Rev. 2.0 June 2015 www.aosmd.com Page 1 of 13
AOZ1282CI-1
EZBuck™ 600mA Simple Buck Regulator
General Description
The AOZ1282CI-1 is a high efficiency, simple to use,
600mA buck regulator flexible enough to be optimized for
a variety of applications. The AOZ1282CI-1 works from a
4.5V to 36V input voltage range, and provides up to
600mA of continuous output current. The output voltage
is adjustable down to 0.8V. The fixed switching frequency
of 1MHz PWM operation reduces inductor size.
Features
4.5V to 36V operating input voltage range
420m internal NMOS
Up to 95% efficiency
Internal compensation
600mA continuous output current
Fixed 1MHz 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
Industrial/power meters
Set top boxes and cable modems
DVD drives and HDDs
LCD Monitors & TVs
Telecom/Networking/Datacom equipment
Typical Application
Figure 1. 600mA Buck Regulator
VIN
EN LX
BST
GND FB
AOZ1282CI-1
L1
C4
C3
R1
R2
C2 C6
VIN
CN
C1
C7
1
EN
1
2
5
4
2
D1
C5
VOUT
1
2
1
6
3
AOZ1282CI-1
Rev. 2.0 June 2015 www.aosmd.com Page 2 of 13
Ordering Information
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
Pin Description
Part Number Ambient Temperature Range Package Environmental
AOZ1282CI-1 -40 °C to +85 °C SOT23-6L Green Product
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.
LX
VIN
EN
1
2
3
BST
GND
FB
SOT23-6L
(Top View)
6
5
4
AOZ1282CI-1
Rev. 2.0 June 2015 www.aosmd.com Page 3 of 13
Absolute Maximum Ratings
Exceeding the Absolute Maximum Ratings may damage the
device.
Note:
1. Devices are inherently ESD sensitive, handling precautions are
required. Human body model rating: 1.5kΩ in series with 100pF.
Recommended Operating Conditions
The device is not guaranteed to operate beyon d the
Recommended Operating Conditions.
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.
Parameter Rating
Supply Voltage (VIN) 40V
LX to GND -0.7V to VVIN+ 0.3V
EN to GND -0.3V to 40V
FB to GND -0.3V to 6V
BST to GND VLX + 6V
Junction Temperature (TJ) +150°C
Storage Temperature (TS) -65°C to +150°C
ESD Rating(1) 2kV
Parameter Rating
Supply Voltage (VIN) 4.5V to 36V
Output Voltage (VOUT) 0.8V to 0.85*VVIN
Ambient Temperature (TA) -40°C to +85°C
Package Thermal Resistance (ΘJA)
SOT23-6L 220°C/W
Symbol Parameter Conditions Min. Typ. Max. Units
VIN Supply Voltage 4.5 36 V
VUVLO Input Under-Voltage Lockout Threshold VIN rising
VIN falling 2.3
2.9 V
V
UVLO Hysteresis 260 mV
IIN Supply Current (Quiescent) IOUT = 0, VFB = 1V, VEN > 1.2V 11.5mA
IOFF Shutdown Supply Current VEN = 0V 8 μA
VFB Feedback Voltage TA = 25ºC 784 800 816 mV
VFB_LOAD Load Regulation 120mA < Load < 1.08A 0.5 %
VFB_LINE Line Regulation Load = 600mA 0.03 %/V
IFB Feedback Voltage Input Current VFB = 800mV 500 nA
ENABLE
VEN_OFF
VEN_ON
EN Input Threshold Off threshold
On threshold 1.2
0.4 V
V
VEN_HYS EN Input Hysteresis 200 mV
IEN Enable Input Current 3μA
MODULATOR
fOFrequency 800 1000 1200 kHz
DMAX Maximum Duty Cycle 87 %
TON_MIN Minimum On Time 150 ns
ILIM Current Limit 0.75 0.95 A
Over-Temperature Shutdown Limit TJ rising
TJ falling
150
110
°C
°C
TSS Soft Start Interval 0.6 ms
POWER STATE OUTPUT
ILEAKAGE NMOS Leakage VEN = 0V, VLX = 0V 10 μA
RDS(ON) NMOS On-Resistance VIN = 12V 420 m
AOZ1282CI-1
Rev. 2.0 June 2015 www.aosmd.com Page 4 of 13
Block Diagram
PWM
Logic
Enable
Detect SoftStart
Regulator
FB
EN
0.8V
Error
Amplifier
Driver
BST
LX
VIN
Ramp
Generator
OSC
PWM
Comparator
GND
Current
Sense
BST
LDO
OC
CLK
AOZ1282CI-1
Rev. 2.0 June 2015 www.aosmd.com Page 5 of 13
Typical Performance Characteristics
Circuit of Figure 1. TA = 25°C, VIN = 20V, VEN = 5V, VOUT = 12V, unless otherwise specified.
