8535AG-21

www.icst.com/products/hiperclocks.html

REV. A OCTOBER 20, 2004

10

Integrated

Circuit

Systems, Inc.

ICS8535-21

This section provides information on power dissipation and junction temperature for the ICS8535-21.

Equations and example calculations are also provided.

1. Power Dissipation.

The total power dissipation for the ICS8535-21 is the sum of the core power plus the power dissipated in the load(s).

The following is the power dissipation for V

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 x 30mW = 60mW

Total Power

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 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)

T

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

θ

moderate air low of 200 linear feet per minute and a multi-layer board, the appropriate value is 85.5°C/W per Table 6 below.

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

70°C + 0.233W * 85.5°C/W = 90°C. This is well below the limit of 125°C.

This calculation is only an example, and the Tj will obviously vary depending on the number of outputs that are loaded, supply

voltage, air flow, and the type of board (single layer or multi-layer).

θθθθθ

θθθθθ

JA

FOR

0

200

500

Single-Layer PCB, JEDEC Standard Test Boards

146.4°C/W

125.2°C/W

112.1°C/W

Multi-Layer PCB, JEDEC Standard Test Boards

93.2°C/W

85.5°C/W

81.2°C/W

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