TLE42794_14 Datasheet, PDF (26/32 Pages) Infineon Technologies AG – Very low Current Consumption

TLE42794
Application Information
6.3
Thermal Considerations
Knowing the input voltage, the output voltage and the load profile of the application, the total power dissipation
can be calculated:
(4)
P_D = (V_I – V_Q) × I_Q + V_I × I_q
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:
(5)
R_{thJA, max}
=
T----_{j--,--m----a--x----}–_-----T----a
P_D
with
• T_j,max: maximum allowed junction temperature
• T_a: ambient temperature
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 = 50 mA
T_a = 105 °C
Calculation of R_thJA,max:
P_D = (V_I – V_Q) • I_Q + V_I • I_q
= (13.5 V – 5 V) • 50 mA + 13.5 V • 8 mA
= 0.425 W + 0.108 W
= 0.533 W
R_thJA,max = (T_j,max – T_a) / P_D
= (150 °C – 105 °C) / 0.533 W
= 84.4 K/W
As a result, the PCB design must ensure a thermal resistance R_thJA lower than 84.4 K/W. By considering
TLE42794E (PG-SSOP-14 EP package) and according to “Thermal Resistance” on Page 10, at least 300 mm²
heatsink area is needed on the FR4 1s0p PCB, or the FR4 2s2p board can be used.
Data Sheet
26
Rev. 1.2, 2014-07-03