SmartSwitch
TM
General Description
The AAT4250 SmartSwitchTM is a member of
AATI's Application Specific Power MOSFETTM
(ASPMTM) product family. It is a Slew Rate
Controlled P-channel MOSFET power switch
designed for high-side load-switching applications.
This switch operates with an input voltage range
from 1.8V to 5.5V, making it ideal for 2.5V, 3.3V or
5V systems. The part features 1.5ms turn on and
10s turn off time. The AAT4250 has an under volt-
age lock out which turns off the switch when an
under-voltage condition exists. Input logic levels
are TTL compatible. The quiescent supply current
is very low, typically 2A. In shutdown mode, the
supply current is typically reduced to 0.1A or less.
The AAT4250 is available in a 5-pin SOT23 and 8-
pin SC70JW specified over -40 to 85C.
Features
1.8V to 5.5V Input voltage range
120m
(5V) typical R
DS(ON)
Low quiescent current
Typical 2A
Typical 0.1A with Enable off
Only 2.0V needed for ON/OFF Control
Temperature range -40 to 85C
5kV ESD rating
5-pin SOT23 or SC70JW-8 package
Applications
Hot swap supplies
Notebook computers
Personal communication devices
AAT4250
Slew Rate Controlled Load Switch
Typical Application
AAT4250
SOT23
ON/OFF
IN
OUT
GND
ON
1
F
0.1
F
INPUT
GND
GND
C
IN
C
OUT
OUTPUT
Preliminary
Information
4250.2001.12.0.94
1
Pin Descriptions
Pin Configuration
SOT23-5
(Top View)
SC70JW-8
(Top View)
GND
GND
GND
1
2
IN
IN
ON/OFF
GND
OUT
1
2
3
4
8
7
6
5
1
2
3
NC
OUT
4
5
GND
IN
ON/OFF
Pin #
SOT23-5
SC70JW
Symbol
Function
1
1
OUT
P-channel MOSFET drain
2
2, 3, 4, 5
GND
Ground connection
3
n/a
NC
Not internally connected
4
6
ON/OFF
Active-High Enable Input (Logic high turns the switch on)
5
7, 8
IN
P-channel MOSFET source
AAT4250
Slew Rate Controlled Load Switch
2
4250.2001.12.0.94
Absolute Maximum Ratings
(T
A
=25C unless otherwise noted)
Note: Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at con-
ditions other than the operating conditions specified is not implied. Only one Absolute Maximum rating should be applied at any one time.
Note 1: Human body model is a 100pF capacitor discharged through a 1.5k
resistor into each pin.
Thermal Characteristics
Note 2: Mounted on an AAT4250 demo board in still 25C air.
Electrical Characteristics
(V
IN
= 5V, T
A
= -40 to 85C unless otherwise noted. Typical values
are at T
A
=25C)
Note 3: For V
IN
outside this range consult typical ON/OFF threshold curve.
Symbol
Description
Conditions
Min
Typ
Max
Units
V
IN
Operation Voltage
1.8
5.5
V
I
Q
Quiescent Current
V
IN
= 5V, ON/OFF = V
IN
, I
OUT
= 0
2
4
A
I
Q(OFF)
Off Supply Current
ON/OFF = GND, V
IN
= 5V, OUT open
1
A
I
SD(OFF)
Off Switch Current
ON/OFF = GND, V
IN
= 5V, V
OUT
= 0
0.1
1
A
V
UVLO
Undervoltage Lockout
V
IN
falling
1.5
V
V
UVLO(hys)
Undervoltage Lockout hysteresis
250
mV
V
IN
= 5V
120
175
m
R
DS(ON)
On-Resistance
V
IN
= 3V
135
200
m
V
IN
=1.8V
165
m
TC
RDS
On-Resistance Temp-Co
2800
ppm/C
V
IL
ON/OFF Input Logic Low Voltage
V
IN
= 2.7V to 5.5V
3
0.8
V
V
IH
ON/OFF Input Logic High Voltage
V
IN
= 2.7V to
4.2V
2.0
V
V
IN
= > 4.2V to 5.5V
