AMC7585
APPLICATION INFORMATION
The maximum power dissipation of a single-output regulator:
PD(MAX) = [(VIN(MAX) - VOUT(NOM))] × IOUT(NOM) + VIN(MAX) × IQ
VOUT(NOM) = the nominal output voltage
IOUT(NOM) = the nominal output current, and
IQ = the quiescent current the regulator consumes at IOUT(MAX)
VIN(MAX) = the maximum input voltage
Thermal consideration:
The AMC7585 series have internal power and thermal limiting circuitry designed to protect the device under
overload conditions. However maximum junction temperature ratings should not be exceeded under continuous normal
load conditions. The thermal protection circuit of AMC7585 series will prevent the device from damage due to
excessive power dissipation. When the device temperature rises to approximately 150°C, the regulator will be turned
off.
When power consumption is over about 1.2W (for TO-220/ TO-263 package, 687mW for TO-252 package, at
TA=70 °C), additional heat sink is required to control the junction temperature below 125°C.
The junction temperature is: TJ = PD (θJT + θTS + θSA ) + TA
P D : Dissipated power.
θJT : Thermal resistance from the junction to the mounting tab of the package.
(For TO-220, TO-263, and TO-263-3 packages, θJT=6°C /W. For TO-252 package, θJT=7°C /W)
θTS : Thermal resistance through the interface between the IC and the surface on which it is mounted.
(typically, θCS < 1.0 °C / W)
θSA : 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.
59
500
45
1000
38
1500
33
2000
27
3000
24
4000
21
5000
PCB θSA (°C / W )
PCB heat sink size (mm2)
Recommended figure of PCB area used as a heat sink.
through hole vias
(Bottom View)
(Top View)
Copyright © 2007 ADDtek Corp.
7
DD041_G -- OCTOBER 2007
ADDTEK [ ADDTEK CORP ]
