AAT4650_06 Datasheet, PDF (7/14 Pages) Advanced Analogic Technologies – 5V/3V PC Card Power Switch

Functional Block Diagram
V_CC3
AAT4650
5V/3V PC Card Power Switch
V_CC5
Body Control
V_CC
Over-
Current
Over-
Temperature
Slew
Rate
C TL1
C TL0
Control
Logic
Over-
Current
Slew
Rate
5kΩ
FAULT
GND
Functional Description
The AAT4650 is a single channel power switch that
can be used in any application where dual power
supply multiplexing is required. Typical applications
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 AAT4650 operates
with input voltages ranging from 2.7V to 5.5V in any
combination and automatically powers its internal
circuitry off of 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, V_CC with resistive pull down to ground,
or V_CC high impedance. When the state is set to
either of the two inputs, the multiplexing circuit will
4650.2006.05.1.2
slowly slew the V_CC output to the new voltage level
which protects the upstream power supply from sud-
den load transients. When the resistive pull down is
chosen for V_CC, the V_CC output is quickly discharged
by the resistive pull down. The AAT4650 always
serves as an electronic fuse by limiting the load cur-
rent 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 out-
put voltage slew, and becomes inactive once the
output is within regulation.
7