Slew Rate Controlled Load Switch
Functional Block Diagram
IN
Under-
Voltage
Lockout
Level
Shift
Turn-On
Slew Rate
Control
AAT4280
OUT
*
ON/OFF
GND
*AAT4280-3 only
Functional Description
The AAT4280 is a family of flexible P-channel MOS-
FET power switches designed for high-side load
switching applications. There are three versions of
the AAT4280 with different turn-on and turn-off char-
acteristics to choose from, depending upon the spe-
cific requirements of an application. The first ver-
sion, the AAT4280-1, has a moderate turn-on slew
rate feature, which reduces inrush current when the
MOSFET is turned on. This function allows the load
switch to be implemented with either a small input
capacitor or no input capacitor at all. During turn-on
slewing, the current ramps linearly until it reaches
the level required for the output load condition. The
proprietary turn-on current 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.
The second version, the AAT4280-2, is a very fast
switch intended for high-speed switching applica-
tions. This version has no turn-on slew rate control
and no special output discharge features.
The final version, the AAT4280-3, has the addition
of a minimized slew rate limited turn-on function
and a shutdown output discharge circuit to rapidly
turn off a load when the load switch is disabled
through the ON/OFF pin.
All versions of the AAT4280 operate with input volt-
ages ranging from 1.8V to 5.5V. All versions of this
device have extremely low operating current, mak-
ing them ideal for battery-powered applications. In
cases where the input voltage drops below 1.8V,
the AAT4280 MOSFET device is protected from
entering into the saturation region of operation by
automatically shutting down through an under-volt-
age lockout control circuit. The ON/OFF control pin
is TTL compatible and will also function with 2.5V
to 5V logic systems, making the AAT4280 an ideal
level-shifting load switch.
4280.2006.11.1.4
9
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
