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AOZ1034 Datasheet(PDF) 8 Page - Alpha & Omega Semiconductors

Part No. AOZ1034
Description  EZBuck™ 4A Synchronous Buck Regulator
Download  18 Pages
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Maker  AOSMD [Alpha & Omega Semiconductors]
Homepage  http://www.aosmd.com
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AOZ1034 Datasheet(HTML) 8 Page - Alpha & Omega Semiconductors

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AOZ1034
Rev. 1.1 September 2010
www.aosmd.com
Page 8 of 18
Table 1.
The combination of R1 and R2 should be large enough to
avoid drawing excessive current from the output, which
will cause power loss.
Protection Features
The AOZ1034 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 AOZ1034 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.
When the output is shorted to ground under fault
conditions, the inductor current decays very slow during
a switching cycle because of VO = 0V. To prevent
catastrophic failure, a secondary current limit is designed
inside the AOZ1034. The measured inductor current is
compared against a preset voltage which represents the
current limit, between 2.5A and 3.6A. When the output
current is more than current limit, the high side switch will
be turned off. The converter will initiate a soft start once
the over-current condition disappears.
Power-On Reset (POR)
A power-on reset circuit monitors the input voltage.
When the input voltage exceeds 4.1V, the converter
starts operation. When input voltage falls below 3.7V,
the converter will be shut down.
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
150ºC. The regulator will restart automatically under the
control of soft-start circuit when the junction temperature
decreases to 100ºC.
Application Information
The basic AOZ1034 application circuit is show in
Figure 1. Component selection is explained below.
Input Capacitor
The input capacitor must be connected to the VIN pin and
PGND pin of AOZ1034 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 con-
verter, 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 we let m equal the conversion ratio:
The relation between the input capacitor RMS current
and voltage conversion ratio is calculated and shown in
Figure 2 on the next page. 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 x IO.
Vo (V)
R1 (k
Ω)
R2 (k
Ω)
0.8
1.0
Open
1.2
4.99
10
1.5
10
11.5
1.8
12.7
10.2
2.5
21.5
10
3.3
31.1
10
5.0
52.3
10
ΔV
IN
I
O
fC
IN
×
-----------------
1
V
O
V
IN
---------
⎝⎠
⎜⎟
⎛⎞
V
O
V
IN
---------
×
×
=
I
CIN_RMS
I
O
V
O
V
IN
--------- 1
V
O
V
IN
---------
⎝⎠
⎜⎟
⎛⎞
×
=
V
O
V
IN
---------
m
=


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