aoz1022di-01 Alpha & Omega Semiconductor, aoz1022di-01 Datasheet - Page 7

• Manufacturer Part Number: aoz1022di-01
• Description: Ezbucktm 3a Synchronous Buck Regulator
• Manufacturer: Alpha & Omega Semiconductor

Detailed Description
The AOZ1022 is a current-mode step down regulator
with integrated high-side PMOS switch and a low-side
NMOS switch. It operates from a 4.5V to 16V input
voltage range and supplies up to 3A 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, output over voltage protection, active high power
good state, fixed internal soft-start and thermal shut
down.
The AOZ1022 is available in an DFN 5x4 package.
Enable and Soft Start
The AOZ1022 has an 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 4.1V and voltage
on EN pin is HIGH. In the soft start process, the output
voltage is typically ramped to regulation voltage in 4ms.
The 4ms soft start time is set internally.
The EN pin of the AOZ1022 is active HIGH. Connect the
EN pin to V
Pulling EN to ground will disable the AOZ1022. Do not
leave it open. The voltage on the EN pin must be above
2V to enable the AOZ1022. When voltage on the EN
pin falls below 0.6V, the AOZ1022 is disabled. If an appli-
cation circuit requires the AOZ1022 to be disabled, an
open drain or open collector circuit should be used to
interface to the EN pin.
Power Good
The output of Power-Good is an open drain N-channel
MOSFET which supplies an active high power good
stage. A pull-up resistor (R
DC power trail with maximum voltage of 6V. The
AOZ1022 monitors the FB voltage. When FB voltage is
lower than 90% of the normal voltage, N-channel
MOSFET turns on and the Power-Good pin is pulled low.
This indicates the power is abnormal.
Steady-State Operation
Under steady-state conditions, the converter operates in
fixed frequency and Continuous-Conduction Mode
(CCM).
The AOZ1022 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
Rev.3.0 November 2011
IN
if the enable function is not used.
3
) should connect this pin to a
www.aosmd.com
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 the
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 internal low-side N-MOSFET
switch to output. The internal adaptive FET driver
guarantees no turn on overlap of both high-side and
low-side switch.
Comparing with regulators using freewheeling Schottky
diodes, the AOZ1022 uses freewheeling NMOSFET to
realize synchronous rectification. It greatly improves the
converter efficiency and reduces power loss in the
low-side switch.
The AOZ1022 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 high-side 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 the equation below:
where;
V
V
I
R
between 97m
junction temperature.
Switching Frequency
The AOZ1022 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 by using a resistor divider network. See the
application circuit shown in Figure 1. The resistor divider
network includes R
by picking a fixed R
R
V
O
V
O_MAX
IN
DS(ON)
1
O
is the output current from 0A to 3A, and
O_MAX
with equation:
is the input voltage from 4.5V to 16V,
=
IN
0.8
is the maximum output voltage,
is the on resistance of internal MOSFET, the value is
to V
=

Ω
O



V
and 200m
1
is the load current x DC resistance of
IN
+
–
R
------ -
R
1
2
I
and R
1
2
O
value and calculating the required




Ω
R
depending on input voltage and
2
DS ON
. Usually, a design is started


AOZ1022DI-01
Page 7 of 15