ICS844001-21 Datasheet, PDF (13/17 Pages) Integrated Device Technology – FEMTOCLOCKS™ CRYSTAL-TO-LVDS FREQUENCY SYNTHESIZER

ICS844001-21
FEMTOCLOCKS™ CRYSTAL-TO-LVDS 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 82.3°C/W per Table 7 is:
70°C + 0.581W * 82.3°C/W = 118°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 7. THERMAL RESISTANCE θ FOR 24-TSSOP, FORCED CONVECTION
JA
θ by Velocity (Meters per Second)
JA
Multi-Layer PCB, JEDEC Standard Test Boards
0
82.3°C/W
1
78°C/W
2.5
75.9°C/W
IDT^™ / ICS^™ INSERT PRODUCT NAME
13
ICS844001AG-21 REV. A SEPTEMBER 14, 2007