aoz1094 Alpha & Omega Semiconductor, aoz1094 Datasheet - Page 8

• Manufacturer Part Number: aoz1094
• Description: Ezbucktm 5a Simple Buck Regulator
• Manufacturer: Alpha & Omega Semiconductor

Detailed Description
The AOZ1094 is a current-mode step down regulator
with integrated high side PMOS switch and a low side
freewheeling Schottky diode. It operates from a 4.5V to
16V input voltage range and supplies up to 5A of load
current. The duty cycle can be adjusted from 6% to 100%
allowing a wide range of output voltage. Features include
enable control, Power-On Reset, input under voltage
lockout, fixed internal soft-start and thermal shut down.
The AOZ1094 is available in SO-8 and thermally
enhanced DFN-8 package.
Enable and Soft Start
The AOZ1094 has internal soft start feature to limit
in-rush current and ensure the output voltage ramps up
smoothly to regulation voltage. A soft start process
begins when the input voltage rises to 4.0V and voltage
on EN pin is HIGH. In soft start process, the output
voltage is ramped to regulation voltage in typically 3ms.
The 3ms soft start time is set internally.
The EN pin of the AOZ1094 is active high. Connect the
EN pin to V
ground will disable the AOZ1094. Do not leave it open.
The voltage on EN pin must be above 2.0V to enable
the AOZ1094. When voltage on EN pin falls below 0.6V,
the AOZ1094 is disabled. If an application circuit requires
the AOZ1094 to be disabled, an open drain or open
collector circuit should be used to interface to EN pin.
Steady-State Operation
Under steady-state conditions, the converter operates in
fixed frequency and Continuous-Conduction Mode
(CCM).
The AOZ1094 integrates an internal P-MOSFET as the
high-side switch. Inductor current is sensed by amplifying
the voltage drop across the drain to source of the high
side power MOSFET. Output voltage is divided down by
the external voltage divider at the FB pin. The difference
of the FB pin voltage and reference is amplified by the
internal transconductance error amplifier. The error
voltage, which shows on the COMP pin, is compared
against the current signal, which is sum of inductor
current signal and ramp compensation signal, at PWM
comparator input. If the current signal is less than the
error voltage, the internal high-side switch is on. The
inductor current flows from the input through the inductor
to the output. When the current signal exceeds the error
voltage, the high-side switch is off. The inductor current
is freewheeling through the external Schottky diode to
output.
Rev. 1.3 October 2010
IN
if enable function is not used. Pulling it to
www.aosmd.com
The AOZ1094 uses a P-Channel MOSFET as the high
side switch. It saves the bootstrap capacitor normally
seen in a circuit which is using an NMOS switch. It allows
100% turn-on of the upper switch to achieve linear regu-
lation mode of operation. The minimum voltage drop from
VIN to VO is the load current times DC resistance of
MOSFET plus DC resistance of buck inductor. It can be
calculated by equation below:
where;
V
V
I
R
between 25m
junction temperature, and
R
Switching Frequency
The AOZ1094 switching frequency is fixed and set by an
internal oscillator. The practical switching frequency
could range from 400kHz to 600kHz due to device
variation.
Output Voltage Programming
Output voltage can be set by feeding back the output to
the FB pin with a resistor divider network. In the appli-
cation circuit shown in Figure 1. The resistor divider
network includes R
by picking a fixed R
R
Some standard values of R
monly used output voltage values are listed in Table 1.
Table 1.
V
O
V
O_MAX
IN
DS(ON)
inductor
1
O
is the output current from 0A to 5A,
O_MAX
with equation below
is the input voltage from 4.5V to 16V,
=
V
0.8
is the maximum output voltage,
is the on resistance of internal MOSFET, the value is
is the inductor DC resistance.
O
0.8
1.2
1.5
1.8
2.5
3.3
5.0
(V)
=
×
Ω
⎛
⎜
⎝
V
and 55m
1
IN
+
–
R
------ -
R
1
2
I
and R
1
2
O
value and calculating the required
⎞
⎟
⎠
Ω
×
R
depending on input voltage and
(
1
R
4.99
12.7
21.5
31.6
52.3
2
1.0
1
10
. Usually, a design is started
(k
DS ON
and R
Ω
(
)
2
)
for the most com-
+
R
inductor
AOZ1094
R
Page 8 of 19
Open
2
11.5
10.2
10
10
10
10
(k
Ω
)
)