AAT4250_06 ANALOGICTECH [Advanced Analogic Technologies], AAT4250_06 Datasheet - Page 9

• Manufacturer Part Number: AAT4250_06
• Description: Slew Rate Controlled Load Switch
• Manufacturer: ANALOGICTECH [Advanced Analogic Technologies]

Enable Function
The AAT4250 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
2.0V. The load switch will go into shutdown mode
when the voltage on the ON pin falls below 0.8V.
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 V
avoided since this would forward bias the internal
parasitic diode and allow excessive current flow into
the V
In applications where there is a possibility of V
exceeding V
mal operation, the use of a larger value C
tor 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 V
cathode to V
diode forward voltage should be less than 0.45V.
Thermal Considerations and High
Output Current Applications
The AAT4250 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 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 datasheet.
4250.2006.03.1.3
OUT
pin, possibly damaging the load switch.
IN
IN
IN
. In applications where there is a
for brief periods of time during nor-
and anode to V
OUT
OUT
OUT
will effect a slower C
might exceed V
IN
exceeding V
to V
OUT
OUT
). The Schottky
(connecting the
IN
for extended
IN
should be
IN
OUT
IN
capaci-
decay
from
OUT
IN
Slew Rate Controlled Load Switch
At any given ambient temperature (T
mum package power dissipation can be deter-
mined by the following equation:
Constants for the AAT4250 are maximum junction
temperature (T
mal resistance (Θ
ditions are calculated at the maximum operating
temperature, T
culated under normal ambient conditions where T
= 25°C. At T
25°C, P
The maximum continuous output current for the
AAT4250 is a function of the package power dissi-
pation and the R
maximum R
lated by increasing the maximum room tempera-
ture R
temperature coefficient (TC) is 2800ppm/°C.
Therefore, at 125°C:
R
R
R
For maximum current, refer to the following equation:
For example, if V
= 25°C, I
were to exceed 1.7A 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
AAT4250. 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.
DS(MAX)
DS(MAX)
DS(MAX)
DS
D(MAX)
= R
= 175mΩ × (1 + 0.002800 × (125°C - 25°C))
= 224mΩ
OUT(MAX)
by the R
DS(25°C)
DS
I
A
OUT(MAX)
= 667mW.
A
J(MAX)
of the MOSFET at T
= 85°C, P
P
= 85°C. Typical conditions are cal-
DS
IN
D(MAX)
= 1.7A. If the output load current
JA
DS
× (1 + TC × ∆T)
= 5V, R
of the MOSFET at T
= 150°C/W). Worst case con-
<
temperature coefficient. The
= 125°C) and package ther-
=
⎛
⎝
P
T
D(MAX)
D(MAX)
R
J(MAX)
DS(MAX)
DS
θ
JA
⎞
⎠
- T
1
2
= 267mW. At T
AAT4250
= 224mΩ, and T
A
J(MAX)
A
), the maxi-
J(MAX)
is calcu-
. The
A
9
=
A
A