ICS843SDN

FEMTOCLOCK™CRYSTAL-TO-3.3V LVPECL CLOCK GENERATOR

IDT™ / ICS™ 3.3V LVPECL CLOCK GENERATOR

10

ICS843SDNAG REV. A FEBRUARY 19, 2009

Power Considerations

This section provides information on power dissipation and junction temperature for the ICS843SDN.

Equations and example calculations are also provided.

1.

Power Dissipation.

The total power dissipation for the ICS843SDN is the sum of the core power plus the power dissipated in the load(s).

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

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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

and a multi-layer board, the appropriate value is 129.5°C/W per Table 7 below.

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

70°C + 0.318W * 129.5°C/W = 111.2°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 (multi-layer).

θ

Meters per Second

01

2.5

Multi-Layer PCB, JEDEC Standard Test Boards

129.5°C/W

125.5°C/W

123.5°C/W