AAT4674_12 Datasheet, PDF (10/12 Pages) Skyworks Solutions Inc. – Power Supply Selector Switch

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}
DATA SHEET
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-
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 AAT4674-1
evaluation board layout follows the printed circuit board
layout recommendations and can be used as an example
of an optimal board layout.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
10
201911A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • April 26, 2012