AAT4674_08 Datasheet, PDF (10/12 Pages) Advanced Analogic Technologies – Power Supply Selector Switch

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For example, for a 2.5V input power supply application
that is specified to operate in 50°C environments where
the PCB operates at temperatures as high as 85°C. The
application is sealed and its PCB is small, causing R_θJA to
be approximately 160°C/W. The R_DS(ON)(MAX) is estimate to
be 300mΩ (from the “R_DS(ON) vs. Temperature” perfor-
mance graph, where V_IN = 2.5V at 85°C plus 50%). To
find the maximum current (I_MAX) for this application use
Equation 2:
I_MAX ⁼
125°C - 85°C
300mΩ · 160°C/W ^{= 0.913A}
PRODUCT DATASHEET
AAT4674
Power Supply Selector Switch
PCB Layout Recommendations
For proper thermal management, to minimize PCB trace
resistance, and to take advantage of the low R_DS(ON) val-
ues of the two internal power switches in the
AAT4674/4674-1, certain circuit board layout rules
should be followed: IN1, IN2, and OUT should be routed
using wider than normal traces. The two IN1 pins (1 and
2) and two IN2 pins (3 and 4) should be connected to
the same wide PCB trace; and GND should be connected
to a ground plane. For best performance, the input
capacitors (C_IN1/C_IN2) and output capacitors (C_OUT) should
be placed as close to the package pins as possible. The
AAT4674/4674-1 evaluation board layout follows the
printed circuit board layout recommendations and can
be used as an example of an optimal board layout.
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4674.2008.02.1.1