ICS843241I-04 Datasheet, PDF (10/14 Pages) Integrated Device Technology – FEMTOCLOCKS™ CRYSTAL-TO-3.3V, 2.5V LVPECL CLOCK GENERATOR

ICS843241I-04
FEMTOCLOCKS™ CRYSTAL-TO- 3.3V, 2.5V LVPECL CLOCK GENERATOR
POWER CONSIDERATIONS
PRELIMINARY
This section provides information on power dissipation and junction temperature for the ICS843241I-04.
Equations and example calculations are also provided.
1. Power Dissipation.
The total power dissipation for the ICS843241I-04 is the sum of the core power plus the power dissipated in the load(s).
The following is the power dissipation for V = 3.3V + 5% = 3.465V, which gives worst case results.
CC
NOTE: Please refer to Section 3 for details on calculating power dissipated in the load.
• Power (core) = V * I = 3.465V * 60mA = 207.9mW
MAX
CC_MAX
EE_MAX
• Power (outputs) = 30mW/Loaded Output pair
MAX
Total Power (3.465V, with all outputs switching) = 207.9mW + 30mW = 237.9mW
_MAX
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
+
T
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 129.5°C/W per Table 5 below.
Therefore, Tj for an ambient temperature of 85°C with all outputs switching is:
85°C + 0.238W * 129.5°C/W = 115.8°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 5. THERMAL RESISTANCE θ FOR 8-PIN 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^™ 150MHZ, 3.3V, 2.5V LVPECLCLOCK GENERATOR
10
ICS843241AGI-04 REV. A MAY 1, 2008