200µs/div
500µs/div
Start Up to Full Load Load Transient
Full Load Operation
1µs/div
1µs/div
IN ripple
Voltage
(200mV/div)
OUT ripple
Voltage
(20mV/div)
Inductor
Current
(1A/div)
LX
Voltage
(10V/div)
Light Load Operation
1ms/div
1ms/div
Short Circuit Protection Short Circuit Recovery
IN ripple
Voltage
(200mV/div
OUT ripple
Voltage
(20mV/div)
Inductor
Current
(1A/div)
LX
Voltage
(10V/div)
EN
Voltage
(5V/div)
OUT
Voltage
(5V/div)
Inductor
Current
(1A/div)
LX
Voltage
(10V/div)
OUT ripple
Voltage
(20mV/div)
Inductor
Current
(0.5A/div)
OUT
Voltage
(10V/div)
Inductor
Current
(0.5A/div)
LX
Voltage
(10V/div)
OUT
Voltage
(10V/div)
Inductor
Current
(0.5A/div)
LX
Voltage
(10V/div)
AOZ1282CI-1
Rev. 2.0 June 2015 www.aosmd.com Page 6 of 13
Typical Performance Characteristics (continued)
0.4
Efficiency (Vo=12V)
vs. Load Current
60
65
70
75
80
85
95
90
100
0.2 0.30.1
Load Current (A)
Efficiency (%)
0.600.5
Efficiency (Vo=5V)
vs. Load Current
Efficiency (%)
60
65
100
0.40.2 0.30.1 0.60.5
20V–5V
12V–5V
15V–12V
20V–12V
24V–12V
Load Current (A)
70
75
80
85
95
90
24V–5V
0
AOZ1282CI-1
Rev. 2.0 June 2015 www.aosmd.com Page 7 of 13
Detailed Description
The AOZ1282CI-1 is a current-mode step down regulator
with integrated high side NMOS switch. It operates from
a 4.5V to 36V input voltage range and supplies up to
600mA of load current. Features include enable control,
under voltage lock-out, internal soft-start, output over-
voltage protection, over-current protection and thermal
shut down.
The AOZ1282CI-1 is available in SOT23-6L package.
Enable and Soft Start
The AOZ1282CI-1 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 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 600µs. The 600µs soft start time is set
internally.
The EN pin of the AOZ1282CI-1 is active high. Connect
the EN pin to VIN if enable function is not used. Pull it to
ground will disable the AOZ1282CI-1. Do not leave it
open. The voltage on EN pin must be above 1.2 V to
enable the AOZ1282CI-1. When voltage on EN pin falls
below 0.4V, the AOZ1282CI-1 is disabled.
Steady-State Operation
Under steady-state conditions, the converter operates in
fixed frequency and Continuous-Conduction Mode
(CCM).
The AOZ1282CI-1 integrates an internal NMOS 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 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.
Switching Frequency
The AOZ1282CI-1 switching frequency is fixed and set
by an internal oscillator. The switching frequency is set
internally 1MHz.
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.
Some standard values of R1 and R2 for the most
commonly used output voltage values are listed in
Table 1.
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-1 has multiple protection features to
prevent system circuit damage under abnormal
conditions.
Over Current Protection (OCP)
The sensed inductor current signal is also used for over
current protection.
The cycle by cycle current limit threshold is set normal
value of 0.95A. 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 the current duty cycle. The inductor current
stop rising. The cycle by cycle current limit protection
directly limits inductor peak current. The average
inductor current is also limited due to the limitation on
peak inductor current. When cycle by cycle current limit
circuit is triggered, the output voltage drops as the duty
cycle decreasing.
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
VO0.8 1 R1
R2
-------
+
×=
AOZ1282CI-1
Rev. 2.0 June 2015 www.aosmd.com Page 8 of 13
The AOZ1282CI-1 has internal short circuit protection to
protect itself from catastrophic failure under output short
circuit conditions. The FB pin voltage is proportional to
the output voltage. Whenever FB pin voltage is below
0.2V, the short circuit protection circuit is triggered. As a
result, 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, the
inductor average current is greatly reduced.
Under Voltage Lock Out (UVLO)
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, the
converter will stop switching.
