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AAT4280A Datasheet, PDF (10/14 Pages) Advanced Analogic Technologies – Slew Rate Controlled Load Switch
AAT4280A
Slew Rate Controlled Load Switch
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, CIN 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 capac-
itors may be selected for CIN. There is no specific
capacitor ESR requirement for CIN; however, for
higher current operation, ceramic capacitors are
recommended for CIN due to their inherent capabil-
ity over tantalum capacitors to withstand input cur-
rent surges from low impedance sources, such as
batteries in portable devices.
Output Capacitor
For proper slew operation, a 0.1µF capacitor or
greater between VOUT and GND is recommended.
The output capacitor has no specific capacitor type
or ESR requirement. If desired, COUT may be
increased without limit to accommodate any load
transient condition without adversely affecting the
device turn-on slew rate time.
Enable Function
The AAT4280A features an enable / disable func-
tion. This pin (ON/OFF) is compatible with both
TTL or CMOS logic.
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, main-
taining 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 the VOUT pin and possibly damage
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 shutdown, thus preventing VOUT from
exceeding VIN. In applications 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 AAT4280A is designed to deliver a continuous
output load current. The limiting characteristic for
maximum safe operating output load current is
package power dissipation. In order to obtain high
operating currents, careful device layout and circuit
operating conditions need to be taken into account.
The following discussions will assume the load
switch is mounted on a printed circuit board utiliz-
ing the minimum recommended footprint, as stated
in the Layout Considerations section of this
datasheet.
At any given ambient temperature (TA), the maxi-
mum package power dissipation can be deter-
mined by the following equation:
PD(MAX)
=
[TJ(MAX) -
θJA
TA]
Constants for the AAT4280A are maximum junction
temperature, TJ(MAX) = 125°C, and package thermal
resistance, ΘJA = 120°C/W. Worst case conditions
are calculated at the maximum operating tempera-
ture where TA = 85°C. Typical conditions are cal-
culated under normal ambient conditions where TA
= 25°C. At TA = 85°C, PD(MAX) = 333mW. At TA =
25°C, PD(MAX) = 833mW.
The maximum continuous output current for the
AAT4280A is a function of the package power dis-
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4280A.2005.11.1.3