2.4
I
SINK
ON Input leakage
V
ON
= 5V
0.01
1
A
T
D
Output Turn-On Delay Time
300
s
T
OFF
Turn-Off Fall Time
V
IN
=5V, R
LOAD
=10
10
s
T
OFF
Turn-Off Fall Time
V
IN
=3V, R
LOAD
=5
10
s
T
ON
Turn-On Rise Time
V
IN
=5V, R
LOAD
=16.5
, T
A
=0 to 50 C
1000
s
T
ON
Turn-On Rise Time
V
IN
=5V, R
LOAD
=10
, C
OUT
=0.1F
1500
s
T
ON
Turn-On Rise Time
V
IN
=3V, R
LOAD
=5
, C
OUT
=0.1F
1500
s
Symbol
Description
Value
Units
JA
Thermal Resistance (SOT23-5 or SC70JW-8)
2
150
C/W
P
D
Power Dissipation (SOT23-5 or SC70JW-8)
2
667
mW
Symbol
Description
Value
Units
V
IN
IN to GND
-0.3 to 6
V
V
ON
ON/OFF to GND
-0.3 to 6
V
V
OUT
OUT to GND
-0.3 to V
IN
+0.3
V
I
MAX
Maximum Continuous Switch Current
1.7
A
I
DM
Maximum Pulsed Current
IN
2.5V
4
A
IN < 2.5V
2
A
T
J
Operating Junction Temperature Range
-40 to 150
C
T
LEAD
Maximum Soldering Temperature (at Leads)
300
C
V
ESD
ESD Rating
1
- HBM
5000
V
AAT4250
Slew Rate Controlled Load Switch
4250.2001.12.0.94
3
Typical Characteristics
(Unless otherwise noted, V
IN
= 5V, T
A
= 25C)
Turn-On Time vs. Temperature
0.5
1.0
1.5
2.0
2.5
3.0
-40
-20
0
20
40
60
80
100
Temperature (
C)
Turn-ON Time (ms)
C
IN
=1
F, C
OUT
=0.1
F
V
IN
=5V
R
LOAD
=10
V
IN
=3V
R
LOAD
=5
Turn-OFF Time vs. Temperature
5
6
7
8
9
10
-40
-20
0
20
40
60
80
100
Temperature (
C)
C
IN
=1
F, C
OUT
=0.1
F
Turn-OFF Time (
s)
V
IN
=5V
R
LOAD
=10
V
IN
=3V
R
LOAD
=5
Off-Switch Current vs. Temperature
1
10
100
1000
10000
-40
-20
0
20
40
60
80
100
Temperature (
C)
Off-Switch Current (nA)
Off-Supply Current vs. Temperature
1
10
100
1000
-40
-20
0
20
40
60
80
100
Temperature (
C)
Off-Supply Current (nA)
Quiescent Current vs. V
IN
0
0.5
1
1.5
2
2.5
3
3.5
4
0
1
2
3
4
5
6
Quiescent Current (
A)
V
IN
Quiescent Current vs. Temperature
0
0.5
1
1.5
2
2.5
3
3.5
4
-40
-20
0
20
40
60
80
100
Temperature (
C)
Quiescent Current (
A)
V
IN
=3V
V
IN
=5V
AAT4250
Slew Rate Controlled Load Switch
4
4250.2001.12.0.94
(Unless otherwise noted, V
IN
= 5V, T
A
= 25C)
1
3
5
C
IN
=1
F,C
OUT
=1
F,V
IN
=5V
Turn Off Waveforms
Time (
s)
-1
-1
1
3
5
7
9
11
13
15
V(out)
Volt
V(ON/OFF)
0
1
2
3
4
C
IN
=1
F,C
OUT
=1
F,V
IN
=3V
Turn Off Waveforms
Time (
s)
-1
-1
1
3
5
7
9
11
13
15
V(out)
Volt
V(ON/OFF)
-1
0
1
2
3
4
0
1
1.2
Time (ms)
C
IN
=1
F,C
OUT
=10
F,V
IN
=5V
Turn On Waveforms
V(out)
0.8
0.6
0.4
0.2
5
6
I(in)
Volt
4
3
2
1
0
A
V(ON/OFF)
Volt
-1
0
1
2
3
4
0
1
2
3
4
0
0.5
1
1.5
2
Time (ms)
C
IN
=1
F,C
OUT
=10
F,V
IN
=3V
Turn On Waveforms
V(out)
I(in)
A
V(ON/OFF)
Vo
lt
-1
0
1
2
3
4
0
1
2
3
4
0
1
1.2
Time (ms)
C
IN
=1
F,C
OUT
=0.1
F,V
IN
=5V
Turn On Waveforms
V(out)
0.8
0.6
0.4
0.2
5
6
I(in)
A
V(ON/OFF)
Volt
-1
0
1
2
3
4
0
1
2
3
4
0
0.5
1
1.5
2
Time (ms)
C
IN
=1
F,C
OUT
=0.1
F,V
IN
=3V
Turn On Waveforms
V(ON/OFF)
V(out)
I(in)
A
AAT4250
Slew Rate Controlled Load Switch
4250.2001.12.0.94
5
(Unless otherwise noted, V
IN
= 5V, T
A
= 25C)
Typical ON/OFF Threshold vs. V
IN
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
V
IN
ON/OFF Threshold
V
IH
V
IL
R
DS(ON)
vs. V
IN
110
120
130
140
150
160
170
180
190
1.5
2
2.5
3
3.5
4
4.5
5
5.5
V
IN
