aoz1014 Alpha & Omega Semiconductor, aoz1014 Datasheet - Page 7

• Manufacturer Part Number: aoz1014
• Description: Ezbuck 5a Simple Buck Regulator
• Manufacturer: Alpha & Omega Semiconductor

Detailed Description
The AOZ1014 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 AOZ1014 is available in SO-8 and thermally
enhanced DFN-8 package.
Enable and Soft Start
The AOZ1014 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 4ms.
The 4ms soft start time is set internally.
The EN pin of the AOZ1014 is active high. Connect the
EN pin to V
ground will disable the AOZ1014. Do not leave it open.
The voltage on EN pin must be above 2.0V to enable the
AOZ1014. When voltage on EN pin falls below 0.6V, the
AOZ1014 is disabled. If an application circuit requires the
AOZ1014 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 AOZ1014 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 volt-
age, 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 free-
wheeling through the external Schottky diode to output.
Rev. 1.0 December 2006
IN
if enable function is not used. Pulling EN to
www.aosmd.com
The AOZ1014 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
V
MOSFET plus DC resistance of buck inductor. It can be
calculated by equation below:
where;
V
V
I
R
between 25m and 55m depending on input voltage and
junction temperature, and
R
Switching Frequency
The AOZ1014 switching frequency is fixed and set by an
internal oscillator. The practical switching frequency
could range from 350kHz 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
application 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
V
O
O_MAX
IN
0.8
1.2
1.5
1.8
2.5
3.3
5.0
IN
DS(ON)
inductor
1
O
O _MAX
is the output current from 0A to 5A,
with equation below:
is the input voltage from 4.5V to 16V,
to V
=
V
is the maximum output voltage,
0.8
O
O
is the on resistance of internal MOSFET, the value is
is the inductor DC resistance.
(V)
is the load current times DC resistance of
=
V
1
IN
+
–
R
------ -
R
1
2
1.0
4.99
10
12.7
21.5
31.6
52.3
I
and R
value and calculating the required
1
2
O
R
1
R
2
1
. Usually, a design is started
(k )
DS ON
and R
2
for the most com-
+
R
Open
10
11.5
10.2
10
10
10
inductor
AOZ1014
R
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(k )