AAT4650_06 ANALOGICTECH [Advanced Analogic Technologies], AAT4650_06 Datasheet - Page 9

• Manufacturer Part Number: AAT4650_06
• Description: 5V/3V PC Card Power Switch
• Manufacturer: ANALOGICTECH [Advanced Analogic Technologies]

Thermal issues are not a problem in the SOP-8
package since Θ
is only 120°C/W. At any given ambient temperature
(T
be determined by the following equation:
Constants for the AAT4650 are maximum junction
temperature, T
resistance, Θ
are calculated at the maximum operating tempera-
ture where T
culated under normal ambient conditions where T
= 25°C. At T
25°C, P
Maximum current is given by the following equation:
For the AAT4650 at 85°C, I
value greater than the internal minimum current
limit specification.
Over-Current and Over-Temperature
Protection
Because many AAT4650 applications provide power
to external devices, it is designed to protect its host
device from malfunctions in those peripherals
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
Other solutions, such as a poly fuse, do not protect
the host power supply and system from mishandling
or short circuiting 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.
Over-current and over-temperature go hand in hand.
Once an over-current condition exists, the current
supplied to the load by the AAT4650 is limited to the
4650.2006.05.1.2
A
) the maximum package power dissipation can
D(MAX)
A
JA
A
= 833mW.
J(MAX)
= 85°C. Typical conditions are cal-
= 85°C, P
= 120°C/W. Worst case conditions
P
JA
I
D(MAX)
OUT(MAX)
, the package thermal resistance,
= 125°C, and package thermal
=
=
T
D(MAX)
J(MAX)
θ
P
R
DS(ON)
JA
OUT(MAX)
D(MAX)
DS(ON)
-T
= 333mW. At T
A
for this function.
= 1.65A, a
A
=
A
over-current 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 over-temperature cir-
cuit is activated. If the temperature reaches the max-
imum level, the AAT4650 automatically switches off
the P-channel MOSFETs. While they are off, the
over-temperature 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 over-current cir-
cuit is not activated until a lower threshold of cur-
rent (approximately 500mA) is exceeded in the
power device. When the load current exceeds this
crude threshold, the AAT4650 quiescent current
increases from 15µA to 200µA. The high-speed
over-current circuit works by linearly limiting the
current when the current limit is reached. As the
voltage begins to drop on V
ing, the current limit magnitude varies and general-
ly decreases as the V
Switching V
The AAT4650 meets PC card standards for switch-
ing the V
V
card protocol for determining low voltage opera-
tions is to first power the peripheral with 5V and poll
for 3.3V operation. When transitioning from 5V to
3.3V, V
provide a hard reset. The resistive ground state
(CTL1 = 0, CTL0 = 0) will accommodate this. The
ground state will also guarantee the V
be discharged within the specified amount of time
(100ms).
Printed Circuit Board Layout
Recommendations
For proper thermal management, to minimize PCB
trace resistance, and to take advantage of the low
R
rules should be followed: V
be routed using wider than normal traces; the two
V
same wide PCB trace; and GND should be connect-
ed to a ground plane. For best performance, C
C
CC
CC
DS(ON)
OUT
, as well as a high impedance state. The PC
pins (Pins 6 and 7) should be connected to the
should be placed close to the package pins.
5V/3V PC Card Power Switch
CC
of the AAT4650, a few circuit board layout
CC
must be discharged to less than 0.8V to
output by providing a ground path for
CC
Voltage
CC
voltage drops to 0V.
CC3
CC
, V
due to current limit-
CC5
AAT4650
, and V
CC
voltage to
CC
should
IN
and
9