R
DS(ON)
(m
)
I
OUT
= 100mA
R
DS(ON)
vs. Temperature
80
120
160
-40
-20
0
20
40
60
80
100
Temperature (
C)
R
DS(ON)
(m
)
V
IN
=3V
V
IN
=5V
AAT4250
Slew Rate Controlled Load Switch
6
4250.2001.12.0.94
Functional Description
The AAT4250 is a slew rate controlled P-channel
MOSFET power switch designed for high-side load-
switching applications. It operates with input volt-
ages ranging from 1.8V to 5.5V which, along with its
extremely low operating current, makes it ideal for
battery-powered applications. In cases where the
input voltage drops below 1.8V, the AAT4250 MOS-
FET is protected from entering the saturated region
of operation by automatically shutting down. In
addition, the TTL compatible ON/OFF pin makes
the AAT4250 an ideal level shifted load-switch. The
slew rate controlling feature eliminates in-rush cur-
rent when the MOSFET is turned on, allowing the
AAT4250 to be implemented with a small input
capacitor, or no input capacitor at all. During slew-
ing, the current ramps linearly until it reaches the
level required for the output load condition. The
proprietary control method works by careful control
and monitoring of the MOSFET gate voltage. When
the device is switched ON, the gate voltage is quick-
ly increased to the threshold level of the MOSFET.
Once at this level, the current begins to slew as the
gate voltage is slowly increased until the MOSFET
becomes fully enhanced. Once it has reached this
point, the gate is quickly increased to the full input
voltage and R
DS(ON)
is minimized.
AAT4250
Slew Rate Controlled Load Switch
4250.2001.12.0.94
7
Functional Block Diagram
Under-
voltage
Lockout
Level
Shift
Slew Rate
Control
IN
ON/OFF
GND
OUT
Applications Information
Input Capacitor
Typically a 1F or larger capacitor is recommend-
ed for C
IN
in most applications. A C
IN
capacitor is
not required for basic operation, however, it is use-
ful in preventing load transients from affecting up
stream circuits. C
IN
should be located as close to
the device V
IN
pin as practically possible. Ceramic,
tantalum or aluminum electrolytic capacitors may
be selected for C
IN
. There is no specific capacitor
ESR requirement for C
IN
. However, for higher cur-
rent operation, ceramic capacitors are recom-
mended for C
IN
due to their inherent capability over
tantalum capacitors to withstand input current
surges from low impedance sources such as bat-
teries in portable devices.
Output Capacitor
For proper slew operation, a 0.1F capacitor or
greater between VOUT and GND is required.
Likewise, with the output capacitor, there is no spe-
cific capacitor ESR requirement. If desired, C
OUT
maybe increased without limit to accommodate any
load transient condition without adversely affecting
the slew rate.
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
2.0 volts. The load switch will go into shutdown
mode when the voltage on the ON pin falls below
0.8 volts. When the load switch is in shutdown
mode, the OUT pin is tristated, and quiescent cur-
rent drops to leakage levels below 1A.
