AAT4651 Datasheet, PDF (7/14 Pages) Advanced Analogic Technologies – 5V/3V PC Card Power Switch

Functional Block Diagram
V_CC3
AAT4651
5V/3V PC Card Power Switch
V_CC5
Body Control
V_CC
Over-
Current
Over-
Temperature
Slew
Rate
VCCD1
VCCD0
Control
Logic
Over-
Current
Slew
Rate
80 Ω
FAULT
GND
Functional Description
The AAT4651 is a single channel power switch that
can be used in any application where dual power
supply multiplexing is required. Typical applications
for this include PC card applications not requiring a
12V power supply, or applications where power is
switched, for example, between 5V for operation
and 3.3V for standby mode. The AAT4651 operates
with input voltages ranging from 2.7V to 5.5V in any
combination and automatically powers its internal
circuitry from whichever input voltage is higher. Two
identical low R_DS(ON) P-channel MOSFETs serve as
the power multiplexing circuit with a common drain
as the V_CC output and independent sources as the
two V_CC3 and V_CC5 inputs. A 2-bit parallel interface
determines the state of the multiplexer: V_CC = V_CC3,
V_CC = V_CC5, or V_CC with resistive pull down to
ground. When the state is set to either of the two
inputs, the multiplexing circuit will slowly slew the
4651.2006.05.1.2
V_CC output to the new voltage level which protects
the upstream power supply from sudden load tran-
sients. When the resistive pull down is chosen for
V_CC, the V_CC output is quickly discharged by the
resistive pull down. The AAT4651 always serves as
an electronic fuse by limiting the load current if it
exceeds the current limit threshold. During power-
up into a short, the current will gradually increase
until the current limit is reached. During a sudden
short circuit on the output, the current limit will
respond in 1µs to isolate and protect the upstream
power supply from the load short circuit. In most
applications, because the response time is so fast,
a short circuit to V_CC will not affect the upstream
supply, so system functionality will not be affected.
In the case of an over-current condition, an open
drain FAULT flag output will signal the event. The
FAULT output is also active during output voltage
slew, and becomes inactive once the output is with-
in regulation.
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