aoz1038di Alpha & Omega Semiconductor, aoz1038di Datasheet - Page 6

• Manufacturer Part Number: aoz1038di
• Description: Ezbucktm 6 A Synchronous Buck Regulator
• Manufacturer: Alpha & Omega Semiconductor

Table 1.
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 the
inductor.
Protection Features
The AOZ1038 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 AOZ1038 employs peak
current mode control, the COMP pin voltage is
proportional to the peak inductor current. The COMP pin
voltage is limited internally to be between 0.4 V and 2.5 V.
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 slowly during
a switching cycle because of V
catastrophic failure, a secondary current limit is designed
inside the AOZ1038. The measured inductor current is
compared against a preset voltage which represents the
current limit. When the output current is more than
current limit, the high side switch is turned off. The
converter will initiate a soft start once the over-current
condition is resolved.
Power-On Reset (POR)
A power-on reset circuit monitors the input voltage.
When the input voltage exceeds 4.1 V, the converter
starts operation. When input voltage falls below 3.7 V,
the converter will shut down.
Rev. 1.2 February 2011
Vo (V)
0.8
1.2
1.5
1.8
2.5
3.3
5.0
1
and R
R1 (kΩ)
4.99
12.7
21.5
31.1
52.3
1.0
10
2
should be large enough to
O
= 0 V. To prevent
R2 (kΩ)
Open
10.2
11.5
10
10
10
10
www.aosmd.com
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 ºC. The regulator will restart automatically under the
control of the soft-start circuit when the junction
temperature decreases to 100 ºC.
Application Information
The basic AOZ1038 application circuit is show in
Figure 1. Component selection is explained below.
Input Capacitor
The input capacitor must be connected to the V
the PGND pin of the AOZ1038 to maintain steady input
voltage and to filter out pulsing input current. The voltage
rating of the 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 the input capacitor current
can be calculated by:
if we let m equal the conversion ratio:
The relationship 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 V
stress. The worst current stress on C
I
ΔV
-------- -
V
CIN_RMS
V
IN
O
IN
=
O
=
m
is half of V
---------------- -
f
×
=
I
O
C
I
O
IN
×
×
IN
⎛
⎜
⎝
, C
-------- - 1
V
1
V
IN
–
O
IN
-------- -
V
V
⎛
⎜
⎝
is under the worst current
IN
O
–
⎞
⎟
⎠
-------- -
V
V
×
IN
O
-------- -
V
V
⎞
⎟
⎠
IN
O
IN
is 0.5 x I
AOZ1038
Page 6 of 14
IN
O
pin and
.