AAT4252AITP-3-T1 AnalogicTech, AAT4252AITP-3-T1 Datasheet - Page 10

• Manufacturer Part Number: AAT4252AITP-3-T1
• Description: Dual Slew Rate Controlled Load Switch
• Manufacturer: AnalogicTech

1. The actual maximum junction temperature of AAT4252A is 150°C. However, good design practice is to derate the maximum die temperature down to 125°C to prevent the
highly recommended. A larger value of C
to C
down, thus preventing V
cations where there is a greater danger of V
V
place a Schottky diode from V
cathode to V
forward voltage should be less than 0.45V.
Thermal Considerations and
High Output Current Applications
The AAT4252A 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 (T
package power dissipation can be determined by the fol-
lowing equation:
Constants for the AAT4252A are maximum junction tem-
perature (T
tance (
lated at the maximum operating temperature, T
85°C. Typical conditions are calculated under normal
ambient conditions where T
P
The maximum continuous output current for the AAT4252A
is a function of the package power dissipation and the R
of the MOSFET at T
at T
temperature R
10
SmartSwitch
D(MAX)
IN
possibility of over temperature damage.
for extended periods of time, it is recommended to
J(MAX)
OUT
= 250mW. At T
will effect a slower C
JA
is calculated by increasing the maximum room
= 160°C/W). Worst case conditions are calcu-
J(MAX)
IN
DS
and anode to V
= 125°C
by the R
TM
J(MAX)
P
D(MAX)
A
. The maximum R
= 25°C, P
OUT
=
1
DS
) and package thermal resis-
from exceeding V
T
temperature coefficient. The
J(MAX)
A
IN
IN
θ
= 25°C. At T
OUT
decay rate during shut-
JA
to V
D(MAX)
- T
). The Schottky diode
A
OUT
A
= 625mW.
), the maximum
DS
(connecting the
IN
of the MOSFET
OUT
with respect
IN
A
exceeding
w w w . a n a l o g i c t e c h . c o m
. In appli-
= 85°C,
A
DS
=
temperature coefficient (T
125°C:
R
R
R
For maximum current, refer to the following equation:
For example, if V
25°C, I
exceed 1.8A or if the ambient temperature were to
increase, the internal die temperature would increase
and the device would be damaged. Higher peak currents
can be obtained with the AAT4252A. To accomplish this,
the device thermal resistance must be reduced by
increasing the heat sink area or by operating the load
switch in a duty cycle manner. Duty cycles with peaks
less than 2ms in duration can be considered using the
method below.
High Peak Output Current Applications
Some applications require the load switch to operate at
a continuous nominal current level with short duration,
high-current peaks. Refer to the I
Absolute Maximum Ratings table to ensure the AAT4252A’s
maximum pulsed current rating is not exceeded. The
duty cycle for both output current levels must be taken
into account. To do so, first calculate the power dissipa-
tion at the nominal continuous current level, and then
add the additional power dissipation due to the short
duration, high-current peak scaled by the duty factor.
For example, a 4V system using an AAT4252A operates
at a continuous 100mA load current level and has short
2A current peaks, as in a GSM application. The current
peak occurs for 576μs out of a 4.61ms period.
First, the current duty cycle is calculated:
DS(MAX)
DS(MAX)
DS(MAX)
Dual Slew Rate Controlled Load Switch
% Peak Duty Cycle =
% Peak Duty Cycle =
OUT(MAX)
= R
= 155mΩ · (1 + 0.002800 · (125°C - 25°C))
= 198mΩ
DS(25°C)
= 1.8A. If the output load current were to
· (1 + T
IN
I
OUT(MAX)
= 5V, R
PRODUCT DATASHEET
AAT4252A
C
C
) is 2800ppm/°C. Therefore, at
<
⎛
⎝
12.5%
· ΔT)
100
x
DS(MAX)
⎞
⎠ =
P
R
D(MAX)
DS
DM
⎛
⎝
= 198mΩ, and T
4.61ms
576μs
specification in the
4252A.2009.06.1.1
⎞
⎠
A
=