ICS85320I Datasheet, PDF (10/14 Pages) Integrated Circuit Systems – LVCMOS / LVTTL-TO-DIFFERENTIAL 2.5V / 3.3V LVPECL TRANSLATOR

Integrated
Circuit
Systems, Inc.
ICS85320I
LVCMOS / LVTTL-TO-DIFFERENTIAL
2.5V / 3.3V LVPECL TRANSLATOR
POWER CONSIDERATIONS
This section provides information on power dissipation and junction temperature for the ICS85320I.
Equations and example calculations are also provided.
1. Power Dissipation.
The total power dissipation for the ICS85320I 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 + 5% = 3.465V, which gives worst case results.
NOTE: Please refer to Section 3 for details on calculating power dissipated in the load.
• Power (core) = V
*I
= 3.465V * 25mA = 86.6mW
MAX
CC_MAX EE_MAX
• Power (outputs)_MAX = 30.2mW/Loaded Output pair
Total Power (3.465V, with all outputs switching) = 86.6mW + 30.2mW = 116.6mW
_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 103.3°C/W per Table 5 below.
Therefore, Tj for an ambient temperature of 85°C with all outputs switching is:
85°C + 0.117W * 103.3°C/W = 97.1°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 5. THERMAL RESISTANCE θ_JA FOR 8-PIN SOIC, FORCED CONVECTION
θ_JA by Velocity (Linear Feet per Minute)
Single-Layer PCB, JEDEC Standard Test Boards
Multi-Layer PCB, JEDEC Standard Test Boards
0
153.3°C/W
112.7°C/W
200
128.5°C/W
103.3°C/W
500
115.5°C/W
97.1°C/W
NOTE: Most modern PCB designs use multi-layered boards.The data in the second row pertains to most designs.
85320AMI
www.icst.com/products/hiperclocks.html
10
REV. A AUGUST 25, 2004