AOZ1031AI
EZBuck™ 3A Synchronous Buck Regulator
Not Recommended For New Designs
General Description
Features
The AOZ1031A is a high efficiency, easy to use, 3A
synchronous buck regulator. The AOZ1031A works from
4.5V to 18V input voltage range, and provides up to 3A of
continuous output current with an output voltage adjustable down to 0.8V.
z 4.5V to 18V operating input voltage range
The AOZ1031A comes in a SO-8 package and is rated
over a -40°C to +85°C operating ambient temperature
range.
z Internal soft start
z Synchronous Buck: 80mΩ internal high-side switch
ig
n
z High efficiency: up to 95%
s
and 30mΩ internal low-side switch with integrated
schottky diode
es
z Output voltage adjustable to 0.8V
z 3A continuous output current
D
z Fixed 600kHz PWM operation
Replacement Part: AOZ6683CI
z Pulse skipping at light load for high efficiency over
ew
entire load range
z Cycle-by-cycle current limit
N
z Pre-bias start-up
Fo
r
z Short-circuit protection
z Thermal shutdown
z SO-8 package
om
m
en
de
d
Applications
z Point of load DC/DC converters
z LCD TV
z Set top boxes
z DVD/Blu-ray players/recorders
z Cable modems
z PCIe graphics cards
ec
z Telecom/Networking/Datacom equipment
VIN
C1
22µF
N
ot
R
Typical Application
VIN
L1 4.7µH
EN
AOZ1031
COMP
R1
RC
CC
VOUT
LX
FB
AGND
PGND
C2, C3
22µF
R2
Figure 1. 3.3V 3A Synchronous Buck Regulator
Rev. 1.6 March 2010
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Page 1 of 15
AOZ1031AI
Ordering Information
Part Number
Ambient Temperature Range
Package
Environmental
AOZ1031AI
-40°C to +85°C
SO-8
RoHS Compliant
Green Product
AOS Green Products use reduced levels of Halogens, and are also RoHS compliant.
Please visit www.aosmd.com/web/quality/rohs_compliant.jsp for additional information.
LX
VIN
2
7
LX
AGND
3
6
EN
FB
4
5
COMP
Pin Number
Pin Name
Fo
r
N
SO-8
(Top View)
es
8
D
1
ew
PGND
ig
n
s
Pin Configuration
1
PGND
Power ground. PGND needs to be electrically connected to AGND.
2
VIN
3
AGND
4
FB
5
COMP
Pin Description
de
d
Pin Function
en
Supply voltage input. When VIN rises above the UVLO threshold and EN is logic high, the
device starts up.
ec
om
m
Analog ground. AGND is the reference point for controller section. AGND needs to be
electrically connected to PGND.
EN
LX
External loop compensation pin. Connect a RC network between COMP and AGND to
compensate the control loop.
Enable pin. Pull EN to logic high to enable the device. Pull EN to logic low to disable the
device. Do not leave it open.
Switching node. PWM output connection to inductor.
N
ot
7, 8
R
6
Feedback input. The FB pin is used to set the output voltage via a resistive voltage divider
between the output and AGND.
Rev. 1.6 March 2010
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Page 2 of 15
AOZ1031AI
Block Diagram
VIN
UVLO
& POR
EN
Internal
+5V
5V LDO
Regulator
OTP
+
ISen
Softstart
Q1
ig
n
ILimit
EAmp
FB
–
–
Level
Shifter
+
FET
Driver
PWM
Control
Logic
PWM
Comp
+
600kHz
Over-Voltage
Protection
Comparator
om
m
en
de
–
0.96V
d
+
N
Frequency
Foldback
Comparator
–
0.2V
Absolute Maximum Ratings
ec
Parameter
ot
LX to AGND
R
LX to AGND
N
EN to AGND
Parameter
20V
-0.7V to VIN+0.3V
-3V for 20 nS
-0.3V to VIN+0.3V
-0.3V to 6V
COMP to AGND
-0.3V to 6V
PGND to AGND
-0.3V to +0.3V
Junction Temperature (TJ)
+150°C
Storage Temperature (TS)
-65°C to +150°C
PGND
The device is not guaranteed to operate beyond the Maximum
Operating Ratings.
