AOZ1282CI
EZBuck™ 1.2A Simple Buck Regulator

General Description

Features

The AOZ1282CI is a high efficiency, simple to use, 1.2A
buck regulator flexible enough to be optimized for avariety of applications. The AOZ1282CI works from a
4.5V to 36V input voltage range, and provides up to 1.2Aof continuous output current. The output voltage isadjustable down to 0.8V. The fixed switching frequencyof 450kHz PWM operation reduces inductor size.

 4.5V to 36V operating input voltage range
 420mΩ internal NMOS Up to 95% efficiency
 Internal compensation
 1.2A continuous output current
 Fixed 450kHz PWM operation
 Internal soft start Output voltage adjustable down to 0.8V
 Cycle-by-cycle current limit Short-circuit protection
 Thermal shutdown
 Small size SOT23-6L

Applications
 Point of load DC/DC conversion
 Set top boxes and cable modems
 DVD drives and HDDs
 LCD Monitors & TVs
 Telecom/Networking/Datacom equipment

Typical Application
VIN
C3
C1
4.7µF
VIN

BS

EN

L1

AOZ1282CI

LX

VOUT

22µH
R1

GND

C2
10µF

FB

R2

Figure 1. 1.2A Buck Regulator

Rev. 1.2 March 2016www.aosmd.com

Page 1 of 13

AOZ1282CI
Ordering Information
Part Number

Ambient Temperature Range

Package

Environmental

AOZ1282CI-40 °C to +85 °C

SOT23-6L

Green Product

AOS Green Products use reduced levels of Halogens, and are also RoHS compliant.
Please visit www.aosmd.com/media/AOSGreenPolicy.pdf for additional information.

Pin Configuration
BST 1

6

LX

GND 2

5

VIN

FB 3

4

EN

SOT23-6L(Top View)

Pin Description
Pin Number

Pin Name

Pin Function

1

BST

Bootstrap Voltage Input. High side driver supply. Connected to 100nF capacitor between
BST and LX.

2

GND

Ground.

3

FB

Feedback Input. It is regulated to 0.8V. The FB pin is used to determine the PWM output
voltage via a resistor divider between the output and GND.

4

EN

Enable Pin. The enable pin is active high. Connect EN pin to VIN through current limiting
resistor. Do not leave the EN pin floating.

5

VIN

Supply Voltage Input. Range from 4.5V to 36V. When VIN rises above the UVLO
threshold the device starts up.

6

LX

PWM Output. Connect to inductor.

Rev. 1.2 March 2016www.aosmd.com

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AOZ1282CI
Absolute Maximum Ratings

Recommended Operating Conditions

Exceeding the Absolute Maximum Ratings may damage thedevice.

The device is not guaranteed to operate beyond the
Recommended Operating Conditions.

Parameter

RatingSupply Voltage (VIN)

Parameter
40V

RatingSupply Voltage (VIN)

4.5V to 36V

Output Voltage (VOUT)

0.8V to VVIN

LX to GND

-0.7V to VVIN+ 0.3V

EN to GND

-0.3V to 40V

Ambient Temperature (TA)FB to GND

-0.3V to 6V

BST to GND

VLX + 6V

Package Thermal Resistance (ΘJA)
SOT23-6L

Junction Temperature (TJ)

+150°C

Storage Temperature (TS)-65°C to +150°C

ESD Rating(1)-40°C to +85°C
220°C/W

2kV

Note:
1. Devices are inherently ESD sensitive, handling precautions are
required. Human body model rating: 1.5kΩ in series with 100pF.

Electrical Characteristics
TA = 25 °C, VIN = VEN = 12V, unless otherwise specified. Specifications in BOLD indicate a temperature range of -40°C to +85°C.
These specifications are guaranteed by design.

SymbolParameter

VIN

Supply Voltage

VUVLO

Input Under-Voltage Lockout Threshold

Conditions

Min.
4.5

VIN rising
VIN falling

Max.

