AAT4601 Datasheet, PDF (10/14 Pages) Advanced Analogic Technologies – 1.5A Current Limited P-Channel Switch

AAT4601
1.5A Current Limited P-Channel Switch
Applications Information
Input Capacitor
The input capacitor serves two purposes. First, it
protects the source power supply from transient
current effects generated by the application load
circuit. If a short circuit is suddenly applied to the
output of an AAT4601, there is a microsecond long
period during which a large can current flow before
the current limit circuitry activates. Refer to the
characteristic curve named "Short Circuit Through
0.3Ω." A properly sized input capacitor can dramat-
ically reduce the load switch input transient
response effects seen by the power supply and
other circuitry upstream from the AAT4601.
The second purpose of the input capacitor is to
prevent transient events generated by the load cir-
cuit from affecting the operation of the AAT4601.
For example, if an AAT4601 is used in a circuit that
operates from a 3 volt power supply with poor step
load response, it is possible that turning on the load
switch could cause the input power supply to droop
below the AAT4601's under voltage lockout thresh-
old. This drop in voltage would cause the AAT4601
to turn off until the input power supply's voltage
recovers. Since this cycle would be self-perpetuat-
ing, the entire circuit could be seen to be unstable.
In the very rare case where capacitor cost is pro-
hibitive, the output load circuit should be slew rate
limited when turned on.
Output Capacitor
In order to insure stability while the device current
limit is active, a small capacitance of approximately
1µF should be used. When the AAT4601 is activat-
ed using the ON function, there are no momentary
current transients as in the case of when a short cir-
cuit suddenly applied to a device that is already on.
Refer to the characteristic curve named "Switch
Turn-On Time." No matter how big the output
capacitor, output current is limited to the value
allowed by the threshold determined by R_SET and
the internal current limiting circuitry. This permits
very large output capacitors to be used.
For example, USB ports are specified to have at
least 120µF of down stream capacitance from their
controlling power switch. An output capacitance as
large as 1000µF would not disturb the input power
supply to the AAT4601 used to control the USB port.
ON Input
When the AAT4601 is in the off state, the output is
an open circuit and the device quiecent current
consumption is reduced to less than 1µA. The ON
threshold voltage is set to allow the AAT4601 to be
controlled by 5 volt TTL levels as well as CMOS
power from 2.5 volts to 5 volts. The ON function
control voltage level should not exceed the input
supply level applied to the IN pin.
FAULT Output
A FAULT flag is provided to alert a system if the load
switch is not receiving a sufficient voltage level to
operate properly. If either the current limit or over
temperature circuits in any combination are active
for more than approximately two milliseconds con-
tinuously, the FAULT pin is pulled to ground inter-
nally through a 100Ω resistance. The 2 millisecond
delay on the FAULT function is intended to prevent
capacitive loads connected to the load switch out-
put from activating FAULT when the device is
turned on. The placement of a pull up resistor
between the FAULT pin and the IN pin is recom-
mended. Reasonable values for the pull up resistor
should range from 10kΩ to 100kΩ. Since FAULT is
an open drain terminal, it may be pulled up to any
voltage that is not greater than the level present on
the IN pin. This is done to allow the AAT4601 to sig-
nal ancillary circuitry that is powered by voltage
level less than the level on the IN pin.
Reverse Voltage
The AAT4601 is designed to control current flowing
from IN to OUT. If a voltage is applied to OUT
which is greater than that on IN, a large resulting
reverse current may flow, potentially damaging the
AAT4601.
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4601.2001.11.0.92