Thermal Protection
An internal temperature sensor monitors the junction
temperature. It shuts down the internal control circuit and
high side NMOS if the junction temperature exceeds
150ºC. The regulator will restart automatically under the
control of soft-start circuit when the junction temperature
decreases to 110°C.
Application Information
The basic AOZ1282CI-1 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-1 to maintain steady
input voltage and filter out the pulsing input current. The
voltage rating of input capacitor must be greater than
maximum input voltage plus ripple voltage.
The input ripple voltage can be approximated by
equation below:
Since the input current is discontinuous in a buck
converter, the current stress on the input capacitor is
another concern when selecting the capacitor. For a buck
circuit, the RMS value of input capacitor current can be
calculated by:
if we let m equal the conversion ratio:
The relationship between the input capacitor RMS
current and voltage conversion ratio is calculated and
shown 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.
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 the
application circuits, other low ESR tantalum capacitor or
aluminum electrolytic capacitor may also be used. When
selecting 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 is
based on certain amount of life time. Further de-rating
may be necessary for practical design requirement.
Inductor
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:
The peak inductor current is:
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.
ΔVIN IO
fC
IN
×
----------------- 1VO
VIN
---------
–
VO
VIN
---------
××=
ICIN_RMS IOVO
VIN
---------1VO
VIN
---------
–
×=
VO
VIN
---------m=
0
0.1
0.2
0.3
0.4
0.5
0 0.5 1
m
I
CIN_RMS
(m)
I
O
ΔILVO
fL×
-----------1VO
VIN
---------
–
×=
ILpeak IO
ΔIL
2
--------
+=
AOZ1282CI-1
Rev. 2.0 June 2015 www.aosmd.com Page 9 of 13
When selecting the inductor, make sure it is able to
handle the peak current without saturation even at the
highest operating temperature.
The inductor takes the highest current in a buck circuit.
The conduction loss on inductor needs to be checked for
thermal and efficiency requirements.
Surface mount inductors in different shape and styles are
available from Coilcraft, Elytone and Murata. Shielded
inductors are small and radiate less EMI noise. But they
cost more than unshielded inductors. The choice
depends on EMI requirement, price and size.
Output Capacitor
The output capacitor is selected based on the DC output
voltage rating, output ripple voltage specification and
ripple 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 be
considered for long term reliability.
Output ripple voltage specification is another important
factor for selecting the output capacitor. In a buck
converter circuit, output ripple voltage is determined by
inductor value, switching frequency, output capacitor
value and ESR. It can be calculated by the equation
below:
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 switching
frequency dominates. Output ripple is mainly caused by
capacitor value and inductor ripple current. The output
ripple voltage calculation can be simplified to:
If the impedance of ESR at switching frequency
dominates, the output ripple voltage is mainly decided by
capacitor ESR and inductor ripple current. The output
ripple voltage calculation can be further simplified to:
For lower output ripple voltage across the entire
operating temperature range, X5R or X7R dielectric type
of 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 is
decided by the peak to peak inductor ripple current.
It can be calculated by:
Usually, the ripple current rating of the output capacitor is
a smaller issue because of the low current stress. When
the buck inductor is selected to be very small and
inductor ripple current is high, output capacitor could be
overstressed.
Schottky Diode Selection
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 and
recovery of diode, Schottky diode is recommended to
use. The maximum reverse voltage rating of the chosen
Schottky diode should be greater than the maximum
input voltage, and the current rating should be greater
than the maximum load current.
Thermal Management and Layout
Consideration
In the AOZ1282CI-1 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 and
load, and then return to the input capacitor through
ground. Current flows in the first loop when the high side
switch 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 the
noise of this circuit and improves efficiency. A ground
plane is strongly recommended to connect input
capacitor, output capacitor, and PGND pin of the
AOZ1282CI-1.
In the AOZ1282CI-1 buck regulator circuit, the major
power dissipating components are the AOZ1282CI-1, the
Schottky diode and output inductor. The total power
dissipation of converter circuit can be measured by input
power minus output power.
ΔVOΔILESRCO 1
8fC
O
××
-------------------------
+
×=
ΔVOΔIL1
8fC
O
××
-------------------------
×=
ΔVOΔILESRCO
×=
ICO_RMS
ΔIL
12
----------
=
Ptotal_loss VIN IIN
×()VOVIN
×()–=
AOZ1282CI-1
Rev. 2.0 June 2015 www.aosmd.com Page 10 of 13
The power dissipation in Schottky can be approximated
as:
where,
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.
The actual junction temperature can be calculated with
power dissipation in the AOZ1282CI-1 and thermal
impedance from junction to ambient.
The maximum junction temperature of AOZ1282CI-1 is
150ºC, which limits the maximum load current capability.
