點晶科技股份有限公司
SILICON TOUCH TECHNOLOGY INC.
新竹市科學園區展業一路9號7樓之1
9-7F-1, Prosperity RoadⅠ, Hsin-Chu, Taiwan, R.O.C.
DD311
Tel：886-3-5645656
Fax：886-3-5645626
Power Dissipation
Notice that the power dissipation of a semiconductor chip is limited to its package and ambient
temperature, in which the device requires the maximum output current calculated for given
operating conditions. The maximum allowable power consumption can be calculated by the
following equation:
Tj(junction temperature)(max)(°C)– Ta(ambient temperature)(°C)
Pd(max)(Watt) =
Rth(junction-to-air thermal resistance)(°C/Watt)
The relationship between power dissipation and operating temperature can be refer to the figure
below:
5.0
4.5
Tj(max)=125 °C
4.0
Rth=23.38 °C/Watt
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
20
40
60
80
100
120
140
Ambient Temperature Ta(°C)
Based on the Pd(max), the maximum allowable voltage of output terminal can be calculated as
follows:
Pd(max)(Watt)– VREXT(Volt) × IREF(A)
Vout(max)(Volt) =
Iout(A) × Dimming Duty
HIGH CONSTANT CURRENT LED DRIVER
Version:A.002
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