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AAT4252A-3 データシートの表示(PDF) - Analog Technology Inc

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AAT4252A-3
Analog-Technology
Analog Technology Inc Analog-Technology
AAT4252A-3 Datasheet PDF : 14 Pages
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AAT4252A
Dual Slew Rate Controlled Load Switch
Functional Description
The AAT4252A is a family of flexible dual P-chan-
nel MOSFET power switches designed for high-
side load switching applications. There are three
versions of the AAT4252A with different turn-on
and turn-off characteristics to choose from,
depending upon the specific requirements of an
application.
The first version, the AAT4252A-1, has a moderate
turn-on slew rate feature, which reduces in-rush
current when the MOSFET is turned on. This func-
tion 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 cur-
rent 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 the RDS(ON) is minimized.
The second version, the AAT4252A-2, is a very
fast switch intended for high-speed switching
applications. This version has no turn-on slew rate
control and no special output discharge features.
The final switch version, the AAT4252A-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 dis-
abled through the ON/OFF pin. Using the FAST
input pin on the AAT4252A-3, the device can be
manually switched to a slower slew rate.
All versions of the AAT4252A operate with input
voltages ranging from 1.5V to 6.5V. All versions of
this device have extremely low operating current,
making them ideal for battery-powered applications.
The ON/OFF control pin is TTL compatible and will
also function with 2.5V to 5V logic systems, mak-
ing the AAT4252A an ideal level-shifting load
switch.
4252A.2007.06.1.0
Applications Information
Input Capacitor
A 1μF or larger capacitor is typically recommended
for CIN in most applications. A CIN capacitor is not
required for basic operation; however, it is useful in
preventing load transients from affecting upstream
circuits. CIN should be located as close to the
device VIN pin as practically possible. Ceramic,
tantalum, or aluminum electrolytic capacitors may
be selected for CIN. There is no specific capacitor
equivalent series resistance (ESR) requirement for
CIN. However, for higher current CIN, ceramic
capacitors are recommended for CIN 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 VOUT and GND.
Likewise, with the output capacitor, there is no spe-
cific capacitor ESR requirement. If desired, COUT
may be increased without limit to accommodate
any load transient condition without adversely
affecting the slew rate.
Enable Function
The AAT4252A features an enable / disable func-
tion. This pin (ON) is active high and is compatible
with TTL or CMOS logic. To assure the load switch
will turn on, the ON control level must be greater
than 2.0V. The load switch will go into shutdown
mode when the voltage on the ON pin falls below
0.8V. When the load switch is in shutdown mode,
the OUT pin is tri-stated, and quiescent current
drops to leakage levels below 1μA.
Reverse Output-to-Input Voltage
Conditions and Protection
Under normal operating conditions, a parasitic
diode exists between the output and input of the
load switch. The input voltage should always remain
greater than the output load voltage, maintaining a
reverse bias on the internal parasitic diode.
Conditions where VOUT might exceed VIN should be
avoided since this would forward bias the internal
parasitic diode and allow excessive current flow into
9

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