SmartSwitch

General Description

The AAT4650 SmartSwitchTM is a single channel PC
Card (PCMCIA) power switch. It is used to select
between two different voltage inputs, each between
2.7V and 5.5V. An internal switch powers the cir-
cuitry from whichever input voltage is higher. The
device's output, V

, is slew rate controlled and cur-

rent limited, in compliance with PC Card specifica-
tions. The current limit response time to a short cir-
cuit is typically 1µs. The internal P-Channel MOS-
FET switches are configured to break before make,
that is, both switches cannot be closed at the same
time. Controlled by a 2 bit parallel interface, the four
states for V

are V

5, V

3, Hi-impedance, or

Ground. When in the ground state, V

is pulled to

ground by a 5k

resistor. An open drain FAULT out-

put is asserted during over-current conditions.
During power up slewing, FAULT also signals that
V

is out of tolerance. An internal over temperature

sensor forces V

to a high impedance state when

an over-temperature condition exists. Quiescent
current is typically a low 15µA, as long as I

is less

than approximately 500mA. Above this load current,
the quiescent current increases to 200µA.

The AAT4650 is available in 8-pin SOP and
TSSOP packages specified over -40 to 85°C.

Features

2.7V to 5.5V Input voltage range

85m

(5V) typical R

DS(ON)

Low quiescent current 15µA (typ)

Reverse-blocking switches

Short-circuit protection

Over-temperature protection

FAULT flag output

Temp range -40 to 85°C

8 pin SOP or TSSOP package

Applications

Notebook Computer

PDA, Subnotebook

Power Supply Multiplexer Circuit

AAT4650

5V/3V PC Card Power Switch

Typical Application

OUT

0.1

IN5

IN3

CTL1
CTL0

FAULT

GND

AAT4650

6,7

GND

CTL1
CTL0

FAULT

Preliminary

Information

4650.2001.10.0.93

Absolute Maximum Ratings

=25°C 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 FR4 board.

Electrical Characteristics

= 5V, T

= -40 to 85°C unless otherwise noted. Typical values

are at T

=25°C; bold values designate full temperature range)

Symbol

Description

Conditions

Min

Typ

Max

Units

Output

Hi-Z

High impedance Output

OFF mode, V

=0V

µA

Leakage Current

Iccsc

Short Circuit Current Limit

CCIN

-0.5V, ON mode V

1.0

2.0

or V

5 selected, T

=25°C

DS(ON)

On-Resistance

=3.0v, T

=25°C

110

=5.0v, T

=25°C

100

Tcrds

Switch Resistance Tempco

2800

ppm/ºC

Switching Time (Refer to Figure 1)

Output Turn-On Delay Time

=0v to 10% of 3.3V, R

OUT

=10

500

2000

µs

Output Turn-On Delay Time

=0v to 10% of 5.0V, R

OUT

=10

500

1500

µs

Output Rise Time

=10% to 90% of 3.3V, R

LOAD

=10

300

1000 3000

µs

Output Rise Time

=10% to 90% of 5.0V, R

LOAD

=10

300

1000 3000

µs

Output Turn-Off Delay Time

=3.3 to 90% of 3.3V, R

LOAD

=10

400

µs

Output Turn-Off Delay Time

=5.0 to 90% of 5.0V, R

LOAD

=10

400

µs

Output Fall Time to OFF State

=90% to 10% of 3.3V, R

LOAD

=10

200

µs

Output Fall Time to OFF State

=90% to 10% of 5.0V, R

LOAD

=10

200

µs

Output Fall Time to Hi-Z State

=90% to 10% of 3.3V, R

LOAD

=10

1500

µs

t10

Output Fall Time to Hi-Z State

=90% to 10% of 5.0V, R

LOAD

=10

2000

µs

Symbol

Description

Value

Units

Thermal Resistance (SOP-8)

100

°C/W

Power Dissipation (SOP-8)

1.25

Symbol

Description

Value

Units

3, V

IN to GND

-0.3 to 6

OUT to GND

-0.3 to 6

MAX

Maximum Continuous Switch Current

Current Limited

Operating Junction Temperature Range

-40 to 150

°C

LEAD

Maximum Soldering Temperature (at Leads)

300

°C

ESD

ESD Rating

-- HBM

4000

AAT4650

5V/3V PC Card Power Switch

4650.2001.10.0.93

Timing Diagram

Figure 1: V

Switching Time Diagram

Refer to V

Switching Time specifications under the Electrical Characteristics section for definitions of t1

to t10.

