aoz1056 Alpha & Omega Semiconductor, aoz1056 Datasheet - Page 7

• Manufacturer Part Number: aoz1056
• Description: Ezbucktm 2a Simple Buck Regulator
• Manufacturer: Alpha & Omega Semiconductor

Detailed Description
The AOZ1056 is a current-mode step down regulator with
integrated high side PMOS switch and a low side free-
wheeling Schottky diode. It operates from a 4.5V to 16V
input voltage range and supplies up to 2A of load
current. The duty cycle can be adjusted from 6% to 100%
allowing a wide range of output voltages. Features
include enable control, under voltage lockout, external
soft-start, output over-voltage protection, over-current
protection and thermal shut down.
The AOZ1056 is available in an SO-8 package.
Enable and Soft Start
The AOZ1056 has an external 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, a 5µA internal current
source charges the external capacitor at SS. As the SS
capacitor is charged, the voltage at SS rises. The SS
voltage clamps the reference voltage of the error ampli-
fier, therefore output voltage rising time follows the SS pin
voltage. With the slow ramping up output voltage, the
inrush current can be prevented. For proper start-up and
operation of the IC, the minimum external soft-start
capacitor required is 780pF, and the corresponding
soft-start time is about 100µs. The graph below shows the
soft-start capacitance and the corresponding soft-start
time.
A simple equation can also be used to choose the soft-
start capacitor according to the desired soft-start time:
The EN pin of the AOZ1056 is active high. Connect the
EN pin to V
ground will disable the AOZ1056. Do not leave it open.
Css nf
Rev. 1.2 September 2008
( )
16
14
12
10
8
6
4
2
0
≈
0
IN
6.9 Tss ms
if enable function is not used. Pulling EN to
×
20
Soft-Start Capacitor (nF)
(
40
)
60
80
100
www.aosmd.com
The voltage on EN pin must be above 2.0V to enable the
AOZ1056. When voltage on EN pin falls below 0.6V, the
AOZ1056 is disabled. If an application circuit requires the
AOZ1056 to be disabled, an open drain or open collector
circuit should be used to interface to the EN pin.
Steady-State Operation
Under steady-state conditions, the converter operates in
fixed frequency and Continuous-Conduction Mode (CCM).
The AOZ1056 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 freewheel-
ing through the internal Schottky diode to output.
The AOZ1056 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
regulation mode of operation. The minimum voltage drop
from V
MOSFET + DC resistance of buck inductor. It can be
calculated by equation below:
where;
V
V
I
R
between 97mΩ and 200mΩ depending on input voltage and
junction temperature, and
R
Switching Frequency
The AOZ1056 switching frequency is fixed at 340kHz and
set by an internal oscillator.
O
V
O_MAX
IN
DS(ON)
inductor
is the output current from 0A to 2A,
O_MAX
is the input voltage from 4.5V to 16V,
IN
is the maximum output voltage,
is the on resistance of internal MOSFET, the value is
is the inductor DC resistance.
to V
=
O
V
is the load current x DC resistance of
IN
–
I
O
×
(
R
DS ON
(
)
+
R
inductor
AOZ1056
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