ICS854S204I Datasheet, PDF (14/19 Pages) Integrated Device Technology – LOW SKEW, DUAL, PROGRAMMABLE 1-TO-2 DIFFERENTIALTO-LVDS, LVPECL FANOUT BUFFER

ICS854S204I
LOW SKEW, DUAL, 1-TO-2 DIFFERENTIAL-TO-LVDS, LVPECL FANOUT BUFFER
POWER CONSIDERATIONS (LVPECL OUTPUTS)
This section provides information on power dissipation and junction temperature for the ICS854S204I.
Equations and example calculations are also provided.
1. Power Dissipation.
The total power dissipation for the ICS854S204I 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.
DD
NOTE: Please refer to Section 3 for details on calculating power dissipated in the load.
• Power (core) = V * I = 3.465V * 66mA = 228.69mW
MAX
DD_MAX
DD_MAX
• Power (outputs) = 32mW/Loaded Output pair
MAX
If all outputs are loaded, the total power is 4 * 32mW = 128mW
Total Power (3.465V, with all outputs switching) = 228.69mW + 128mW = 356.69mW
_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 92°C/W per Table 6A below.
Therefore, Tj for an ambient temperature of 85°C with all outputs switching is:
85°C + 0.357W * 92°C/W = 117.8°C. This is below the limit of 125°C.
TABLE 6A. THERMAL RESISTANCE θ FOR 16-LEAD TSSOP, FORCED CONVECTION
JA
θ by Velocity (Meters per Second)
JA
Multi-Layer PCB, JEDEC Standard Test Boards
0
92°C/W
1
87.6°C/W
2.5
85.5°C/W
IDT^™ / ICS^™ LVDS, LVPECL FANOUT BUFFER
14
ICS854S204BGI REV. A JUNE 4, 2008