AAT4626_08 Datasheet, PDF (9/15 Pages) Advanced Analogic Technologies – USB Dual-Channel Power Switch

SmartSwitch^TM
Output Capacitor
In order to insure stability while the device current limit
is active, a small capacitance of approximately 1μF
should be used on each output. When either output of
the AAT4626 is activated using the EN(A/B) function,
there are no momentary current transients, as in the
case when a short circuit is suddenly applied to a device
that is already on. Refer to the Typical Characteristics
curve “Turn-On/Off Response.” Regardless of output
capacitor size, output current on either output is limited
to the value allowed by the threshold determined by the
internal current limiting circuitry. Refer to the internal
current limit threshold specifications stated in the
Electrical Characteristics section of this datasheet. This
permits very large output capacitors to be used.
For example, USB ports are specified to have at least
120μF of downstream capacitance from their controlling
power switch. An output capacitance as large as 1000μF
would not disturb the input power supply to an AAT4626
used to control a USB port.
EN Inputs
The AAT4626 has two enable inputs, ENA and ENB.
These two enable inputs allow the AAT4626 to indepen-
dently control each respective output. The device is
available in both active high EN enable and active low
(EN) enable versions. For specific part numbers, refer to
the ordering information section. When both the A and
B outputs of the AAT4626 are in the off state, the
respective outputs are an open circuit and the device
quiescent current consumption is reduced to less than
1μA. The ENA and ENB threshold voltages are set to
allow the AAT4626 to be controlled by 5V TTL levels, as
well as CMOS-compatible levels ranging from 2.5V to 5V.
The ENA or ENB function control voltage levels should
not exceed the input supply level applied to the IN pin.
Fault Flag Output
The AAT4626 features an active low fault flag (FLGA and
FLGB) output for each A and B output channel. The fault
flags are provided to alert the system if the over-current
or over-temperature circuits become active, or if the
load switch is not receiving a sufficient voltage level to
properly operate. If either the current limit or over-
temperature circuits in any combination are constantly
PRODUCT DATASHEET
AAT4626
USB Dual-Channel Power Switch
active for more than approximately ten milliseconds, the
FLG(A/B) pin is pulled to ground internally through an
open drain device. The 10ms delay on the fault function
is intended to prevent capacitive loads connected to one
of the load switch outputs from activating its respective
flag when the device is turned on. The placement of a
pull-up resistor between the FLGA or FLGB pin and the
IN pin is recommended. Reasonable values for the pull-
up resistor should range from 10kΩ to 100kΩ. Since the
fault flags are open drain terminals, they may be pulled
up to any voltage that is not greater than the level pres-
ent on the IN pin. This is done to allow the AAT4626 to
signal ancillary circuitry that is powered by voltage lev-
els less than the level on the IN pin.
If a fault flag delay greater than 10ms is required, addi-
tion delay may be added by use of an RC filter. As shown
in Figure 1, an RC filter can be added to the fault flag
output.
V+
USB Controller
Over-Current
Flag Input
R1
10kΩ
C1
0.1µF
100kΩ _AAT4626
1 _{ENA OUTA} 8
2 _{FLGA IN} 7
3 _{FLGB GND} 6
4 _{ENB OUTB} 5
Figure 1: Fault Flag Delay RC Filter.
Reverse Voltage
The AAT4626 is designed to control current flowing from
IN to OUT. If a voltage is applied to OUT which is great-
er than that on IN, a large resulting reverse current may
flow, potentially damaging the AAT4626.
Under-Voltage Lockout
The AAT4626 has been designed with an under-voltage
lockout control circuit. The under-voltage lockout pre-
vents the output MOSFET devices from turning on until
V_IN exceeds the typical UVLO threshold of 2.3V. During
operation, the device will automatically shut down if V_IN
falls below the UVLO threshold and the fault flags will be
toggled.
4626.2008.02.1.3
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