APL5551 Datasheet, PDF (12/17 Pages) Anpec Electronics Coropration – Dual Channel 500mA/500mA Regulator + Reset IC

APL5551
Application Information
Thermal Protection (Cont.)
operation, do not exceed the junction temperature
rating of T_J=+150°C.
Operating Region and Power Dissipation
The thermal resistance of the case and circuit board,
ambient and junction air temperature, and the rate of
air flow all control the APL5551 maximum power
dissipation. The power dissipation across the device
is P = I (V -V ). The maximum power dissipation
OUT IN OUT
is:
applications. The thermal pad is soldered to the top
ground pad and is connected to the internal or bottom
ground plane by several vias. The printed circuit board
(PCB) forms a heat sink and dissipates most of the
heat into ambient air. The vias are recommended to
have proper size to retain solder, helping heat
conduction.
102 mil
P
MAX
=
(T -T )
JA
/
(θ_JB
+θ_BA )
where T_J-T_A is the temperature difference between the
junction and ambient air.
118 mil
SOP-8-P
θ_JB is the thermal resistance of the package, θ_BA is the
thermal resistance through the printed circuit board,
copper traces, and other materials to the surrounding
air. The GND pin provides an electrical connection to
ground and channeling heat away. Connect the GND
pin to ground using a large pad or ground plane as a
heat sink, it can improve maximize thermal dissipation.
For example:
The SOP8 package has maximum power dissipation
0.7W at TA= 55°C and 1.4W at SOP-8-P (see Power
dissipation vs Ambient Temperature).
Ambient
Air
Thermal
Die _pad
Top
ground
pad
Vias Internal Printed
ground circuit
plane board
Figure 1
VIN = 5V, IOUT = 250mA, VOUT1 = 3.3V, VOUT2 = 2.8V,
PD = [(5-3.3)V+(5-2.8)V] x 250mA = 0.975W
the PD = 0.975W
According the power dissipation issue, we should adapt
the SOP-8-P package. It could reduce the thermal
resistance to maintain the IC longer life.
See figure 1. The SOP-8-P utilizes a bottom thermal
pad to minimize the thermal resistance of the package,
making the package suitable for high current
Copyright © ANPEC Electronics Corp.
12
Rev. A.2 - Oct., 2005
www.anpec.com.tw