IDT / ICS 2.5V LVPECL FREQUENCY SYNTHESIZER
13
ICS843001AK-40 REV. A OCTOBER 10, 2007
ICS843001-40
FEMTOCLOCKS CRYSTAL-TO-2.5V LVPECL FREQUENCY SYNTHESIZER
POWER CONSIDERATIONS
This section provides information on power dissipation and junction temperature for the ICS843001-40.
Equations and example calculations are also provided.
1. Power Dissipation.
The total power dissipation for the ICS843001-40 is the sum of the core power plus the power dissipated in the load(s).
The following is the power dissipation for V
CC
= 2.5V + 5% = 2.625V, which gives worst case results.
NOTE: Please refer to Section 3 for details on calculating power dissipated in the load.
Power (core)
MAX
= V
CC_MAX
* I
EE_MAX
= 2.625V * 80mA = 210mW
Power (outputs)
MAX
= 30mW/Loaded Output pair
Total Power
_MAX
= 210mW + 30mW = 240mW
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
JA * Pd_total + TA
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 74.9°C/W per Table 6 below.
Therefore, Tj for an ambient temperature of 70°C with all outputs switching is:
70°C + 0.240W * 74.9°C/W = 87.9°C. This is well 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
θθθθθ
JA
FOR
16-PIN VFQFN, FORCED CONVECTION
θθθθθ
JA
vs. 0 Air Flow (Meters per Second)
0
1
2.5
Multi-Layer PCB, JEDEC Standard Test Boards
74.9°C/W
65.5°C/W
58.8°C/W