AMC DOC. #: AMC7585_E (LF)
AMC7585
Feb
2005
5A LOW DROPOUT REGULATOR
Copyright
© 2002, ADD Microtech Corp.
7
www.addmtek.com
Application Note:
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
OC, 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
oC), additional heat sink is required to control the junction temperature below 125 OC.
The junction temperature is: TJ = PD (θJT + θCS + θSA ) + TA
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 (°C / W )
59
45
38
33
27
24
21
PCB heat sink size (mm
2) 500
1000
1500
2000
3000
4000
5000
Recommended figure of PCB area used as a heat sink.
through hole vias
(Bottom View)
(Top View)
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