aoz1012d Alpha & Omega Semiconductor, aoz1012d Datasheet - Page 7

• Manufacturer Part Number: aoz1012d
• Description: Ezbuck 3a Simple Regulator
• Manufacturer: Alpha & Omega Semiconductor

The combination of R
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 AOZ1012D has multiple protection features to pre-
vent system circuit damage under abnormal conditions.
Over Current Protection (OCP)
The sensed inductor current signal is also used for
over current protection. Since the 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 stops 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 the cycle by cycle current limit circuit is triggered,
the output voltage drops as the duty cycle is decreasing.
The AOZ1012D 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 equal 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.
Rev. 1.2 February 2007
1
and R
2
should be large enough to
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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
145°C. The regulator will restart automatically under the
control of soft-start circuit when the junction temperature
decreases to 100°C.
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 V
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 the
equation below:
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:
If let m equal the conversion ratio:
The relationship between the input capacitor RMS cur-
rent and voltage conversion ratio is calculated and shown
in Figure 2 on the next page. It can be seen that when V
is half of V
worst current stress on C
--------- -
V
I
V
CIN _RMS
V
IN
O
IN
=
=
m
------------------ -
f
IN
=
, C
I
O
C
I
IN
O
IN
is under the worst current stress. The
--------- - 1
V
1
V
IN
–
O
IN
--------- -
V
V
is 0.5 x I
IN
O
–
--------- -
V
V
IN
O
--------- -
V
V
O
IN
O
.
AOZ1012D
Page 7 of 15
IN
pin and
O