CTL0,1

Vcc

t3, t4

t1, t2

t5, t6

t7, t8

t9, t10

Symbol

Description

Conditions

Min

Typ

Max

Units

Power Supply

3 Operation Voltage

2.7

5.5

5 Operation Voltage

2.7

5.5

=5V or HiZ or OFF,

µA

3 Supply Current

3<V

5, I

Out=0

=3.3v, V

3<V

5, I

Out=0

µA

5 Supply Current

=Off, V

5>V

3, I

Out=0

µA

=HiZ, V

5>V

3, I

Out=0

µA

=3.3v, V

5>V

3 ,I

Out=0

µA

=5v, V

5>V

3, I

Out=0

µA

Parallel Interface

CTLLOW

CTL Input Low Voltage

0.8

CTLHI

CTL Input High Voltage

3 or V

5=2.7 to 3.6V

2.0

3 or V

5=4.5 to 5.5V

2.4

SINKCTL

CTL Input leakage

CTL

= 5.5V

0.01

µA

FAULTLOW

FAULT Logic Output Low

SINK

=1mA

0.4

Voltage

SINKFAULT

FAULT Logic Output High

FAULT

= 5.5V

0.05

µA

Leakage Current

Other

OTMP

Over Temperature Shutdown

125

degC

AAT4650

5V/3V PC Card Power Switch

4650.2001.10.0.93

Typical Characteristics

(Unless otherwise noted, T

= 25°C)

Rdson vs. Temperature

60.0

70.0

80.0

90.0

100.0

110.0

120.0

-40

-20

100

120

Temperature (C)

3=3.0V

5=5.0V

Off-Switch Current vs. Temperature I

0.0000

0.0001

0.0010

0.0100

0.1000

1.0000

-40

-20

100

120

Temperature (C)

5=5V

3=3V

CTL1=0V
CTL0=0V

Off-Switch Current (

Off-Switch Current vs. Temperature (I

0.0000

0.0001

0.0010

0.0100

0.1000

1.0000

-40

-20

100

120

Temperature (C)

3=3V

5=5V

CTL1=0V
CTL0=0V

Off-Switch Current (

Current Limit V

0.5

1.5

Vout

=25C

Current Limit V

0.5

1.5

0. 5

1. 5

2. 5

Vout

=25C

Quiescent Current vs. Temperature

-40

-20

100

120

Temperature (C)

3=3V

5=5V

CTL0=5V
CTL1=0V

Quiescent Current (

AAT4650

5V/3V PC Card Power Switch

4650.2001.10.0.93

(Unless otherwise noted, T

= 25°C)

Short Circuit Through 0.6 Ohm

-2

Input and Output (V)

Output (A)

-3

Output Current

Input Voltage

Output Voltage

Time (

Short Circuit Through 0.3 Ohm

-2

Time

Output (A)

Input and Output (V)

(

-1

Output Current

Input Voltage

Output Voltage

Thermal Shutdown Response

100ms / div

CTL1 (5V/div)

FAULT (5V/div)

(1V/div)

VCC5

(500mA/div)

Turn-ON/OFF Response with 15

Ohm 1

F load

CTL0 (5V/div)

(2V/div)

VCC5

(200mA/div)

FAULT (5V/div)

500

s/div

Turn-ON/OFF Response with 10

Ohm 1

F load

CTL1 (5V/div)

(2V/div)

VCC3

(200mA/div)

FAULT (5V/div)

500

s/div

AAT4650

5V/3V PC Card Power Switch

4650.2001.10.0.93

Functional Description

The AAT4650 is a single channel power switch that
can be used in any application where dual power
supply multiplexing is required. Typical applications
for this include PC card applications not requiring a
12 volt power supply, or applications where power is
switched, for example, between 5 volts for operation
and 3.3 volts for standby mode. The AAT4650 oper-
ates with input voltages ranging from 2.7 to 5.5 volts
in any combination and automatically powers its
internal circuitry off of whichever input voltage is
higher. Two identical low R

P-channel MOSFETS

serve as the power multiplexing circuit with a com-
mon drain as the Vcc output and independent
sources as the two Vcc3 and Vcc5 inputs. A two bit
parallel interface determines the state of the multi-
plexer: Vcc=Vcc3, Vcc=Vcc5, Vcc with resistive pull
down to ground, or Vcc hi-impedance. When the
state is set to either of the two inputs, the multiplex-

ing circuit will slowly slew the V

output to the new

voltage level which protects the upstream power
supply from sudden load transients. When the
resistive pull down is chosen for V

, the V

output

is quickly discharged by the resistive pull down.
The AAT4650 always serves as an electronic fuse
by limiting the load current if it exceeds the current
limit threshold. During power up into a short, the
current will gradually increase until the current limit
is reached. During a sudden short circuit on the out-
put, the current limit will respond in 1 µs to isolate
and protect the upstream power supply from the
load short circuit. In most applications, because the
response time is so fast, a short circuit to V

will

not affect the upstream supply, so system function-
ality will not be affected. In the case of an over cur-
rent condition, an open drain FAULT flag output will
signal the event. The FAULT output is also active
during output voltage slew, and becomes inactive
once the output is within regulation.

