ICS8440258-46 Datasheet, PDF (12/16 Pages) Integrated Device Technology – FEMTOCLOCK™ CRYSTAL/LVCMOS-TOLVDS/LVCMOS FREQUENCY SYNTHESIZER

ICS8440258-46
FEMTOCLOCK™ CRYSTAL/LVCMOS-TO-LVDS/ LVCMOS FREQUENCY SYNTHESIZER
PRELIMINARY
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^TM devices is 125°C.
The equation for Tj is as follows: Tj = θ * Pd_total + T
JA
A
Tj = Junction Temperature
θ = Junction-to-Ambient Thermal Resistance
JA
Pd_total = Total Device Power Dissipation (example calculation is in section 1 above)
T = Ambient Temperature
A
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 37°C/W per Table 6.
Therefore, Tj for an ambient temperature of 70°C with all outputs switching is:
70°C + 0.519W * 37°C/W = 89.2°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 (single layer or multi-layer).
TABLE 6. THERMAL RESISTANCE θ FOR 32-LEAD VFQFN, FORCED CONVECTION
JA
θ vs. Air Flow (Meters per Second)
JA
Multi-Layer PCB, JEDEC Standard Test Boards
0
37.0°C/W
1
32.4°C/W
2.5
29.0°C/W
IDT^™ / ICS^™ LVDS/LVCMOS FREQUENCY SYNTHESIZER
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ICS8440258AK-46 REV B JANUARY 15, 2008