AMC7140 Datasheet, PDF (7/9 Pages) ADDtek Corp – 700mA HIGH VOLTAGE ADJUSTABLE CURRENT REGULATOR WITH ENABLE CONTROL

AMC7140
THERMAL CONSIDERATION
The Maximum Power Dissipation on Current Regulator:
P_D(MAX) = V_OUT(MAX) × I_OUT(NOM) + V_IN(MAX) × I_DD
V_OUT(MAX) = the maximum voltage on output pin;
I_OUT(NOM) = the nominal output current;
I_DD = the quiescent current the regulator consumes at I_OUT(NOM);
V_IN(MAX) = the maximum input voltage.
Thermal Consideration:
The AMC7140 has 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 AMC7140 prevents the device from damage due to excessive power
dissipation. When the device junction temperature rises to approximately 150°C, the regulator will be turned off. When
power consumption is over about 1000mW (TO-252 package, at T_A=70°C), additional heat sink is required to control
the junction temperature below 125°C.
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.
For TO-252 package, θ_JT = 7.0 oC /W.
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 θSA (°C /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.
Heat-pad of TO-252
Through hole vias
5
OUT
4
OE
3
GND
2
ISET
1
VDD
Copyright © 2007 ADDtek Corp.
7
DD032_B -- APRIL 2007