AAT4250
Slew Rate Controlled Load Switch
Functional Block Diagram
IN
Slew Rate
Control
OUT
Under-
Voltage
Lockout
Level
Shift
ON/OFF
GND
Functional Description
The AAT4250 is a slew rate controlled P-channel
MOSFET power switch designed for high-side load
switching applications. It operates with input volt-
ages ranging from 1.8V to 5.5V which, along with its
extremely low operating current, makes it ideal for
battery-powered applications. In cases where the
input voltage drops below 1.8V, the AAT4250 MOS-
FET is protected from entering the saturated region
of operation by automatically shutting down. In
addition, the TTL compatible ON/OFF pin makes
the AAT4250 an ideal level-shifted load switch. The
slew rate controlling feature eliminates inrush cur-
rent when the MOSFET is turned on, allowing the
AAT4250 to be used with a small input capacitor, or
no input capacitor at all. During slewing, the current
ramps linearly until it reaches the level required for
the output load condition. The proprietary control
method works by careful control and monitoring of
the MOSFET gate voltage. When the device is
switched ON, the gate voltage is quickly increased
to the threshold level of the MOSFET. Once at this
level, the current begins to slew as the gate voltage
is slowly increased until the MOSFET becomes fully
enhanced. Once it has reached this point, the gate
is quickly increased to the full input voltage and
R
DS(ON)
is minimized.
8
Applications Information
Input Capacitor
A 1µF or larger capacitor is typically recommended
for C
IN
in most applications. A C
IN
capacitor is not
required for basic operation; however, it is useful in
preventing load transients from affecting upstream
circuits. C
IN
should be located as close to the
device V
IN
pin as practically possible. Ceramic,
tantalum, or aluminum electrolytic capacitors may
be selected for C
IN
. There is no specific capacitor
equivalent series resistance (ESR) requirement for
C
IN
. However, for higher current operation, ceram-
ic capacitors are recommended for C
IN
due to their
inherent capability over tantalum capacitors to with-
stand input current surges from low-impedance
sources, such as batteries in portable devices.
Output Capacitor
For proper slew operation, a 0.1µF capacitor or
greater is required between V
OUT
and GND.
Likewise, with the output capacitor, there is no spe-
cific capacitor ESR requirement. If desired, C
OUT
may be increased without limit to accommodate
any load transient condition without adversely
affecting the slew rate.
4250.2006.03.1.3
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
