APL3512
Function Description
VIN Under-Voltage Lockout (UVLO)
VIN is the amplitude of input voltage applied to this device,
of which unit is volt.
The APL3512A/B power switch is built-in an under-volt-
age lockout circuit to keep the output shut off until internal
circuitry is operating properly. The UVLO circuit has hys-
teresis and a de-glitch feature so that it will typically ig-
nore undershoot transients on the input. When input volt-
age exceeds the UVLO threshold, the output voltage starts
a soft-start to reduce the inrush current.
If the CSS is not connected or SS pin is tied to VIN, the soft-
start time is 2ms when VIN=5V.
Enable/Disable
Pull the ENB above 2V, or EN below 0.8V to disable the
device and pull ENB pin below 0.8V or EN above 2V to
enable the device. When the IC is disabled, the supply
current is reduced to less than 1mA. The enable input is
compatible with both TTL and CMOS logic levels. The
EN/ENB pins cannot be left floating.
Power Switch
The power switch is an N-channel MOSFET with a low
RDS(ON). The internal power MOSFET does not have the
body diode. When IC is off, the MOSFET prevents a cur-
rent flowing from the VOUT back to VIN and VIN to VOUT.
Over-Temperature Protection
When the junction temperature exceeds 140oC, 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 20oC, 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 TJ=+125oC.
Current-Limit Protection
The APL3512A/B power switch provides the current-limit
protection function. During current-limit, the devices 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 VIN-1.5V, which is
caused by the over load or 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 condition. If the junction temperature is
over the thermal shutdown temperature, the device will
enter the thermal shutdown.
Soft-Start
The APLA3512A/B provides an adjustable soft-start cir-
cuitry to control rise rate of the output voltage and limit the
current surge during start-up. The soft-start ramp-up rate
is controlled by a capacitor from SS pin to the ground.
Under a specific VIN being applied to the APL3512A/B, the
soft start time can be calculated by the following equation:
tSS = 0.2 x CSS x VIN
where,
tSS is soft-start time of VOUT rising from 0 to 100%, of which
unit is second.
CSS is the value of the capacitor connected from SS pin to
GND, of which unit is micro-Farad.
Copyright ã ANPEC Electronics Corp.
12
www.anpec.com.tw
Rev. A.6 - Aug., 2012
ANPEC [ ANPEC ELECTRONICS COROPRATION ]
