IDT / ICS 680MHZ, 3.3V LVPECL FREQUENCY SYNTHESIZER
10
ICS843202AYI REV. A MAY 16, 2007
ICS843202I
FEMTOCLOCKS 680MHZ, CRYSTAL-TO-3.3V DIFFERENTIAL LVPECL FREQUENCY SYNTHESIZER
θθθθθ
JA
by Velocity (Meter per Second)
0
1
2.5
Multi-Layer PCB, JEDEC Standard Test Boards
80.8°C/W
71.2°C/W
67.6°C/W
TABLE 6. THERMAL RESISTANCE
θθθθθ
JA
FOR
32-PIN LQFP, FORCED CONVECTION
POWER CONSIDERATIONS
This section provides information on power dissipation and junction temperature for the ICS843202I.
Equations and example calculations are also provided.
1. Power Dissipation.
The total power dissipation for the ICS843202I is the sum of the core power plus the power dissipated in the load(s).
The following is the power dissipation for V
CC
= 3.3V + 10% = 3.63V, 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
= 3.63V * 138mA = 500.9mW
Power (outputs)
MAX
= 30mW/Loaded Output pair
If all outputs are loaded, the total power is 2 * 30mW = 60mW
Total Power
_MAX
(3.63V, with all outputs switching) = 500.9mW + 60mW = 560.9mW
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
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 a
moderate air flow of 1 meter per second and a multi-layer board, the appropriate value is 71.2°C/W per Table 6 below.
Therefore, Tj for an ambient temperature of 85°C with all outputs switching is:
85°C + 0.561W * 71.2°C/W = 124.9°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).