Units

36

V

2.9

V
V

2.3

UVLO Hysteresis

260

IIN

Supply Current (Quiescent)

IOUT = 0, VFB = 1V, VEN > 1.2V

IOFF

Shutdown Supply Current

VEN = 0V

VFB

Feedback Voltage

TA = 25ºC

VFB_LOAD Load Regulation

Typ.

1
784

800

mV
1.5

mA

8

μA

816

mV

120mA < Load < 1.08A

0.5%Line Regulation

Load = 600mA

0.03

%/V

Feedback Voltage Input Current

VFB = 800mV

500

nA

VEN_OFFVEN_ONEN Input Threshold

Off threshold
On threshold

VEN_HYSEN Input Hysteresis

IEN

Enable Input Current

VFB_LINEIFB
ENABLE

0.4
1.2
200

V
V
mV

3

μA

540

kHz

MODULATOR
fO

Frequency

DMAX

Maximum Duty Cycle

TON_MIN

Minimum On Time

ILIM

Current Limit
Over-Temperature Shutdown Limit

TSS

360

1.5
TJ rising
TJ falling

Soft Start Interval

450
87

%

150

ns

1.9

A

150
110

°C
°C

1.5

ms

POWER STATE OUTPUTILEAKAGE

NMOS Leakage

VEN = 0V, VLX = 0V

RDS(ON)NMOS On-Resistance

VIN = 12V

Rev. 1.2 March 2016www.aosmd.com

10
420

μA
mΩ

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AOZ1282CI
Block Diagram
VIN

Regulator

EN

EnableDetectCurrent
Sense

SoftStart
Ramp
Generator

OSC

BST
LDO

OC
CLK

FB

Driver

PWM
Logic

0.8V

Error
Amplifier

BST

LX

PWM
Comparator

GND

Rev. 1.2 March 2016www.aosmd.com

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AOZ1282CI
Typical Performance Characteristics
Circuit of Figure 1. TA = 25°C, VIN = VEN = 12V, VOUT = 3.3 V, unless otherwise specified.

Full Load Operation

Light Load OperationIN
Voltage(500mV/div)

IN
Voltage(1V/div)

OUT
Voltage(100mV/div)

OUT
Voltage(100mV/div

LX
Voltage(10V/div)

LX
Voltage(10V/div)

LOAD
Current(1A/div)

LOAD
Current(1A/div)

2µs/div

2µs/div

Start Up to Full Load

Load TransientIN
Voltage(5V/div)
OUT
Voltage(100mV/div

OUT
Current(1A/div)
OUT
Voltage(2V/div)

OUT
Current(1A/div)

5ms/div

200µs/div

Short Circuit Protection

Short Circuit Recovery

LX
Voltage(10V/div)

LX
Voltage(10V/div)

OUT
Voltage(2V/div)

OUT
Voltage(2V/div)

LOAD
Current(1A/div)

2ms/div

2ms/div

Rev. 1.2 March 2016

LOAD
Current(1A/div)

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AOZ1282CI
Typical Performance Characteristics (continued)
Efficiency (Vo=5V)
vs. Load Current

Efficiency (Vo=3.3V)
vs. Load Current

95

95
5V–3.3V

90

90

85

85
24V–5V80

Efficiency (%)

Efficiency (%)

12V–5V

18V–5V

75
70
65

80
75
18V–3.3V

65
60

55

55

0

0.2

0.4
0.6
0.8
Load Current (A)

1.0

1.2

24V–3.3V

70

60

50

12V–3.3V

50

0

0.2

0.4
0.6
0.8
Load Current (A)

1.0

1.2

Current Limit vs. Input Voltage(Vo=3.3V)
2.0

Current Limit (A)

