AOZ1110QI Alpha & Omega Semiconductor Inc, AOZ1110QI Datasheet - Page 9

• Manufacturer Part Number: AOZ1110QI
• Description: IC BUCK SYNC ADJ 4A 24QFN
• Manufacturer: Alpha & Omega Semiconductor Inc
• Series: EZBuck™r
• Type: Step-Down (Buck), PWM - Current Moder

Specifications of AOZ1110QI

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.8 V ~ 5.5 V
• Current - Output: 4A
• Frequency - Switching: 500kHz, 1MHz
• Voltage - Input: 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-WFQFN Exposed Pad
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 785-1257-2

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 P-MOSFET and
inductor.
Protection Features
The AOZ1110QI 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 AOZ1110QI 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 0V and 2.2V internally.
The peak inductor current is automatically limited cycle
by cycle.
Power-On Reset (POR)
A power-on reset circuit monitors the input voltage. When
the input voltage exceeds 2.5V, the converter starts
operation. When input voltage falls below 2.3V, the
converter will be shut down.
Output Over Voltage Protection (OVP)
The AOZ1110QI monitors the feedback voltage: when
the feedback voltage is higher than 15% of set value, it
immediately turns off P-MOSFET cycle by cycle to
protect the output voltage overshoot at fault condition.
Thermal Protection
An internal temperature sensor monitors the junction
temperature. It shuts down both high side P-MOSFET
and low side N-MOSFET 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 AOZ1110QI 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 AOZ1110QI 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.
Rev. 1.0 October 2010
IN
pin and
www.aosmd.com
The input ripple voltage can be approximated by
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 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. It can be seen that when V
C
stress on C
For reliable operation and best performance, the input
capacitors must have current rating higher than I
at worst operating conditions. Ceramic capacitors are
preferred for input capacitors because of their low ESR
and high current rating. Depending on the application
circuits, other low ESR tantalum capacitor may also be
used. When selecting ceramic capacitors, X5R or X7R
type dielectric ceramic capacitors should be used for
their better temperature and voltage characteristics.
Note that the ripple current rating from capacitor
manufactures are based on certain amount of life time.
Further de-rating may be necessary in practical design.
-------- -
V
V
I
ΔV
CIN_RMS
IN
IN
O
is under the worst current stress. The worst current
I
CIN_RMS
IN
=
I
O
Figure 2. I
=
m
(m)
---------------- -
f
IN
×
=
I
0.5
0.4
0.3
0.2
0.1
is 0.5 x I
O
C
0
I
IN
O
0
CIN
×
×
vs. Voltage Conversion Ratio
⎛
⎜
⎝
1
-------- - 1
V
O
V
.
IN
–
O
-------- -
V
V
⎛
⎜
⎝
IN
O
–
⎞
⎟
⎠
-------- -
V
V
×
0.5
m
IN
O
-------- -
V
V
⎞
⎟
⎠
IN
O
O
is half of V
AOZ1110
Page 9 of 16
CIN_RMS
IN
1
,