Datasheet

MIC5209
DS20005720A-page 14  2017 Microchip Technology Inc.
the number of clock outputs, and the type of level
shifter (from core logic levels to 2.5V levels). Intel
estimates a “worst-case” load of 320 mA.
The MIC5209 was designed to provide the 2.5V power
requirement for Slot-1 applications. Its guaranteed
performance of 2.5V ±3% at 500 mA allows adequate
margin for all systems, and the dropout voltage of
500 mV means that it operates from a “worst-case”
3.3V supply where the voltage can be as low as 3.0V.
FIGURE 4-5: Slot-1 Power Supply.
A Slot-1 power supply (Figure 4-5) is easy to
implement. Only two capacitors are necessary, and
their values are not critical. C
IN
bypasses the internal
circuitry and should be at least 0.1 µF. C
OUT
provides
output filtering, improves transient response, and
compensates the internal regulator control loop. Its
value should be at least 22 µF. C
IN
and C
OUT
can be
increased as much as desired.
4.10.1 SLOT-1 POWER SUPPLY POWER
DISSIPATION
Powered from a 3.3V supply, the Slot-1 power supply
illustrated in Figure 4-5 has a nominal efficiency of
75%. At the maximum anticipated Slot-1 load
(320 mA), the nominal power dissipation is only
256 mW.
The SOT-223 package has sufficient thermal
characteristics for wide design margins when mounted
on a single-layer copper-clad printed circuit board. The
power dissipation of 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:
EQUATION 4-2:
So:
EQUATION 4-3:
Resulting in:
EQUATION 4-4:
Using the maximum junction temperature of +125°C
and a θ
JC
of 15°C/W for the SOT-223, 25°C/W for the
SOIC-8, or 3°C/W for the DDPAK package, the
following worst-case heat-sink thermal resistance (θ
SA
)
requirements are:
EQUATION 4-5:
Table 4-2 and Figure 4-6 show that the Slot-1 power
supply application can be implemented with a minimum
footprint layout.
Figure 4-6 shows the necessary copper pad area to
obtain specific heatsink thermal resistance (θ
SA
)
values. The θ
SA
values highlighted in Ta bl e 4-2 require
much less than 500 mm
2
of copper and, per Figure 4-6,
can be easily accomplished with the minimum footprint.
MIC5209-x.xYS
V
IN
13
2, TAB
IN OUT
GND
V
OUT
C
IN
0.1μF
C
OUT
22μF
V
IN MAX
V
OUT MAX
–I
OUT
 V
IN MAX
+ I
GND

TABLE 4-2: MAXIMUM ALLOWABLE
THERMAL RESISTANCE
T
A
+40°C +50°C +60°C +70°C
θ
JA
Limit 209°C/W 184°C/W 160°C/W 135°C/W
θ
SA
SOT-223
194°C/W 169°C/W 145°C/W 120°C/W
θ
SA
SOIC-8
184°C/W 159°C/W 135°C/W 110°C/W
θ
SA
DDPAK
206°C/W 181°C/W 157°C/W 132°C/W
3.6V 2.375V–320mA3.6V 4mA+
P
D
407mW=

JA
T
JMAX
T
A
–
P
D
--------------------------------=
Where: θ
SA
= θ
JA
- θ
JC