1.8
1.6
1.4
1.2
1.0
0.8
0.6

5

9

Rev. 1.2 March 2016

13

17
21
25
29
Input Voltage (V)3337

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AOZ1282CI
Detailed Description
The AOZ1282CI is a current-mode step down regulator
with integrated high side NMOS switch. It operates froma 4.5V to 36V input voltage range and supplies up to
1.2A of load current. Features include enable control,
under voltage lock-out, internal soft-start, output overvoltage protection, over-current protection and thermal
shut down.
The AOZ1282CI is available in SOT23-6L package.
Enable and Soft Start
The AOZ1282CI has internal soft start feature to limit inrush current and ensure the output voltage ramps up
smoothly to regulation voltage. A soft start process
begins when the input voltage rises to the voltage higher
than UVLO and voltage on EN pin is HIGH. In soft start
process, the output voltage is ramped to regulation
voltage in typically 400µs. The 400µs soft start time is set
internally.
The EN pin of the AOZ1282CI is active high. Connect the
EN pin to VIN if enable function is not used. Pull it toground will disable the AOZ1282CI. Do not leave it open.
The voltage on EN pin must be above 1.2 V to enable the
AOZ1282CI. When voltage on EN pin falls below 0.4V,
the AOZ1282CI is disabled.

Switching Frequency
The AOZ1282CI switching frequency is fixed and set by
an internal oscillator. The switching frequency is set
internally 450kHz.
Output Voltage Programming
Output voltage can be set by feeding back the output tothe FB pin with a resistor divider network. In theapplication 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.

R 1
V O = 0.8 ×  1 + -------
R 2Some standard values of R1 and R2 for the mostcommonly used output voltage values are listed inTable 1.
Vo (V)

R1 (kΩ)

R2 (kΩ)

1.8

80.6

64.2

2.5

49.9

23.4

3.3

49.9

15.8

5.0

49.9

9.53

Steady-State Operation
Under steady-state conditions, the converter operates in
fixed frequency and Continuous-Conduction Mode
(CCM).
The AOZ1282CI integrates an internal NMOS as thehigh-side switch. Inductor current is sensed by amplifying
the voltage drop across the drain to source of the highside power MOSFET. Output voltage is divided down by
the external voltage divider at the FB pin. The differenceof the FB pin voltage and reference is amplified by theinternal transconductance error amplifier. The error
voltage is compared against the current signal, which issum of inductor current signal and ramp compensation
signal, at PWM comparator input. If the current signal isless than the error voltage, the internal high-side switch
is on. The inductor current flows from the input throughthe 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.

Rev. 1.2 March 2016

Table 1.

The combination of R1 and R2 should be large enough to
avoid drawing excessive current from the output, which
will cause power loss.

Protection Features
The AOZ1282CI has multiple protection features toprevent system circuit damage under abnormal
conditions.
Over Current Protection (OCP)
The sensed inductor current signal is also used for overcurrent protection.
The cycle by cycle current limit threshold is set normal
value of 1.9A. When the load current reaches the current
limit threshold, the cycle by cycle current limit circuit turns
off the high side switch immediately to terminate thecurrent duty cycle. The inductor current stop rising. The
cycle by cycle current limit protection directly limits
inductor peak current. The average inductor current isalso limited due to the limitation on peak inductor current.
When cycle by cycle current limit circuit is triggered, theoutput voltage drops as the duty cycle decreasing.

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AOZ1282CI
The AOZ1282CI has internal short circuit protection toprotect itself from catastrophic failure under output shortcircuit conditions. The FB pin voltage is proportional tothe output voltage. Whenever FB pin voltage is below
0.2V, the short circuit protection circuit is triggered. As aresult, the converter is shut down and hiccups. The
converter will start up via a soft start once the short circuit
condition disappears. In short circuit protection mode, theinductor average current is greatly reduced.

The relationship between the input capacitor RMS
current and voltage conversion ratio is calculated andshown in Figure 2. It can be seen that when VO is half of
VIN, CIN is under the worst current stress. The worst
current stress on CIN is 0.5 x IO.

Under Voltage Lock Out (UVLO)

ICIN_RMS(m) 0.3
IO
0.2

An UVLO circuit monitors the input voltage. When the
input voltage exceeds 2.9V, the converter starts
operation. When input voltage falls below 2.3V, theconverter will stop switching.

