AOZ1019AI Ver la hoja de datos (PDF) - Alpha and Omega Semiconductor
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AOZ1019AI Datasheet PDF : 14 Pages
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AOZ1019
The combination of R2 and R3 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
The AOZ1019 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 the AOZ1019 employs peak
current mode control, the COMP pin voltage is propor-
tional 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
2.5A and 3.6A. When the load current reaches the cur-
rent 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 due to the limitation on peak inductor current.
When cycle by cycle current limit circuit is triggered, the
output voltage drops as the duty cycle decreasing.
The AOZ1019 has internal short circuit protection 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.
Output Over Voltage Protection (OVP)
The AOZ1019 monitors the feedback voltage: when the
feedback voltage is higher than 960mV, it immediate
turns-off the PMOS to protect the output voltage over-
shoot at fault condition. When feedback voltage is lower
than 860mV, the PMOS is allowed to turn on in the next
cycle.
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.
Schottky Diode Selection
The external freewheeling diode supplies the current to
the inductor when the high side PMOS switch is off. To
reduce the losses due to the forward voltage drop and
recovery of diode, Schottky diode is recommended to
use. The maximum reverse voltage rating of the chosen
Schottky diode should be greater than the maximum
input voltage, and the current rating should be greater
than the maximum load current.
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
150°C.
Application Information
The basic AOZ1019 application circuit is shown in
Figure 1. Component selection is explained below.
Input Capacitor
The input capacitor (C1 in Figure 1) must be connected
to the VIN pin and PGND pin of the AOZ1019 to maintain
steady input voltage and filter out the pulsing input
current. A small decoupling capacitor (Cd in Figure 1),
usually 1µF, should be connected to the VIN pin and
AGND pin for stable operation of the AOZ1019. 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:
∆V IN
=
-------I--O---------
×
1
–
-V-----O----
×
-V-----O----
f × CIN V IN V IN
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 ×
-V-----O----
1
–
-V-----O----
V IN V IN
Rev. 1.0 September 2007
www.aosmd.com
Page 7 of 14
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