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 V
OUT
might exceed V
IN
should be avoided since this would forward bias
the internal parasitic diode and allow excessive
current flow into the V
OUT
pin and possibly damage
the load switch.
In applications where there is a possibility of V
OUT
exceeding V
IN
for brief periods of time during nor-
mal operation, the use of a larger value C
IN
capaci-
tor is highly recommended. A larger value of C
IN
with respect to C
OUT
will effect a slower C
IN
decay
rate during shutdown, thus preventing V
OUT
from
exceeding V
IN
. In applications where there is a
greater danger of V
OUT
exceeding V
IN
for extended
periods of time, it is recommended to place a schot-
tky diode from V
IN
to V
OUT
(connecting the cathode
to V
IN
and anode to V
OUT
). The Schottky diode for-
ward voltage should be less then 0.45 volts.
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 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.
At any given ambient temperature (T
A
) the maxi-
mum package power dissipation can be deter-
mined by the following equation:
P
D(MAX)
= [T
J(MAX)
- T
A
] /
JA
Constants for the AAT4250 are maximum junction
temperature, T
J(MAX)
= 125C, and package thermal
resistance,
JA
= 150C/W. Worst case conditions
are calculated at the maximum operating tempera-
ture where T
A
= 85C. Typical conditions are cal-
culated under normal ambient conditions where T
A
= 25C. At T
A
= 85C, P
D(MAX)
= 267mW. At T
A
=
25C, P
D(MAX)
= 667mW.
The maximum continuous output current for the
AAT4250 is a function of the package power dissi-
pation and the R
DS
of the MOSFET at T
J(MAX)
. The
maximum R
DS
of the MOSFET at T
J(MAX)
is calcu-
lated by increasing the maximum room tempera-
ture R
DS
by the R
DS
temperature coefficient. The
temperature coefficient (TC) is 2800ppm/C.
Therefore, at 125C
R
DS(MAX)
= R
DS(25C)
(1 + TC T)
R
DS(MAX)
= 175m
(1 + .002800 (125C - 25C))
R
DS(MAX)
= 224m
AAT4250
Slew Rate Controlled Load Switch
8
4250.2001.12.0.94
For maximum current, refer to the following equation:
I
OUT(MAX)
< ( P
D(MAX)
/ R
DS
)
1/2
For example, if V
IN
= 5V, R
DS(MAX)
=224m
and T
A
= 25C, I
OUT(MAX)
= 1.7A. If the output load current
were to exceed 1.7A or if the ambient temperature
were to increase, the internal die temperature will
increase, and the device will 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.
High Peak Output Current Applications
Some applications require the load switch to oper-
ate at a continuous nominal current level with short
duration high current peaks. Refer to the I
DM
spec-
ification in the Absolute Maximum table to ensure
the AAT 4250's maximum pulsed current rating is
not exceeded. The duty cycle for both output cur-
rent levels must be taken into account. To do so,
first calculate the power dissipation at the nominal
continuous current level, and then add in the addi-
tional power dissipation due to the short duration
high current peak scaled by the duty factor.
For example, a 4V system using an AAT4250 oper-
ates at a continuous 100mA load current level and
has short 2A current peaks, as in a GSM applica-
tion. The current peak occurs for 576s out of a
4.61ms period.
First, the current duty cycle is calculated:
% Peak Duty Cycle: X/100 = 576s/4.61ms
% Peak Duty Cycle = 12.5%
The load current is 100mA for 87.5% of the 4.61ms
period and 2A for 12.5% of the period. Since the
Electrical Characteristics do not report R
DS MAX
for 4
volts operation, it must be calculated approximated
by consulting the chart of R
DSON
vs. V
IN
. The Rds
reported for 5 volt R
DS
can be scaled by the ratio
seen in the chart to derive the Rds for 4 volt V
IN
:
175m
x 120m/115m = 183m. Derated for
temperature: 183m
x (1 + .002800 x (125C -
25C)) = 235m
. The power dissipation for a
100mA load is calculated as follows:
P
D(MAX)
= I
2
OUT
x R
DS
P
D(100mA)
= (100mA)
2
x 235m
P
D(100mA)
= 2.35mW
P
D(87.5%D/C)
= %DC x P
D(100mA)
P
D(87.5%D/C)
= 0.875 x 2.35mW
P
D(87.5%D/C)
= 2.1mW
The power dissipation for 100mA load at 87.5%
duty cycle is 2.1mW. Now the power dissipation for
the remaining 12.5% of the duty cycle at 2A is cal-
culated:
P
D(MAX)
= I
2
OUT
x R
DS
P
D(2A)
= (2A)
2
x 235m
P
D(2A)
= 940mW
P
D(12.5%D/C)
= %DC x P
D(2A)
P
D(12.5%D/C)
= 0.125 x 940mW
P
D(12.5%D/C)
= 117.5mW
The power dissipation for 2A load at 12.5% duty
cycle is 117mW. Finally, the two power figures are
summed to determine the total true power dissipa-
tion under the varied load.