0.5
0.4

0.1

Thermal Protection

0

An internal temperature sensor monitors the junction
temperature. It shuts down the internal control circuit andhigh side NMOS if the junction temperature exceeds
150ºC. The regulator will restart automatically under thecontrol of soft-start circuit when the junction temperature
decreases to 110°C.

Application Information
The basic AOZ1282CI application circuit is shown in
Figure 1. Component selection is explained below.
Input Capacitor
The input capacitor must be connected to the VIN pin
and PGND pin of the AOZ1282CI to maintain steady
input voltage and filter out the pulsing input current. The
voltage rating of input capacitor must be greater thanmaximum input voltage plus ripple voltage.

Since the input current is discontinuous in a buckconverter, the current stress on the input capacitor isanother concern when selecting the capacitor. For a buckcircuit, the RMS value of input capacitor current can becalculated by:VO-------- = m
V IN
Rev. 1.2 March 2016

1

Figure 2. ICIN vs. Voltage Conversion Ratio

For reliable operation and best performance, the input
capacitors must have current rating higher than ICIN-RMS
at worst operating conditions. Ceramic capacitors are
preferred for input capacitors because of their low ESR
and high ripple current rating. Depending on theapplication circuits, other low ESR tantalum capacitor or
aluminum electrolytic capacitor may also be used. Whenselecting ceramic capacitors, X5R or X7R type dielectric
ceramic capacitors are preferred for their better
temperature and voltage characteristics. Note that the
ripple current rating from capacitor manufactures isbased on certain amount of life time. Further de-rating
may be necessary for practical design requirement.

The inductor is used to supply constant current to output
when it is driven by a switching voltage. For given input
and output voltage, inductance and switching frequency
together decide the inductor ripple current, which is:VO  VOIOΔV IN = ----------------- ×  1 – --------- × --------f × C IN 
V IN V IN

if we let m equal the conversion ratio:

0.5m

Inductor

The input ripple voltage can be approximated byequation below:

VO 
VO 
-  1 – --------
I CIN_RMS = I O × -------V IN 
V IN

0

VO 
VO 
-
ΔI L = ----------- ×  1 – -------f×L 
V INThe peak inductor current is:

ΔI L
I Lpeak = I O + -------2
High inductance gives low inductor ripple current but
requires larger size inductor to avoid saturation. Low
ripple current reduces inductor core losses. It also
reduces RMS current through inductor and switches,
which results in less conduction loss.

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AOZ1282CI
When selecting the inductor, make sure it is able tohandle the peak current without saturation even at thehighest operating temperature.
The inductor takes the highest current in a buck circuit.
The conduction loss on inductor needs to be checked forthermal and efficiency requirements.
Surface mount inductors in different shape and styles areavailable from Coilcraft, Elytone and Murata. Shielded
inductors are small and radiate less EMI noise. But they
cost more than unshielded inductors. The choicedepends on EMI requirement, price and size.
Output Capacitor
The output capacitor is selected based on the DC output
voltage rating, output ripple voltage specification andripple current rating.
The selected output capacitor must have a higher rated
voltage specification than the maximum desired output
voltage including ripple. De-rating needs to beconsidered for long term reliability.

For lower output ripple voltage across the entire
operating temperature range, X5R or X7R dielectric typeof ceramic, or other low ESR tantalum capacitor or
aluminum electrolytic capacitor may also be used as
output capacitors.
In a buck converter, output capacitor current is
continuous. The RMS current of output capacitor isdecided by the peak to peak inductor ripple current.
It can be calculated by:

ΔI L
I CO_RMS = ---------12
Usually, the ripple current rating of the output capacitor isa smaller issue because of the low current stress. Whenthe buck inductor is selected to be very small andinductor ripple current is high, output capacitor could beoverstressed.
Schottky Diode Selection

Output ripple voltage specification is another importantfactor for selecting the output capacitor. In a buckconverter circuit, output ripple voltage is determined byinductor value, switching frequency, output capacitor
value and ESR. It can be calculated by the equation
below:The external freewheeling diode supplies the current to
the inductor when the high side NMOS switch is off. To
reduce the losses due to the forward voltage drop andrecovery of diode, Schottky diode is recommended touse. The maximum reverse voltage rating of the chosen
Schottky diode should be greater than the maximum
input voltage, and the current rating should be greaterthan the maximum load current.

