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AOZ1014

5A Simple Buck Regulator

Alpha and 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 VIN if enable function is not used. Pull it to

ground will disable the AOZ1014. Do not leave it open.

The voltage on EN pin must be above 2.0 V to enable

the AOZ1014. When voltage on EN pin falls below 0.6 V,

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 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.

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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 regulation 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:

VO _ MAX = VIN − IO × (RDS (ON ) + Rinductor )

Where VO_MAX is the maximum output voltage;

VIN is the input voltage from 4.5V to 16V;

IO is the output current from 0A to 5A;

RDS(ON) is the on resistance of internal

MOSFET, the value is between 25mΩ and

55mΩ depending on input voltage and junction

temperature;

Rinductor is the inductor DC resistance;

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 R1 and R2. Usually, a design is started

by picking a fixed R2 value and calculating the required

R1 with equation below.

VO

=

0.8 × (1 +

R1

R2

)

Some standard value of R1, R2 for most commonly used

output voltage values are listed in Table 1.

Table 1.

Vo (V)

0.8

1.2

1.5

1.8

2.5

3.3

5.0

R1 (kΩ)

1.0

4.99

10

12.7

21.5

31.6

52.3

R2 (kΩ)

open

10

11.5

10.2

10

10

10

Combination of R1 and R2 should be large enough to

avoid drawing excessive current from the output, which

will cause power loss.

February 2006

www.aosmd.com

Page 9 of 21

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