TLF80511EJ_15 Datasheet, PDF (16/20 Pages) Infineon Technologies AG – Low Dropout Linear Fixed Voltage Regulator

TLF80511EJ
Application Information
In case of rapid transients of input voltage or load current, the capacitance should be dimensioned in accordance
and verified in the real application that the output stability requirements are fulfilled.
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:
P_D = (V_I - V_Q) × I_Q + V_I × I_q
(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,max - T_a ) / P_D
(2)
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 7.
Example
Application conditions:
V_I = 13.5V
V_Q = 5V
I_Q = 120mA
T_a = 85°C
Calculation of R_thJA,max:
P_D = (V_I – V_Q) × I_Q + V_I × I_q
= (13.5V – 5V) × 120mA
(V_I × I_q can be neglected because of very low I_q)
= 1.02W
R_thJA,max = (T_j,max – T_a) / P_D
= (150°C – 85°C) / 1.02W = 63.73K/W
As a result, the PCB design must ensure a thermal resistance R_thJA lower than 63.73 K/W. According to “Thermal
Resistance” on Page 7, at least 600 mm² heatsink area is needed on the FR4 1s0p PCB, or the FR4 2s2p board
can be used.
Data Sheet
16
Rev. 1.0, 2014-11-17