841N4830 Datasheet, PDF (21/28 Pages) Integrated Device Technology – Fourth generation FemtoClock

841N4830 DATA SHEET
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 for devices 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 = _JA * Pd_total + T_A
Tj = Junction Temperature
_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 _JA must be used. Assuming no air flow and
a multi-layer board, the appropriate value is 37.7°C/W per Table 7 below.
Therefore, Tj for an ambient temperature of 85°C with all outputs switching is:
85°C + 0.824W *37.7°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 _JA for 32 Lead VFQFN, Forced Convection
_JA by Velocity
Meters per Second
0
Multi-Layer PCB, JEDEC Standard Test Boards
37.7°C/W
1
32.9°C/W
2.5
29.5°C/W
Rev E 7/1/15
21
FEMTOCLOCK® NG CRYSTAL-TO-HCSL FREQUENCY SYNTHESIZER