MIC5209
Micrel
the MIC5209 is calculated using the voltage drop across the
device × output current plus supply voltage × ground current.
Considering worst case tolerances, the power dissipation
could be as high as:
Table 2 and Figure 6 show that the Slot-1 power supply
application can be implemented with a minimum footprint
layout. Figure 6 shows the necessary copper pad area to
obtainspecificheatsinkthermalresistance(θ )values. The
SA
2
θ
values in Table 2 require much less than 500mm of
(V
– V
) × I
+ V
× I
IN(max) GND
SA
IN(max)
OUT(max)
OUT
copper, according to Figure 6, and can easily be accom-
plished with the minimum footprint.
[(3.6V – 2.375V) × 320mA] + (3.6V × 4mA)
P = 407mW
D
70
60
50
40
30
20
10
0
Using the maximum junction temperature of 125°C and a θ
JC
of 8°C/W for the SOT-223, 25°C/W for the SO-8, or 2°C/W for
the TO-263 package, the following worst-case heat-sink
thermal resistance (θ ) requirements are:
SA
T
− T
A
J(max)
θ
=
JA
P
D
θSA = θJA − θJC
0
2000
4000
6000
2
COPPER HEAT SINK AREA (mm )
TA
θJA (limit)
θSA SOT-223 201°C/W
θSA SO-8 184°C/W
θSA TO-263-5 207°C/W
40°C
50°C
60°C
75°C
Figure 6. PCB Heat Sink Thermal Resistance
209°C/W
184°C/W 160°C/W 123°C/W
176°C/W 152°C/W 115°C/W
159°C/W 135°C/W 98°C/W
182°C/W 158°C/W 121°C/W
Table 2. Maximum Allowable Thermal Resistance
MIC5209
10
August 2, 2000
MICREL [ MICREL SEMICONDUCTOR ]
