AAT4674_08 Datasheet, PDF (8/12 Pages) Advanced Analogic Technologies – Power Supply Selector Switch

SmartSwitch^TM
Functional Block Diagram
IN1
IIN1
SEL
IIN2
IN2
Thermal
and Current
Sense
Switch 1
Logic
Control
Switch 2
PRODUCT DATASHEET
AAT4674
Power Supply Selector Switch
OUT
EN
GND
Truth Table
Y = Yes, N = No, X = don’t care.
V_IN1 > UVLO
N
Y
N
Y
Y
Input Conditions
V_IN2 > UVLO
N
N
Y
Y
Y
SEL
X
X
X
0
1
AAT4674
V_OUT
Floating
Floating
Floating
V_IN1
V_IN2
AAT4674-1
V_OUT
Floating
V_IN1
V_IN2
V_IN1
V_IN2
Functional Description
To power the output, both input supplies (IN1 and IN2)
must be above the UVLO threshold. If either supply input
is below the UVLO threshold then the output will float or,
in the case of the AAT4674-1 the output will be the input
supply that is above the UVLO threshold. If both supplies
are above the UVLO threshold and the device is enabled,
the AAT4674/AAT4674-1 will connect the supply from IN1
to OUT when the SEL pin is LOW (logic ‘0’), and when the
SEL pin is HIGH (logic ‘1’) then the supply on IN2 is con-
nected to the OUT pin. Consult the above “Truth Table” for
the summarized AA4674/4674-1 operational details.
The two internal power switches are current limited and
the limiting thresholds can be programmed through the
resistors on the IIN1 and IIN2 pins respectively.
Applications Information
Input Capacitors
A 1μF or greater capacitor is generally recommended
between IN1 and GND (C_IN1), and between IN2 and GND
(C_IN2). An input capacitor is not required for basic opera-
tion; however, it is useful in preventing load transients
from affecting up-stream circuits. Ceramic, tantalum, or
aluminum electrolytic capacitors may be selected for C_IN1/
C_IN2. There is no specific capacitor equivalent series resis-
tance (ESR) requirement for C_IN1/C_IN2. However, for higher
current operation, ceramic capacitors are recommended
for C_IN1/C_IN2 due to their inherent capability over tantalum
capacitors to withstand input current surges from low
impedance sources such as batteries in portable devices.
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4674.2008.02.1.1