1
ΔV O = ΔI L ×  ESR CO + -------------------------
8×f×C Thermal Management and Layout
ConsiderationO

where,
CO is output capacitor value, and
ESRCO is the equivalent series resistance of the output
capacitor.
When low ESR ceramic capacitor is used as output
capacitor, the impedance of the capacitor at the switchingfrequency dominates. Output ripple is mainly caused bycapacitor value and inductor ripple current. The output
ripple voltage calculation can be simplified to:1
ΔV O = ΔI L ×  -------------------------8 × f × C OIf the impedance of ESR at switching frequency
dominates, the output ripple voltage is mainly decided bycapacitor ESR and inductor ripple current. The output
ripple voltage calculation can be further simplified to:

ΔV O = ΔI L × ESR CO

In the AOZ1282CI buck regulator circuit, high pulsing
current flows through two circuit loops. The first loop
starts from the input capacitors, to the VIN pin, to the LX
pins, to the filter inductor, to the output capacitor andload, and then return to the input capacitor throughground. Current flows in the first loop when the high sideswitch is on. The second loop starts from inductor, to the
output capacitors and load, to the anode of Schottky
diode, to the cathode of Schottky diode. Current flows in
the second loop when the low side diode is on.
In PCB layout, minimizing the two loops area reduces thenoise of this circuit and improves efficiency. A groundplane is strongly recommended to connect input
capacitor, output capacitor, and PGND pin of the
AOZ1282CI.
In the AOZ1282CI buck regulator circuit, the major power
dissipating components are the AOZ1282CI, theSchottky diode and output inductor. The total power
dissipation of converter circuit can be measured by input
power minus output power.

P total_loss = ( V IN × I IN ) – ( V O × V IN )Rev. 1.2 March 2016www.aosmd.com

Page 9 of 13

AOZ1282CI
The power dissipation in Schottky can be approximatedas:Several layout tips are listed below for the best electricand thermal performance.

P diode_loss = I O × ( 1 – D ) × V FW_Schottky

1. The input capacitor should be connected as close as
possible to the VIN pin and the GND pin.

where,

2. The inductor should be placed as close as possible
to the LX pin and the output capacitor.

VFW_Schottky is the Schottky diode forward voltage drop.
The power dissipation of inductor can be approximately
calculated by output current and DCR of inductor.

3. Keep the connection of the schottky diode between
the LX pin and the GND pin as short and wide
as possible.

P inductor_loss = IO2 × R inductor × 1.1

4. Place the feedback resistors and compensation
components as close to the chip as possible.

The actual junction temperature can be calculated withpower dissipation in the AOZ1282CI and thermal
impedance from junction to ambient.

5. Keep sensitive signal traces away from the LX pin.

T

(P
–P
–P
)
total_loss diode_loss inductor_loss= -------------------------------------------------------------------------------------------------------------------------junctionθ+TJA
ambient

6. Pour a maximized copper area to the VIN pin, theLX pin and especially the GND pin to help thermal
dissipation.
7. Pour a copper plane on all unused board area andconnect the plane to stable DC nodes, like VIN,
GND or VOUT.

The maximum junction temperature of AOZ1282CI is
150ºC, which limits the maximum load current capability.
The thermal performance of the AOZ1282CI is strongly
affected by the PCB layout. Extra care should be taken
by users during design process to ensure that the IC will
operate under the recommended environmental
conditions.

