AAT4250 Просмотр технического описания (PDF) - Advanced Analogic Technologies

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AAT4250

Slew Rate Controlled Load Switch

Advanced Analogic Technologies 

Functional Block Diagram

AAT4250

Slew Rate Controlled Load Switch

IN

ON/OFF

OUT

Under-

Voltage

Lockout

Slew Rate

Control

Level

Shift

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

RDS(ON) is minimized.

8

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 operation, ceram-

ic 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.

4250.2006.03.1.3

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