ICS853111B Datasheet, PDF (13/19 Pages) Integrated Circuit Systems – LOW SKEW, 1-TO-10 DIFFERENTIAL-TO-2.5V/3.3V LVPECL/ECL FANOUT BUFFER

ICS853111B
LOW SKEW, 1-TO-10, DIFFERENTIAL-TO-2.5V, 3.3V LVPECL/ECL FANOUT BUFFER
POWER CONSIDERATIONS
This section provides information on power dissipation and junction temperature for the ICS853111B.
Equations and example calculations are also provided.
1. Power Dissipation.
The total power dissipation for the ICS853111B is the sum of the core power plus the power dissipated in the load(s).
The following is the power dissipation for V = 3.8V, 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 = 3.8V * 120mA = 456mW
MAX
CC_MAX
EE_MAX
• Power (outputs) = 30.94mW/Loaded Output pair
MAX
If all outputs are loaded, the total power is 10 * 30.94mW = 309.4mW
Total Power (3.8V, with all outputs switching) = 456mW + 309.4mW = 765.4mW
_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
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 200 linear feet per minute and a multi-layer board, the appropriate value is 43.8°C/W per Table 6 below.
Therefore, Tj for an ambient temperature of 70°C with all outputs switching is:
70°C + 0.765W * 43.8°C/W = 118.5°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 6. THERMAL RESISTANCE θ FOR 32-PIN TQFP, E-PAD FORCED CONVECTION
JA
θ by Velocity (Linear Feet per Minute)
JA
Single-Layer PCB, JEDEC Standard Test Boards
Multi-Layer PCB, JEDEC Standard Test Boards
0
69.3°C/W
49.5°C/W
200
57.8°C/W
43.8°C/W
500
52.1°C/W
41.3°C/W
NOTE: Most modern PCB designs use multi-layered boards. The data in the second row pertains to most designs.
IDT^™ / ICS^™ 1-TO-10, LVPECL/ECL FANOUT BUFFER
13
ICS853111BY REV. B SEPTEMBER 5, 2007