Rev. 1.2 March 2016www.aosmd.com

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AOZ1282CI
Package Dimensions, SOT23-6
Gauge PlaneD
e1

Seating Plane
0.25mm

c
L

E E1

θ1
e

b

A2

A

.010mmA1

Dimensions in millimeters
RECOMMENDED LAND PATTERN

2.40
0.80
0.95

0.63
UNIT: mm

Symbols
A
A1
A2
b
c
D
E
E1
e
e1
L

Min.
0.80
0.00
0.70
0.30
0.08
2.70
2.50
1.50

Nom. Max.
—
1.25
—
0.15
1.10
1.20
0.40
0.50
0.13
0.20
2.90
3.10
2.80
3.10
1.60
1.70
0.95 BSC
1.90 BSC
0.30
—
0.60

θ1

0°

—

8°

Dimensions in inches
Symbols
A
A1
A2
b
c
D
E
E1
e
e1
L

Min.
0.031
0.000
0.028
0.012
0.003
0.106
0.098
0.059

Nom. Max.
—
0.049
—
0.006
0.043 0.047
0.016 0.020
0.005 0.008
0.114 0.122
0.110 0.122
0.063 0.067
0.037 BSC
0.075 BSC
0.012
—
0.024

θ1

0°

—

8°

Notes:
1. Package body sizes exclude mold flash and gate burrs. Mold flash at the non-lead sides should be less than 5 mils each.
2. Dimension “L” is measured in gauge plane.
3. Tolerance ±0.100 mm (4 mil) unless otherwise specified.
4. Followed from JEDEC MO-178C & MO-193C.
5. Controlling dimension is millimeter. Converted inch dimensions are not necessarily exact.

Rev. 1.2 March 2016www.aosmd.com

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AOZ1282CI
Tape and Reel Dimensions, SOT23-6
Tape
P1
D1

T

P2
E1
E2

E

B0
K0

D0

A0

P0

Feeding Direction

Unit: mm
Package

A0

B0

K0

D0

D1

E

E1

E2

P0

P1

P2

T

SOT-23

3.15
±0.10

3.27
±0.10

1.34
±0.10

1.10
±0.01

1.50
±0.10

8.00
±0.20

1.75
±0.10

3.50
±0.05

4.00
±0.10

4.00
±0.10

2.00
±0.10

0.25
±0.05

Reel

W1

S
G
N

M

K

V
R
H
W

Unit: mmTape Size

Reel Size

M

N

W

W1

8 mm

ø180

ø180.00±0.50

ø60.50
Min.

9.00
±0.30

11.40
±1.0

H

K

S

ø13.0010.60 2.00
+0.50 / -0.20
±0.50

G
ø9.00

R

V

5.00 18.00

Leader/Trailer and Orientation

Trailer Tape
300mm min. or
75 Empty Pockets

Rev. 1.2 March 2016

Components Tape
Orientation in Pocket

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Leader Tape
500mm min. or
125 Empty Pockets

Page 12 of 13

AOZ1282CI
Part Marking

B N 2D
0W

Part Number Code11

AOZ1282CI(SOT23-6)

Assembly Lot CodeWeek & Year Code

Option / Assembly Location CodeLEGAL DISCLAIMER
Alpha and Omega Semiconductor makes no representations or warranties with respect to the accuracy orcompleteness of the information provided herein and takes no liabilities for the consequences of use of suchinformation or any product described herein. Alpha and Omega Semiconductor reserves the right to make changes
to such information at any time without further notice. This document does not constitute the grant of any intellectual
property rights or representation of non-infringement of any third party’s intellectual property rights.
LIFE SUPPORT POLICYALPHA AND OMEGA SEMICONDUCTOR PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICALCOMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS.
As used herein:
1. Life support devices or systems are devices orsystems which, (a) are intended for surgical implant into
the body or (b) support or sustain life, and (c) whose
failure to perform when properly used in accordancewith instructions for use provided in the labeling, can bereasonably expected to result in a significant injury of
the user.

Rev. 1.2 March 2016

2. A critical component in any component of a life
support, device, or system whose failure to perform canbe reasonably expected to cause the failure of the life
support device or system, or to affect its safety oreffectiveness.

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