AAT4285 Analogic Corporation, AAT4285 Datasheet - Page 8

• Manufacturer Part Number: AAT4285
• Description: 12V Slew Rate Controller Load Switch
• Manufacturer: Analogic Corporation

Applications Information
Input Capacitor
A 1µF or larger capacitor is typically recommended
for C
required for basic operation. However, C
in preventing load transients from affecting
upstream circuits. C
the device V
Ceramic, tantalum, or aluminum electrolytic capac-
itors may be selected for C
capacitor ESR requirement for C
higher current operation, ceramic capacitors are
recommended for C
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 OUT and GND is recommended.
The output capacitor has no specific capacitor type
or ESR requirement. If desired, C
increased without limit to accommodate any load
transient condition without adversely affecting the
device turn-on slew rate time.
Enable Function
The AAT4285 features an enable / disable function.
This pin (ON/OFF) is compatible with both TTL and
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, maintaining a
reverse bias on the internal parasitic diode.
Conditions where V
avoided since this would forward bias the internal
parasitic diode and allow excessive current flow into
the OUT pin and possibly damage the load switch.
In applications where there is a possibility of V
exceeding V
mal operation, the use of a larger value C
8
IN
in most applications. A C
IN
IN
pin as practically possible.
for brief periods of time during nor-
OUT
IN
IN
should be located as close to
due to their inherent capabil-
might exceed V
IN
. There is no specific
IN
IN
capacitor is not
. However, for
OUT
IN
IN
should be
IN
is useful
may be
capac-
OUT
12V Slew Rate Controlled Load Switch
itor is highly recommended. A larger value of C
with respect to C
rate during shutdown, thus preventing V
exceeding V
greater danger of V
periods of time, it is recommended to place a
Schottky diode from IN to OUT (connecting the
cathode to IN and anode to OUT). The Schottky
diode forward voltage should be less than 0.45V.
Thermal Considerations and High
Output Current Applications
The AAT4285 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 utilizing
the minimum recommended footprint, as stated in
the Layout Considerations section of this datasheet.
At any given ambient temperature (T
mum package power dissipation can be deter-
mined by the following equation:
Constants for the AAT4285 are maximum junction
temperature, T
resistance, θ
are calculated at the maximum operating tempera-
ture where T
lated under normal ambient conditions where T
25°C. At T
25°C, P
The maximum continuous output current for the
AAT4285 is a function of the package power dissipa-
tion and the R
imum R
increasing the maximum room temperature R
the R
coefficient (TCR
MAX R
MAX R
DS
DS
DS
DS
D(MAX)
125°C = R
125°C = 240mΩ · (1 + 0.0028 · (125°C - 25°C))
temperature coefficient. The temperature
of the MOSFET at T
A
A
JA
IN
DS
= 85°C, P
= 714mW.
= 85°C. Typical conditions are calcu-
= 307mΩ
. In applications where there is a
J(MAX)
P
= 140°C/W. Worst case conditions
RDS
of the MOSFET at T
OUT
D(MAX)
DS
) is 2800ppm/°C. Therefore,
25°C · (1 + TCR
OUT
= 125°C, and package thermal
will affect a slower C
=
exceeding V
D(MAX)
T
J(MAX)
θ
JA
J(MAX
= 286mW. At T
- T
AAT4285
RDS
A
) is calculated by
J(MAX)
IN
· ΔT)
A
4285.2007.04.1.0
for extended
), the maxi-
. The max-
OUT
IN
decay
DS
from
A
A
by
IN
=
=