ICS840001I-25 Datasheet, PDF (9/12 Pages) Integrated Device Technology – FEMTOCLOCK LVCMOS LVTTL CLOCK GENERATOR

ICS840001I-25
FEMTOCLOCK™ LVCMOS/LVTTL CLOCK 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^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 a
moderate air flow of 1meter per second and a multi-layer board, the appropriate value is 125.5°C/W per Table 5.
Therefore, Tj for an ambient temperature of 85°C with all outputs switching is:
85°C + 0.316W * 125.5°C/W = 124.7°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 (multi-layer).
TABLE 5. THERMAL RESISTANCE θ FOR 8-LEAD TSSOP, FORCED CONVECTION
JA
θ by Velocity (Meters Per Second)
JA
Multi-Layer PCB, JEDEC Standard Test Boards
0
129.5°C/W
1
125.5°C/W
2.5
123.5°C/W
IDT^™ / ICS^™ LVCMOS CLOCK GENERATOR
9
ICS840001BGI-25 REV. A MARCH 31, 2009