TLE4678_15 Datasheet, PDF (32/37 Pages) Infineon Technologies AG – Low Drop Out Linear Voltage Regulator

TLE4678
Application Information
9.3
Thermal Considerations
Knowing the input voltage, the output voltage and the load profile of the application, the total power
dissipation can be calculated:
P_D = (V_I – V_Q) × I_Q + V_I × I_q
(9.1)
with
• P_D: continuous power dissipation
• V_I: input voltage
• V_Q: output voltage
• I_Q: output current
• I_q: quiescent current
The maximum acceptable thermal resistance R_thJA can then be calculated:
R_{thJA, max}
=
T----_{j--,--m----a--x----}–_-----T----a
P_D
with
• T_j,max: maximum allowed junction temperature
• T_a: ambient temperature
(9.2)
Based on the above calculation the proper PCB type and the necessary heat sink area can be determined with
reference to the specification in “Thermal Resistance” on Page 10.
Example
Application conditions:
V_I = 13.5 V
V_Q = 5 V
I_Q = 150 mA
T_a = 75 °C
Calculation of R_thJA,max:
P_D = (V_I – V_Q) × I_Q + V_I × I_q
= (13.5V – 5V) × 150 mA + 13.5 V × 8 mA
= 1.275 W + 0.108 W
= 1.383 W
R_thJA,max = (T_j,max – T_a) / P_D
= (150 °C – 75 °C) / 1.383 W
= 54.2 K/W
Datasheet
32
Rev. 1.2, 2014-10-17