ICS843N252-45 Datasheet, PDF (11/16 Pages) Integrated Device Technology – Fourth generation FemtoClock

ICS843N252-45 Data Sheet
FEMTOCLOCK^® CRYSTAL-TO-3.3V LVPECL FREQUENCY SYNTHESIZER
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 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 + 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 94.8°C/W per Table 7 below.
Therefore, Tj for an ambient temperature of 70°C with all outputs switching is:
70°C + 0.485W * 94.8°C/W = 116°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 7. Thermal Resistance θ_JA for 16 Lead TSSOP Forced Convection
θ_JA by Velocity
Meters per Second
0
Multi-Layer PCB, JEDEC Standard Test Boards
94.8°C/W
1
90.4°C/W
2.5
88.3°C/W
ICS843N252GG-45 REVISION A JULY 6, 2011
11
©2011 Integrated Device Technology, Inc.