ICS813078I Datasheet, PDF (22/26 Pages) Integrated Device Technology – FEMTOCLOCKS™ VCXO-PLL FREQUENCY GENERATOR FOR WIRELESS INFRASTRUCTURE EQUIPMENT

ICS813078I
FEMTOCLOCKS™ VCXO-PLL FREQUENCY GENERATOR
2. Junction Temperature.
Junction temperature, Tj, is the temperature at the junction of the bond wire and bond pad and directly affects the reliability of the device.
The maximum recommended junction temperature for HiPerClockS devices is 125°C.
The equation for Tj is as follows: Tj = θ_JA * Pd_total + T_A
Tj = Junction Temperature
θ_JA = Junction-to-Ambient Thermal Resistance
Pd_total = Total Device Power Dissipation (example calculation is in section 1 above)
T_A = 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 31.8°C/W per Table 6 below.
Therefore, Tj for an ambient temperature of 85°C with all outputs switching is:
85°C + 1.166W * 31.8°C/W = 122.1°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 (single layer or multi-layer).
Table 6. Thermal Resistance θ_JA for 64 Lead TQFP, E-Pad Forced Convection
θ_JA Vs. Air Flow
Meters per Second
0
1
Multi-Layer PCB, JEDEC Standard Test Boards
31.8°C/W
25.8°C/W
2.5
24.2°C/W
FEMTOCLOCKS™ VCXO-PLL FREQUENCY GENERATOR
22
ICS813078BYI REV. A OCTOBER 6, 2008