P
D(total)
= P
D(100mA)
+ P
D(2A)
P
D(total)
= 2.1mW + 117.5mW
P
D(total)
= 120mW
The maximum power dissipation for the AAT4250
operating at an ambient temperature of 85C is
267mW. The device in this example will have a
total power dissipation of 120mW. This is well with
in the thermal limits for safe operation of the
device, in fact, at 85C, the AAT4250 will handle a
2A pulse for up to 28% duty cycle. At lower ambi-
ent temperatures the duty cycle can be further
increased.
AAT4250
Slew Rate Controlled Load Switch
4250.2001.12.0.94
9
AAT4250
Slew Rate Controlled Load Switch
10
4250.2001.12.0.94
Figure 1: Evaluation board
Figure 2: Evaluation board
Figure 3: Evaluation board
top side silk screen layout /
component side layout
solder side layout
assembly drawing
Printed Circuit Board Layout
Recommendations
For proper thermal management, and to take
advantage of the low R
DSON
of the AAT4250, a few
circuit board layout rules should be followed: Vin
and Vout should be routed using wider than normal
traces, and GND should be connected to a ground
plane. For best performance, C
IN
and C
OUT
should
be placed close to the package pins.
Evaluation Board Layout
The AAT4250 evaluation layout follows the printed
circuit board layout recommendations, and can be
used for good applications layout.
Note: Board layout shown is not to scale.
AAT4250
Slew Rate Controlled Load Switch
4250.2001.12.0.94
11
Ordering Information
Package Information
SOT23-5
E
A
c
b
D
e
S1
L
H
A2
S
Package
Marking
Part Number
Bulk
Tape and Reel
SOT23-5
N/A
AAT4250IGV-T1
SC70JW-8
N/A
AAT4250IJS-T1
Dim
Millimeters
Inches
Min
Max
Min
Max
A
1.00
1.30
0.039
0.051
A1
0.00
0.10
0.000
0.004
A2
0.70
0.90
0.028
0.035
b
0.35
0.50
0.014
0.020
c
0.10
0.25
0.004
0.010
D
2.70
3.10
0.106
0.122
E1.40
1.80
0.055
0.071
e
1.90
0.075
H
2.60
3.00
0.102
0.118
L
0.37
0.015
S
0.45
0.55
0.018
0.022
S1
0.85
1.05
0.033
0.041
1
9
1
9
SC70JW-8
1
D
A
A2
b
E
e
e
e
L
E1
A1
c
0.048REF
AAT4250
Slew Rate Controlled Load Switch
12
4250.2001.12.0.94
Advanced Analogic Technologies, Inc.
1250 Oakmead Parkway, Suite 310, Sunnyvale, CA 94086
Phone (408) 524-9684
Fax (408) 524-9689
Dim
Millimeters
Inches
Min
Max
Min
Max
E2.10 BSC
0.083 BSC
E1
1.75
2.00
0.069
0.079
L
0.23
0.40
0.009
0.016
A
1.10
0.043
A1
0
0.10
0.004
A2
0.70
1.00
0.028
0.039
D
2.00 BSC
0.079 BSC
e
0.50 BSC
0.020 BSC
b
0.15
0.30
0.006
0.012
c
0.10
0.20
0.004
0.008
0
8
0
8
1
4
10
4
10
PDF 
ZIP