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AAT4282A

Slew Rate Controlled Load Switch

Advanced Analogic Technologies 

SmartSwitchTM

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 prac-

tically possible. Ceramic, tantalum, or aluminum electro-

lytic capacitors may be selected for CIN. There is no

specific capacitor equivalent series resistance (ESR)

requirement for CIN. However, for higher current opera-

tion, ceramic capacitors are recommended for CIN due to

their inherent capability over tantalum capacitors to

withstand 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 specific capacitor ESR

requirement. If desired, COUT may be increased without

limit to accommodate any load transient condition with-

out adversely affecting the slew rate.

Enable Function

The AAT4282A features an enable / disable function. 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 1.4V. The load

switch will go into shutdown mode when the voltage on

the ON pin falls below 0.4V. 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

PRODUCT DATASHEET

AAT4282A

Slew Rate Controlled Load Switch

exceed VIN should be avoided since this would forward

bias the internal parasitic diode and allow excessive cur-

rent flow into the VOUT pin, possibly damaging the load

switch. In applications where there is a possibility of VOUT

exceeding VIN for brief periods of time during normal

operation, the use of a larger value CIN capacitor is

highly recommended. A larger value of CIN with respect

to COUT will effect a slower CIN decay rate during shut-

down, thus preventing VOUT from exceeding VIN. In appli-

cations where there is a greater danger of VOUT exceeding

VIN for extended periods of time, it is recommended to

place a Schottky diode from VIN to VOUT (connecting the

cathode to VIN and anode to VOUT). The Schottky diode

forward voltage should be less than 0.45V.

Thermal Considerations and

High Output Current Applications

The AAT4282A is designed to deliver a continuous output

load current. The limiting characteristic for maximum

safe operating output load current is package power dis-

sipation. In order to obtain high operating currents,

careful device layout and circuit operating conditions

must be taken into account.

The following discussions will assume the load switch is

mounted on a printed circuit board utilizing the mini-

mum recommended footprint as stated in the Printed

Circuit Board Layout Recommendations section of this

datasheet.

At any given ambient temperature (TA), the maximum

package power dissipation can be determined by the fol-

lowing equation:

PD(MAX) =

TJ(MAX) -

θJA

TA

Constants for the AAT4282A are maximum junction tem-

perature (TJ(MAX) = 125°C)1 and package thermal resis-

tance (θJA = 70°C/W). Worst case conditions are calcu-

lated at the maximum operating temperature, TA =

85°C. Typical conditions are calculated under normal

ambient conditions where TA = 25°C. At TA = 85°C,

PD(MAX) = 571mW. At TA = 25°C, PD(MAX) = 1429mW.

1. The actual maximum junction temperature of AAT4282A is 150°C. However, good design practice is to derate the maximum die temperature to 125°C to prevent the possibil-

ity of over-temperature damage.

4282A.2008.02.1.2

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