AAT4650

5V/3V PC Card Power Switch

4650.2001.10.0.93

Functional Block Diagram

Body Ctl

CTL0

CTL1

FAULT

GND

Over

Temperature

Over

Current

Over

Current

Control

Logic

Slew
Rate

Applications Information

Input Capacitor

Typically a 1µF or larger capacitor is recommended
for C

. A C

capacitor is not required for basic

operation, however, it is useful in preventing load
transients from affecting up stream circuits. C

should be located as close to the device V

pin as

practically possible. Ceramic, tantalum or aluminum
electrolytic capacitors may be selected for C

There is no specific capacitor ESR requirement for
C

. However, for higher current operation, ceramic

capacitors are recommended for C

due to their

inherent capability over tantalum capacitors to with-
stand input current surges from low impedance
sources such as batteries in portable devices.

Output Capacitor

A 0.1µF or greater capacitor is generally required
between Vcc and GND. Likewise, with the output
capacitor, there is no specific capacitor ESR
requirement. If desired, C

OUT

may be increased to

accommodate any load transient condition.

Parallel Interface / Break Before Make

A two bit parallel interface determines the state of
the Vcc output. The logic levels are compatible with
CMOS or TTL logic. A logic low value must be less
than 0.8 volts, and a logic high value must be greater
than 2.4 volts. In cases where the interface pins rap-
idly change state directly from 3v to 5v (or vice
versa), internal break before make circuitry prevents
any back flow of current from one input power sup-
ply to the other. In addition, the body connections of
the internal P-channel MOSFET switches are
always set to the highest potential of Vcc3, Vcc5, or
Vcc, which prevents any body diode conduction,
power supply backflow, or possible device damage.

FAULT Output

The FAULT output is pulled to ground by an open
drain N-channel MOSFET during an over current or
output slew condition. It should be pulled up to the
reference power supply of the controller IC via a
nominal 100K

resistor.

Voltage Regulation

The PC Card Specification calls for a regulated 5
volt supply tolerance of +/-5%. Of this, a typical
power supply will drop less than 2%, and the PCB
traces will drop another 1%. This leaves 2% for the
AAT4650 as the PC card switch. In the PC card
application, the maximum allowable current for the

AAT4650 is dominated by voltage regulation rather
than by thermal considerations, and is set by either
the current limit or the maximum R

of the P-chan-

nel MOSFET. The maximum R

at 85°C is calcu-

lated by applying the R

Tempco to the maximum

room temperature R

DS(MAX)

= R

DS25

x (1 + TC x

T), or

DS(MAX)

= 105m

x (1 + 0.0028 x 60) = 122m

The maximum current is equal to the 2% tolerance
of the 5 volt supply (100mV) across the AAT4650
divided by R

DS(MAX)

. Or

MAX5

= 100mV / 122m

= 820mA

For the 3.3 volt supply in the PC card application,
the conditions are a bit relaxed, with the allowable
voltage regulation drop equal to 300mV. With a 2%
supply, and 1% PCB trace regulation, the PC card
switch can have a 200mV drop. So

MAX3

= 200mV / 134m

= 1.5A

Since 1.5A is the nominal current limit value, the
AAT4650 will current limit before I

MAX3

is reached.

Thermal issues are not a problem in the SO-8 pack-
age since

, the package thermal resistance, is

only 120°C/W. At any given ambient temperature
(T

) the maximum package power dissipation can

be determined by the following equation:

D(MAX)

= [T

J(MAX)

- T

] /

Constants for the AAT4650 are maximum junction
temperature, T

J(MAX)

= 125°C, and package thermal

resistance,

= 120°C/W. Worst case conditions

are calculated at the maximum operating tempera-
ture where T

= 85°C. Typical conditions are cal-

culated under normal ambient conditions where T

= 25°C. At T

= 85°C, P

D(MAX)

= 333mW. At T

25°C, P

D(MAX)

= 833mW.

Maximum current is given by the following equation:

OUT(MAX)

= (P

D(MAX)

/ R

)

1/2

For the AAT4650 at 85°C, I

OUT(MAX)

= 1.65A, a

value greater than the internal minimum

current

limit specification.

