit of 125°C.
This calculation is only an example. Tj will obviously vary depending on the number of loaded outputs, supply voltage, air flow and the type of
board.
Table 7. Thermal Resistance θJA for 32 Lead VFQFN, Forced Convection
θ
JA Vs. Air Flow
Meters per Second
01
2.5
Multi-Layer PCB, JEDEC Standard Test Boards
39.5°C/W
34.5°C/W
31.0°C/W