AAT4282B Datasheet, PDF (9/13 Pages) Skyworks Solutions Inc. – Slew Rate Controlled Load Switch

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 VIN pin as prac-
tically possible. Ceramic, tantalum, or aluminum electro-
lytic capacitors may be selected for C_IN. There is no
specific capacitor equivalent series resistance (ESR)
requirement for C_IN. However, for higher current opera-
tion, ceramic capacitors are recommended for C_IN 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, C_OUT may be increased without
limit to accommodate any load transient condition with-
out adversely affecting the slew rate.
Enable Function
The AAT4282B features an enable / disable function. This
pin (ENx) is active high and is compatible with TTL or
CMOS logic. To assure the load switch will turn on, the
signal level must be greater than 1.4V. The load switch
will go into shutdown mode when the voltage on the ENx
pin falls below 0.4V. When the load switch is in shutdown
mode, the OUT pin is tri-stated, and the quiescent cur-
rent 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 V_OUT might
exceed V_IN should be avoided since this would forward
DATA SHEET
AAT4282B
Slew Rate Controlled Load Switch
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 V_OUT
exceeding V_IN for brief periods of time during normal
operation, the use of a larger value C_IN capacitor is
highly recommended. A larger value of C_IN with respect
to C_OUT will effect a slower C_IN decay rate during shut-
down, thus preventing V_OUT from exceeding V_IN. In appli-
cations where there is a greater danger of V_OUT exceeding
V_IN for extended periods of time, it is recommended to
place a Schottky diode from V_IN to V_OUT (connecting the
cathode to V_IN and anode to V_OUT). The Schottky diode
forward voltage should be less than 0.45V.
Thermal Considerations and
High Output Current Applications
The AAT4282B 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 minimum
recommended footprint as stated in the Printed Circuit
Board Layout Recommendations section of this data-
sheet.
At any given ambient temperature (T_A), the maximum
package power dissipation can be determined by the fol-
lowing equation:
P_D(MAX) =
T_J(MAX) -
θ_JA
T_A
Constants for the AAT4282B are maximum junction tem-
perature (T_J(MAX) = 125°C)¹ and package thermal resis-
tance (_JA = 74°C/W). Worst case conditions are calcu-
lated at the maximum operating temperature, T_A =
85°C. Typical conditions are calculated under normal
ambient conditions where T_A = 25°C. At T_A = 85°C,
P_D(MAX) = 541mW. At T_A = 25°C, P_D(MAX) = 1351mW.
The maximum continuous output current for the
AAT4282B is a function of the package power dissipation
and the R_DS of the MOSFET at T_J(MAX). The maximum R_DS
of the MOSFET at T_J(MAX) is calculated by increasing the
1. The actual maximum junction temperature of AAT4282B 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.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
201859B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 14, 2012
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