APW7314AZI-TRG データシートの表示（PDF） - Anpec Electronics
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APW7314AZI-TRG Datasheet PDF : 18 Pages
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APW7314
Function Description
Main Control Loop
The APW7314 is a constant frequency, synchronous rec-
tifier and current-mode switching regulator. In normal
operation, the internal upper power MOSFET is turned on
each cycle. The peak inductor current at which ICMP turn
off the upper MOSFET is controlled by the voltage on the
COMP node, which is the output of the error amplifier
(EAMP). An external resistive divider connected between
VOUT and ground allows the EAMP to receive an output
feedback voltage VFB at FB pin. When the load current
increases, it causes a slightly decrease in VFB relative to
the 0.807V reference, which in turn causes the COMP
voltage to increase until the average inductor current
matches the new load current.
Enable/Shutdown
Driving EN to the ground places the APW7314 in shut-
down mode. When in shutdown, the internal power
MOSFETs turn off, all internal circuitry shuts down and
the quiescent supply current reduces to 1µA typical.
Under Voltage Lockout (UVLO)
An under-voltage lockout function prevents the device from
operating if the input voltage on VIN is lower than approxi-
mately 3.9V. The device automatically enters the shut-
down mode if the voltage on VIN drops below approxi-
mately 3.9V. This under-voltage lockout function is imple-
mented in order to prevent the malfunctioning of the
converter.
Soft-Start
The APW7314 has a built-in soft-start to control the output
voltage rise during start-up. During soft-start, an internal
ramp voltage, connected to the one of the positive inputs
of the error amplifier, raises up to replace the reference
voltage (0.807V typical) until the ramp voltage reaches
the reference voltage. Then, the voltage on FB regulated
at reference voltage.
Over-Current-Protection and Hiccup
The APW7314 has a cycle-by-cycle over-current limit when
the inductor current peak value exceeds the set current
limit threshold. Meanwhile, the output voltage drops until
FB is below the Under-Voltage (UV) threshold below the
reference. Once UV is triggered, the APW7314 enters hic-
cup mode to periodically restart the part. This protection
mode is especially useful when the output is dead-shorted
to ground. The average short circuit current is greatly re-
duced to alleviate thermal issues and to protect the
regulator. The APW7314 exits the hiccup mode once the
over-current condition is removed.
Over-Temperature Protection (OTP)
The over-temperature circuit limits the junction tempera-
ture of the APW7314. When the junction temperature ex-
ceeds 150oC, a thermal sensor turns off the both power
MOSFETs, allowing the devices to cool. The thermal sen-
sor allows the converters to start a soft-start process and
regulate the output voltage again after the junction tem-
perature cools by 30oC. The OTP is designed with a 30oC
hysteresis to lower the average Junction Temperature
(T ) during continuous thermal overload conditions, in-
J
creasing the lifetime of the device.
Over-Voltage Protection (OVP)
The over-voltage function monitors the output voltage by
FB pin. Once the FB voltage exceeds 120% of the refer-
ence voltage, the over-voltage protection comparator
forces the low-side MOSFET on. This action actively pulls
down the output voltage to prevent the end device be
damage. As soon as the output voltage is below 105% of
the reference voltage, the low-side MOSFET off and the
OVP comparator is disengaged. The chip restores its
normal operation.
Copyright © ANPEC Electronics Corp.
10
Rev. A.2 - Aug., 2013
www.anpec.com.tw
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