AOZ1012DI 查看數據表（PDF） - Alpha and Omega Semiconductor
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AOZ1012DI Datasheet PDF : 17 Pages
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Combination of R1 and R2 should be large enough to
avoid drawing excessive current from the output, which
will cause power loss.
Since the switch duty cycle can be as high as 100%,
the maximum output voltage can be set as high as the
input voltage minus the voltage drop on upper PMOS
and inductor.
Protection Features
AOZ1012D has multiple protection features to prevent
system circuit damage under abnormal conditions.
Over Current Protection (OCP)
The sensed inductor current signal is also used for over
current protection. Since AOZ1012D employs peak
current mode control, the COMP pin voltage is
proportional to the peak inductor current. The COMP
pin voltage is limited to be between 0.4V and 2.5V
internally. The peak inductor current is automatically
limited cycle by cycle.
The cycle by cycle current limit threshold is set between
4A and 5A. When the load current reaches the current
limit threshold, the cycle by cycle current limit circuit
turns off the high side switch immediately to terminate
the current duty cycle. The inductor current stop rising.
The cycle by cycle current limit protection directly limits
inductor peak current. The average inductor current is
also limited since the limitation of peak inductor current.
When cycle by cycle current limit circuit is triggered, the
output voltage drops as the duty cycle decreasing.
The AOZ1012D has internal short circuit protection
circuit to protect itself from catastrophic failure under
output short circuit conditions. The FB pin voltage is
proportional to the output voltage. Whenever FB pin
voltage is below 0.2V, the short circuit protection circuit
is triggered. As a result, the converter is shut down and
hiccups at a frequency equals to 1/8 of normal
switching
frequency. The converter will start up via a soft start
once the short circuit condition disappears. In short
circuit protection mode, the inductor average current is
greatly reduced because of the low hiccup frequency.
Power-On Reset (POR)
A power-on reset circuit monitors the input voltage.
When the input voltage exceeds 4V, the converter starts
operation. When input voltage falls below 3.7V, the
converter will stop switching.
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Thermal Protection
An internal temperature sensor monitors the junction
temperature. It shuts down the internal control circuit
and high side PMOS if the junction temperature
exceeds 145ºC. The regulator will restart automatically
under the control of soft-start circuit when the junction
temperature decreases to 100ºC.
Application Information
The basic AOZ1012D application circuit is shown in
Figure 1. Component selection is explained below.
Input capacitor
The input capacitor must be connected to the VIN pin
and PGND pin of AOZ1012D to maintain steady input
voltage and filter out the pulsing input current. The
voltage rating of input capacitor must be greater than
maximum input voltage plus ripple voltage.
The input ripple voltage can be approximated by
equation below:
∆VIN
=
f
IO
× CIN
× (1 − VO ) × VO
VIN VIN
Since the input current is discontinuous in a buck
converter, the current stress on the input capacitor is
another concern when selecting the capacitor. For a
buck circuit, the RMS value of input capacitor current
can be calculated by:
ICIN _ RMS = IO ×
VO (1 − VO )
VIN
VIN
if let m equal the conversion ratio:
VO = m
VIN
The relation between the input capacitor RMS current
and voltage conversion ratio is calculated and shown in
Fig. 2 below. It can be seen that when VO is half of VIN,
CIN is under the worst current stress. The worst current
stress on CIN is 0.5·IO.
April 2006
www.aosmd.com
Page 9 of 17
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