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©2016 Integrated Device Technology, Inc.

Revision D, June 15, 2016

8T73S208 Datasheet

Power Considerations

This section provides information on power dissipation and junction temperature for the 8T73S208.

Equations and example calculations are also provided.

1.

Power Dissipation.

The total power dissipation for the 8T73S208 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 8 * 36.3mW = 290.4mW

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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 is 125°C. Limiting the internal transistor junction temperature, Tj, to 125°C ensures that the bond

wire and bond pad temperature remains below 125°C.

The equation for Tj is as follows: Tj =



Tj = Junction Temperature



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



a multi-layer board, the appropriate value is 42.7°C/W per Table 6 below.

Therefore, Tj for an ambient temperature of 85°C with all outputs switching is:

85°C + 0.666W * 42.7°C/W = 113.4°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).

Table 6. Thermal Resistance





Meters per Second

01

2.5

Multi-Layer PCB, JEDEC Standard Test Boards

42.7°C/W

37.3°C/W

33.5°C/W