A8113
AiT Semiconductor Inc.
HIGH POWER WHITE LED DRIVER
www.ait-ic.com
300mA ULTRA-LOW NOISE, ULTRA-FAST
The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of
surroundings airflow and temperature difference between junction to ambient. The maximum power
dissipation can be calculated by following formula：
PD(MAX) = ( TJ(MAX) − TA ) /θJA
Where TJ(MAX) is the maximum operation junction temperature 125°C, TA is the ambient temperature and theθ
θJA is the junction to ambient thermal resistance. For recommended operating conditions specification of
A8113, where TJ(MAX) is the maximum junction temperature of the die(125°C) and TA is the maximum ambient
temperature. The junction to ambient thermal resistance (θJA is layout dependent) for SOT-25 package is
250°C/W, SC-70-5 package is 333°C/W, on standard JEDEC 51-3 thermal test board. The maximum power
dissipation at TA= 25°C can be calculated by following formula:
P
D(MAX) = (125°C−25°C)/333 = 300mW(SC-70-5)
D(MAX) = (125°C−25°C)/250 = 400mW(SOT-25)
P
The maximum power dissipation depends on operating ambient temperature for fixed TJ(MAX) and thermal
resistance θJA. It is also useful to calculate the junction of temperature of the A8113 under a set of specific
conditions. In this example let the Input voltage VIN=3.3V, the output current IO=300mA and the case
temperature TA=40°C measured by a thermal couple during operation. The power dissipation for the VO=2.8V
version of the A8113 can be calculated as:
PD = (3.3V−2.8V) ×300mA+3.6V×100uA=150mW
And the junction temperature, TJ, can be calculated as follows:
TJ=TA+PD×θJA=40°C+0.15W×250°C/W=40°C+37.5°C=77.5°C<TJ(MAX) =125°C
For this operating condition, TJ is lower than the absolute maximum operating junction temperature,125°C, so
it is safe to use the A8113 in this configuration.
REV2.0
- JUN 2011 RELEASED, SEP 2012 REVISED -
- 10 -
AITSEMI [ AiT Semiconductor ]
