AMC1112 Datasheet, PDF (6/8 Pages) ADDtek Corp – 1A LOW DROPOUT POSITIVE REGULATOR

Application Note:
AMC1112
Maximum Power Calculation:
P_D(MAX)=
T_J(MAX) – T_A(MAX)
θ_JA
T_J(^OC): Maximum recommended junction temperature
T_A(^OC): Ambient temperature of the application
θ_JA(^OC/W): Junction-to-junction temperature thermal resistance of the package, and other heat dissipating
materials.
The maximum power dissipation of a single-output regulator :
P_D(MAX) = [(V_IN(MAX) - V_OUT(NOM))] × I_OUT(NOM) + V_IN(MAX) × I_Q
Where: V_OUT(NOM) = the nominal output voltage
I_OUT(NOM) = the nominal output current, and
I_Q = the quiescent current the regulator consumes at I_OUT(MAX)
V_IN(MAX) = the maximum input voltage
Then θ_JA = (150 ^OC – T_A)/ P_D
Thermal consideration:
When power consumption is over about 404 mW ( for SOT-223 package, 687mW for TO-252 package, at T_A=70 ^OC),
additional heat sink is required to control the junction temperature below 125 ^OC.
The junction temperature is: T_J = P _D ( θ_JT + θ_CS + θ_SA ) + T_A
P _D :Dissipated power.
θ_JT :Thermal resistance from the junction to the mounting tab of the package.
θ_CS :Thermal resistance through the interface between the IC and the surface on which it is mounted. (typically,
θ_CS < 1.0°C/W)
θ_SA : Thermal resistance from the mounting surface to ambient (thermal resistance of the heat sink).
If PC Board copper is going to be used as a heat sink, below table can be used to determine the appropriate size of
copper foil required. For multi-layered PCB, these layers can also be used as a heat sink. They can be connected with
several through hole vias.
PCB θ_SA (^OC /W )
59
PCB heat sink size (mm²) 500
45
1000
38
1500
33
2000
27
3000
24
4000
21
5000
Recommended figure of PCB area used as a heat sink.
through hole vias
(Top View)
Copyright © 2007 ADDtek Corp
(Bottom View)
6
DD003_B -- MAY 2007