AND8391-D Datasheet, PDF (3/8 Pages) ON Semiconductor – Thermal Considerations for the ON Semiconductor

AND8391/D
Figure 3 shows power dissipation over changes in
ambient temperature for the SOT−223 package. Figure 4
shows q_JA (°C/W) and P_D (W) for various Cu areas and
thicknesses. These tables and graphs illustrate the effect of
Cu area, thickness and ambient temperature (T_A ) over the
range of −40°C to 85°C which encompasses the area of
interest for automotive LED operation.
NOTE: 300 mm² 2 oz Cu area has better thermal
performance than 500 mm² 1 oz Cu for this package.
2200
2000
1800
1600
1400
1200
1000
500 mm² 2 oz
300 mm² 2 oz
500 mm² 1 oz
300 mm² 1 oz
100 mm² 1 oz
P_D max @ 855C
500 mm² 2 oz Cu
300 mm² 2 oz Cu
500 mm² 1 oz Cu
300 mm² 1 oz Cu
100 mm² 2 oz Cu
100 mm² 1 oz Cu
722 mW
676 mW
631 mW
598 mW
559 mW
494 mW
800
600
100 mm² 2 oz
400
−40
−20
0
20
40
60
80
T_A, AMBIENT TEMPERATURE (°C)
Figure 3. Power Dissipation vs. Ambient
Temperature (SOT−223) @ T_J = 1505C
180
160
140
120
100
80
60
40
20
0
0
q_JA 1.0 oz Cu
1.5
Power Curve 2.0 oz Cu
1.4
Power Curve 1.0 oz Cu ^1.3
1.2
1.1
q_JA 2.0 oz Cu
1
0.9
0.8
T_A = 25°C
0.7
100 200 300 400 500 600 700
COPPER HEAT SPREADER AREA (mm²)
Figure 4. SOT−223 q_JA and P_D vs. Cu Area
PC board design and the use of multilayer board material
will affect the thermal performance. See ON Semiconductor
application notes AND8220/D and AND8222/D for further
information.
Ambient operating temperature (T_A) and estimated
device power will help determine which package to use.
Figures 2 and 4 can be used to quickly determine which
package and heat sink is a good candidate for the application.
Current Regulation: Pulse Mode vs. Steady−State
NOTE: All curves are based upon a typical 30 mA CCR
device.
There are two methods of measuring current regulation:
Pulse mode (_Ireg(P)) testing is applicable for factory and
incoming inspection of a CCR where the test times are a
minimum (t v 300 ms). DC steady−state (I_reg(SS)) testing is
applicable for application verification where the CCR will
be operational for seconds, minutes or hours.
ON Semiconductor has correlated the difference in I_reg(P) to
I_reg(SS) for stated board material, size, copper area and
copper thickness. I_reg(P) will always be greater than I_reg(SS)
due to the die temperature rising during I_reg(SS). This heating
effect can be minimized during circuit design with the
correct selection of board material, metal trace size and
weight for the operating current, voltage, and board
operating temperature (T_A) and package. (Refer to the
Thermal Characteristics table in datasheet).
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