Overcurrent and Overtemperature
Protection

Because many AAT4650 applications provide power
to external devices, it is designed to protect its host
device from malfunctions in those peripherals

AAT4650

5V/3V PC Card Power Switch

4650.2001.10.0.93

through slew rate control, current limiting, and ther-
mal limiting. The AAT4650 current limit and thermal
limit serve as an immediate and reliable electronic
fuse without any increase in R

for this function.

Other solutions such as a poly fuse do not protect
the host power supply and system from mishandling,
or short circuited peripherals, they will only prevent a
fire. The AAT4650 high speed current limit and
thermal limit not only prevent fires, they also isolate
the power supply and entire system from any activi-
ty at the external port, and report a mishap by means
of a FAULT signal.

Overcurrent and overtemperature go hand in hand.
Once an overcurrent condition exists, the current
supplied to the load by the AAT4650 is limited to the
overcurrent threshold. This results in a voltage drop
across the AAT4650 which causes excess power
dissipation and a package temperature increase. As
the die begins to heat up, the overtemperature circuit
is activated. If the temperature reaches the maxi-
mum level, the AAT4650 automatically switches off
the P-channel MOSFETs. While they are off, the
overtemperature circuit remains active. Once the
temperature has cooled by approximately 10°C, the
P-channel MOSFETs are switched back on. In this
manner, the AAT4650 is thermally cycled on and off
until the short circuit is removed. Once the short is
removed, normal operation automatically resumes.

To save power, the full high speed overcurrent cir-
cuit is not activated until a lower threshold of cur-
rent (approximately 700mA) is exceeded in the
power device. When the load current exceeds this

crude threshold, the AAT4650 quiescent current
increases from 15µA to 150µA. The high speed
overcurrent circuit works by linearly limiting the cur-
rent when the current limit is reached. As the volt-
age begins to drop on Vcc due to current limiting,
the current limit magnitude varies, and generally
decreases as the Vcc voltage drops to 0 volts.

Switching Vcc Voltage

The AAT4650 meets PC card standards for switch-
ing the Vcc output by providing a ground path for
Vcc as well as a hi impedance state. The PC card
protocol for determining low voltage operations is
to first power the peripheral with 5 volts and poll for
3.3 volt operation. When transitioning from 5 volts
to 3.3 volts, Vcc must be discharged to less than
0.8 volts to provide a hard reset. The resistive
ground state (CTL1=0, CTL0=0) will accommodate
this. The ground state will also guarantee the Vcc
voltage to be discharged within the specified
100ms amount of time.

Printed Circuit Board Layout
Recommendations

For proper thermal management, to minimize PCB
trace resistance, and to take advantage of the low
R

DS(ON)

of the AAT4650, a few circuit board layout

rules should be followed: Vcc3, Vcc5, and Vcc
should be routed using wider than normal traces, the
two Vcc pins (6 and 7) should be connected to the
same wide PCB trace, and GND should be connect-
ed to a ground plane. For best performance, C

and

OUT

should be placed close to the package pins.

AAT4650

5V/3V PC Card Power Switch

4650.2001.10.0.93

Typical PC Card Application Circuit

CTL1

CTL0

FAULT

GND

AAT4650

6,7

Power

Supply

3.3V

PC Card

Controller

PC Card

Slot

CTL1
CTL0

FAULT

100K

IN3

IN5

OUT

0.1

Ordering Information

Package Information

SOP-8

7 (4x)

Package

Marking

Part Number

Bulk

Tape and Reel

SO-8

AAT4650IAS-B1

AAT4650IAS-T1

TSSOP-8

AAT4650IHS-B1

AAT4650IHS-T1

AAT4650

5V/3V PC Card Power Switch

4650.2001.10.0.93

Dim

Millimeters

Inches

Min

Max

Min

Max

1.35

1.75

0.053

0.069

0.10

0.25

0.004

0.010

1.45

0.057

0.33

0.51

0.013

0.020

0.19

0.25

0.007

0.010

4.80

5.00

0.189

0.197

3.80

4.00

0.150

0.157

1.27

0.050

5.80

6.20

0.228

0.244

0.40

1.27

0.016

0.050

0.00

0.10

0.000

0.004

0°

8°

0°

8°

Note:
1. PACKAGE BODY SIZES EXCLUDE MOLD FLASH
PROTRUSIONS OR GATE BURRS.
2. TOLERANCE 0.1000mm (4mil) UNLESS
OTHERWISE SPECIFIED
3. COPLANARITY: 0.1000mm
4. DIMENSION L IS MEASURED IN GAGE PLANE.
5. CONTROLLING DIMENSION IS MILLIMETER;
CONVERTED INCH DIMENSIONS ARE NOT
NECESSARILY EXACT.

Part Number AAT4650