APL3518 Datasheet, PDF (13/21 Pages) Anpec Electronics Coropration – USB Power-Distribution Switches

APL3518/9
Function Description
VIN Under-Voltage Lockout (UVLO)
The APL3518/9 series of power switches have a built-in
under-voltage lockout circuit to keep the output shutting
off until internal circuitry is operating properly. The UVLO
circuit has hysteresis and a de-glitch feature so that it will
typically ignore undershoot transients on the input. When
input voltage exceeds the UVLO threshold, the output
voltage starts a soft-start to reduce the inrush current.
Power Switch
The power switch is an N-channel MOSFET with a low
R . The internal power MOSFET does not have the
DS(ON)
body diode. When IC is off, the MOSFET prevents a cur-
rent flowing from the VOUT back to VIN and VIN to VOUT.
compatible with both TTL and CMOS logic levels. The
EN/ENB pin cannot be left floating.
Over-Temperature Protection
When the junction temperature exceeds 140^oC, the inter-
nal thermal sense circuit turns off the power FET and
allows the device to cool down. When the device’s junc-
tion temperature cools by 20^oC, the internal thermal
sense circuit will enable the device, resulting in a pulsed
output during continuous thermal protection. Thermal
protection is designed to protect the IC in the event of
over temperature conditions. For normal operation, the
junction temperature cannot exceed T =+125^oC.
J
Current-Limit Protection
The APL3518/9 series of power switches provide the cur-
rent-limit protection function. During current-limit, the de-
vices limit output current at current limit threshold. For
reliable operation, the device should not be operated in
current-limit for extended period.
Short-Circuit Protection
When the output voltage drops below 1.5V, which is
caused by an over-load or a short-circuit, the devices limit
the output current down to a safe level. The short-circuit
current limit is used to reduce the power dissipation dur-
ing short-circuit conditions. If the junction temperature
reaches over-temperature threshold, the device will en-
ter the thermal shutdown.
OCB Output
The APL3158/9 series of power switches provide an
open-drain output to indicate that a fault has occurred.
When any of current-limit or over-temperature protection
occurs for a deglitch time of t_D(OCB), the OCB goes low.
Since the OCB pin is an open-drain output, connecting a
resistor to a pull high voltage is necessary.
Enable/Disable
Pull the ENB above 2V or EN below 0.8V will disable the
device, and pull ENB pin below 0.8V or EN above 2V will
enable the device. When the IC is disabled, the supply
current is reduced to less than 1µA. The enable input is
Copyright © ANPEC Electronics Corp.
13
Rev. A.3 - Apr., 2011
www.anpec.com.tw