AOZ1031AI Alpha & Omega Semiconductor Inc, AOZ1031AI Datasheet - Page 8

• Manufacturer Part Number: AOZ1031AI
• Description: IC BUCK SYNC ADJ 3A SO8
• Manufacturer: Alpha & Omega Semiconductor Inc
• Series: EZBuck™r
• Type: Step-Down (Buck), PWM - Current Moder

Specifications of AOZ1031AI

• Featured Product: The AOZ103x Family Synchronous Buck Regulator
• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.8 V ~ 18 V
• Current - Output: 3A
• Frequency - Switching: 600kHz
• Voltage - Input: 4.5 V ~ 18 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 785-1253-2

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
inductor.
Protection Features
The AOZ1031A 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 AOZ1031A employs peak
current mode control, the COMP pin voltage is propor-
tional to the peak inductor current. The COMP pin volt-
age 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 condi-
tions, the inductor current decays very slow during a
switching cycle because of V
strophic failure, AOZ1031A detects the duration the over-
current condition occurs. If the over-current condition
occurs for certain period, AOZ1013A totally turns off for a
period of time, then restarts. If the fault is still there, then
the chip will be off again. The converter will initiate a soft
start once the over-current condition disappears.
Rev. 1.6 March 2010
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
o
2
=0V. To prevent cata-
should be large enough to
R2 (kΩ)
open
10.2
11.5
10
10
10
10
www.aosmd.com
Power-On Reset (POR)
A power-on reset circuit monitors the input voltage. When
the input voltage exceeds 4.1V, the converter starts oper-
ation. 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
150
control of soft-start circuit when the junction temperature
decreases to 100
Application Information
The basic AOZ1031A application circuit is show in
Figure 1. Component selection is explained below.
Input Capacitor
The input capacitor must be connected to the V
PGND pin of AOZ1031A 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 equa-
tion 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 calcu-
lated 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 V
half of V
worst current stress on C
I
CIN_RMS
ΔV
-------- -
V
V
IN
°
O
C. The regulator will restart automatically under the
IN
=
IN
=
m
, C
---------------- -
f
=
×
IN
I
O
C
I
O
is under the worst current stress. The
IN
°
×
C.
×
⎛
⎜
⎝
-------- - 1
V
V
1
IN
O
–
IN
⎛
⎜
⎝
-------- -
V
V
is 0.5 x I
IN
O
–
⎞
⎟
⎠
-------- -
V
V
×
IN
O
-------- -
V
V
⎞
⎟
⎠
IN
O
O
.
AOZ1031AI
Page 8 of 15
IN
pin and
O
is