AOZ1037PI Alpha & Omega Semiconductor Inc, AOZ1037PI Datasheet - Page 7

• Manufacturer Part Number: AOZ1037PI
• Description: IC BUCK SYNC ADJ 5A SO8
• Manufacturer: Alpha & Omega Semiconductor Inc
• Series: EZBuck™r
• Type: Step-Down (Buck), PWM - Current Moder

Specifications of AOZ1037PI

• Featured Product: The AOZ103x Family Synchronous Buck Regulator
• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.8 V ~ 18 V
• Current - Output: 5A
• Frequency - Switching: 500kHz
• Voltage - Input: 4.5 V ~ 18 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width) Exposed Pad
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 785-1256-2

Detailed Description
The AOZ1037 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 18V input voltage range
and supplies up to 5A of load current. 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 AOZ1037 is available in exposed pad SO-8
package.
Enable and Soft Start
The AOZ1037 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 3ms.
The 3ms soft start time is set internally.
The EN pin of the AOZ1037 is active HIGH. Connect the
EN pin to V
EN to ground will disable the AOZ1037. Do not leave it
open. The voltage on the EN pin must be above 2V to
enable the AOZ1037. When voltage on the EN pin falls
below 0.6V, the AOZ1037 is disabled. If an application
circuit requires the AOZ1037 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 (R3) should connect this pin to a
DC poer trail with maximum voltage no higher than 6V.
The AOZ1037 monitors the FB voltage: when FB pin
voltage is lower than 90% of the normal voltage, N-
channel MOSFET turns on and the Power-Good pin is
pulled low, which indicates the power is abnormal.
Steady-State Operation
Under steady-state conditions, the converter operates in
fixed frequency and Continuous-Conduction Mode
(CCM).
The AOZ1037 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. 1.1 September 2010
IN
if the enable function is not used. Pulling
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 AOZ1037 uses freewheeling NMOSFET to
realize synchronous rectification. It greatly improves the
converter efficiency and reduces power loss in the
low-side switch.
The AOZ1037 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.
Switching Frequency
The AOZ1037 switching frequency is fixed and set by an
internal oscillator. The practical switching frequency
could range from 400 kHz to 600 kHz due to device
variation.
Light Load Mode
The AOZ1037 includes is a Pulse-Skip architecture for
Light Load operation, enabling increased efficiency
during standby. Under Heavy Loads, the controller
operates in a standard Synchronous Mode using the
high-side PMOS as control FET and low-side NMOS as
synchronous rectifier NMOS. During Light Loads, the
controller automatically switches to a Non-Synchronous
mode using the high-side PMOS as control FET and the
integrated diode as freewheeling rectifier diode.
Output Voltage Programming
Output voltage can be set by feeding back the output to
the FB pin by using a resistor divider network. In the
application circuit shown in Figure 1, the resistor divider
network includes R
by picking a fixed R
R
V
1
O
with equation below:
=
0.8
×
⎛
⎜
⎝
1
+
R
------ -
R
1
2
and R
1
2
value and calculating the required
⎞
⎟
⎠
2
. Usually, a design is started
AOZ1037
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