The thermal performance of the AOZ1282CI-1 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.
Several layout tips are listed below for the best electric
and thermal performance.
1. The input capacitor should be connected as close as
possible to the VIN pin and the GND pin.
2. The inductor should be placed as close as possible
to the LX pin and the output capacitor.
3. Keep the connection of the schottky diode between
the LX pin and the GND pin as short and wide
as possible.
4. Place the feedback resistors and compensation
components as close to the chip as possible.
5. Keep sensitive signal traces away from the LX pin.
6. Pour a maximized copper area to the VIN pin, the
LX pin and especially the GND pin to help thermal
dissipation.
7. Pour a copper plane on all unused board area and
connect the plane to stable DC nodes, like VIN,
GND or VOUT.
Pdiode_loss IO1D–()VFW_Schottky
××=
Pinductor_loss IO2Rinductor 1.1××=
Tjunction Ptotal_loss Pdiode_loss
–Pinductor_loss
–()
θJA T+ambient
--------------------------------------------------------------------------------------------------------------------------
=
AOZ1282CI-1
Rev. 2.0 June 2015 www.aosmd.com Page 11 of 13
Package Dimensions, SOT23-6
E1
E
AA2
A1
e
e1
D
.010mm
0.80
0.95 0.63
2.40
b
L
c
Gauge Plane Seating Plane
0.25mm
θ1
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.
Symbols
A
A1
A2
b
c
D
E
E1
e
e1
L
θ1
Dimensions in millimeters
Min.
0.80
0.00
0.70
0.30
0.08
2.70
2.50
1.50
0.30
0°
Nom.
—
—
1.10
0.40
0.13
2.90
2.80
1.60
0.95 BSC
1.90 BSC
—
—
Max.
1.25
0.15
1.20
0.50
0.20
3.10
3.10
1.70
0.60
8°
Symbols
A
A1
A2
b
c
D
E
E1
e
e1
L
θ1
Min.
0.031
0.000
0.028
0.012
0.003
0.106
0.098
0.059
0.012
0°
Nom.
—
—
0.043
0.016
0.005
0.114
0.110
0.063
0.037 BSC
0.075 BSC
—
—
Max.
0.049
0.006
0.047
0.020
0.008
0.122
0.122
0.067
0.024
8°
Dimensions in inches
UNIT: mm
RECOMMENDED LAND PATTERN
AOZ1282CI-1
Rev. 2.0 June 2015 www.aosmd.com Page 12 of 13
Tape and Reel Dimensions, SOT23-6
Tape
Reel
Leader/Trailer and Orientation
Trailer Tape
300mm min. or
75 Empty Pockets
Components Tape
Orientation in Pocket
Leader Tape
500mm min. or
125 Empty Pockets
Unit: mm
Unit: mm
G
V
Feeding Direction
Tape Size
8 mm
Reel Size
ø180
M
ø180.00
±0.50
N
ø60.50
Min.
W1
11.40
±1.0
W
9.00
±0.30
Package
SOT-23
A0
3.15
±0.10
B0
3.27
±0.10
K0
1.34
±0.10
D0
1.10
±0.01
D1
1.50
±0.10
E
8.00
±0.20
E1
1.75
±0.10
E2
3.50
±0.05
P0
4.00
±0.10
P1
4.00
±0.10
P2
2.00
±0.10
T
0.25
±0.05
H
ø13.00
+0.50 / -0.20
K
10.60
S
2.00
±0.50
G
ø9.00
R
5.00
T
K0
B0
D1
A0 D0
P2
P1
P0
E1
E2 E
V
18.00
R
W1
N
W
M
S
K
H
AOZ1282CI-1
Rev. 2.0 June 2015 www.aosmd.com Page 13 of 13
Part Marking
AOZ1282CI-1
(SOT23-6)
2DBN1W
LT
Week & Year Code
Part Number Code
Option / Assembly Location Code
Assembly Lot Code
As used herein:
1. Life support devices or systems are devices or
systems 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 accordance
with instructions for use provided in the labeling, can be
reasonably expected to result in a significant injury of
the user.
2. A critical component in any component of a life
support, device, or system whose failure to perform can
be reasonably expected to cause the failure of the life
support device or system, or to affect its safety or
effectiveness.
LEGAL DISCLAIMER
Alpha and Omega Semiconductor makes no representations or warranties with respect to the accuracy or
completeness of the information provided herein and takes no liabilities for the consequences of use of such
information 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 POLICY
ALPHA AND OMEGA SEMICONDUCTOR PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL
COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS.
