Copyright ANPEC Electronics Corp.
Rev. A.6 - Mar., 2011 www.anpec.com.tw9
APL5603
Function Description
Thermal Shutdown
A thermal shutdown circuit limits the junction tempera-
ture of APL5603. When the junction temperature exceeds
+150oC, the thermal shutdown circuitry disables the
output, which allows the device to cool down. The output
circuitry is enabled again after the junction temperature
cools down by 40oC, resulting in a pulsed output during
continuous thermal overload conditions. Thermal pro-
tection is designed to protect the IC in the event of over-
temperature conditions. For reliable operation, the junc-
tion temperature cannot exceed TJ=+125 oC.
Enable and Shutdown
Driving the EN high turns on the regulator, driving the EN
low puts the regulator into shutdown mode. A logic low
also causes the output voltage to discharge to the GND.
The EN is pulled low by an internal resistor.
Under-Voltage Lockout (UVLO)
The APL5603 regulator has a built-in under-voltage lock-
out circuit to keep the output shut off until internal circuitry
is operating properly. The UVLO function initiates a soft-
start process after input voltage exceeds its rising UVLO
threshold during power on. Typical UVLO threshold is
2.4V with 0.15V hysteresis.
Soft-Start
The APL5603 provides an internal soft-start circuitry to
control rise rate of the output voltage and limit the current
surge during start-up. Approximate 20µs delay time after
the VIN is over the UVLO threshold, the output voltage
starts the soft-start. The typical soft-start interval is about
130µs.
Current-Limit
The APL5603 provides a current-limit circuitry, which
monitors and controls P-MOS’s gate voltage, limiting the
output current to 700mA. For reliable operation, the de-
vice should not be operated in current-limit for extended
period.
Short-Circuit Current-Limit
When the output voltage drops below 0.6V due to over-
load or short-circuit, the internal short-circuit current-limit
circuitry limits the output current down to 250mA. The
short-circuit current-limit is used to reduce the power dis-
sipation during short-circuit condition. In some high VIN-
VOUT conditions, if the junction temperature is over the
thermal shutdown temperature, the device will enter the
thermal shutdown. Please refer to the section on thermal
considerations for power dissipation calculations. The
short-circuit current-limit has featured with blanking time
after the UVLO threshold is reached, so that it will avoid
the output causing short-circuit current-limit protection
during start-up; the blanking time is about 600µs.