ICS8735-21

700MHZ, DIFFERENTIAL-TO-3.3V LVPECL ZERO DELAY CLOCK GENERATOR

IDT™ / ICS™ 3.3V LVPECL ZERO DELAY CLOCK GENERATOR

15

ICS8735AM-21 REV. A JULY 31, 2008

Power Considerations

This section provides information on power dissipation and junction temperature for the ICS8735-21.

Equations and example calculations are also provided.

1.

Power Dissipation.

The total power dissipation for the ICS8735-21 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.

•

•

If all outputs are loaded, the total power is 2 * 30mW = 60mW

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 83.2°C/W per Table 7A below.

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

70°C + 0.580W * 83.2°C/W = 118.3°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).

θ

Linear Feet per Minute

0200

500

Single-Layer PCB, JEDEC Standard Test Boards

83.2°C/W

65.7°C/W

57.5°C/W

Multi-Layer PCB, JEDEC Standard Test Boards

46.2°C/W

39.7°C/W

36.8°C/W

NOTE: Most modern PCB designs use multi-layered boards. The data in the second row pertains to most designs.

θ

Meters per Second

01

2.5

Multi-Layer PCB, JEDEC Standard Test Boards

37.0°C/W

32.4°C/W

29.0°C/W