TLE4309 datasheet(10/12 Pages) INFINEON

10 / 12 page

Datasheet

Rev. 1.0, 2007-03-20

TLE4309

4. Calculating the maximum power dissipation:

For calculating the maximum power dissipation, the minimum forward voltage sum of the

LEDs connected in series

F,MIN,total (= No.ofLEDs* VF,MIN) , the maximum supply

voltage

I,MAX , the IC current consumption Iq,MAX , as well as the the maximum output

current

Q,MAX needs to be considered. Hence, the maximum power dissipation PD,MAX

calculates:

D,MAX = (VI,MAX - VF,MIN,total)* IQ,MAX + VI,MAX * Iq,MAX

With assuming a maximum current consumption of 15 mA @

Q = 260 mA,

the

maximum power dissipation for the example is 1.28 W.

5. Thermal Resistance needed:

The thermal resistance from junction to ambient

th,j-a calculates:

th,j-a = (Tj,max - Ta,max) / PD,MAX

With allowing a junction temperature of 150 °C, the

th,j-a needed in our example would

be 50 K/W.

In case some copper area on the PCB is used as a heat sink, the area needed is

approximately 6 cm

2 (board in horizontal position, no airflow). If the area is not available,

several via holes to the GND-layer or to a heatsink area on the PCB backside help to

distribute the heat.

For additional information on the thermal resistance see Infineon’ s special subject book

“Thermal Resistance - Theory and Practice” including extended package information.

TLE4309 Datasheet(PDF) 10 Page - Infineon Technologies AG