ICS844071

FEMTOCLOCK™CRYSTAL-TO-LVDS CLOCK GENERATOR

IDT™ / ICS™ LVDS CLOCK GENERATOR

11

ICS844071AG SEPTEMBER 26, 2007

Power Considerations

This section provides information on power dissipation and junction temperature for the ICS844071.

Equations and example calculations are also provided.

1.

Power Dissipation.

The total power dissipation for the ICS844071 is the sum of the core power plus the analog power plus the power dissipated in the load(s).

NOTE: Please refer to Section 3 for details on calculating power dissipated in the load.

•

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 devices is 125°C.

The equation for Tj is as follows: Tj =

θ

Tj = Junction Temperature

θ

Pd_total = Total Device Power Dissipation (example calculation is in section 1 above)

In order to calculate junction temperature, the appropriate junction-to-ambient thermal resistance

θ

air flow of 1 meter per second and a multi-layer board, the appropriate value is 90.5°C/W per Table 6 below.

Therefore, Tj for an ambient temperature of 70°C with all outputs switching is:

70°C + 0.533W * 90.5°C/W = 118.3°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).

θ

Meters per Second

01

2.5

Multi-Layer PCB, JEDEC Standard Test Boards

101.7°C/W

90.5

89.8