Rating
FB to AGND
ESD Rating(1)
AGND
Recommend Operating Ratings
Exceeding the Absolute Maximum ratings may damage the
device.
Supply Voltage (VIN)
Q2
Fo
r
+
LX
ew
COMP
D
0.8V
es
+
+
s
–
Reference
& Bias
Rating
Supply Voltage (VIN)
4.5V to 18V
Output Voltage Range
0.8V to VIN
Ambient Temperature (TA)
-40°C to +85°C
Package Thermal Resistance
SO-8 (ΘJA)
SO-8 (ΘJC)
87°C/W
30°C/W
Package Power Dissipation (PD) @
25°C Ambient
SO-8
1.15W
2.0kV
Note:
1. Devices are inherently ESD sensitive, handling precautions are
required. Human body model rating: 1.5kΩ in series with 100pF.
Rev. 1.6 March 2010
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Page 3 of 15
AOZ1031AI
Electrical Characteristics
TA = 25°C, VIN = VEN = 12V, VOUT = 3.3V unless otherwise specified.(3)
Symbol
VIN
Parameter
Conditions
Min.
Supply Voltage
Typ.
4.5
Max.
Units
18
V
V
V
Input under-voltage lockout
threshold
VIN rising
VIN falling
4.1
3.7
IIN
Supply current (Quiescent)
IOUT = 0, VFB = 1.2V, VEN >1.2V
1.6
2.5
mA
Shutdown supply current
VEN = 0V
1
10
μA
Feedback Voltage
TA = 25°C
0.8
0.812
IOFF
VFB
0.788
0.5
ig
n
Load regulation
Line regulation
1
IFB
Feedback voltage input current
VEN
EN input threshold
VHYS
EN input hysteresis
es
Off threshold
On threshold
D
ew
Frequency
500
Maximum Duty Cycle
DMIN
Minimum Duty Cycle
Fo
r
Error amplifier voltage gain
Error amplifier transconductance
PROTECTION
Current Limit
d
VOVP
Over-Voltage Protection
om
m
Soft Start Interval
OUTPUT STAGE
0.6
V
V
mV
100
600
700
kHz
%
%
500
V/V
200
μA / V
4.0
5.0
A
Off threhsold
On threshold
960
860
mV
mV
TJ rising
TJ falling
150
100
°C
°C
2.2
ms
en
Over-temperature shutdown limit
tSS
nA
9
de
ILIM
200
100
N
fO
V
%
%
2
MODULATOR
DMAX
s
VUVLO
VIN = 12V
VIN = 5V
80
130
100
180
mΩ
mΩ
Low-side switch on-resistance
VIN = 12V
VIN = 5V
30
56
36
70
mΩ
mΩ
ec
High-side switch on-resistance
N
ot
R
Notes:
3. The device is not guaranteed to operate beyond the Maximum Operating ratings.
Rev. 1.6 March 2010
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Page 4 of 15
AOZ1031AI
Typical Performance Characteristics
Circuit of Figure 1. TA = 25°C, VIN = VEN = 12V, VOUT = 3.3V unless otherwise specified.
Light Load (DCM) Operation
D
es
ig
n
s
Full Load (CCM) Operation
1us/div
ew
1us/div
Start Up to Full Load
om
m
en
de
d
Fo
r
N
Short Circuit Protection
1ms/div
4ms/div
50% to 100% Load Transient
N
ot
R
ec
Short Circuit Recovery
10ms/div
100us/div
Rev. 1.6 March 2010
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Page 5 of 15
AOZ1031AI
Efficiency
AOZ1031AI Efficiency
90
90
80
80
70
70
30
30
20
10
10
0
0.5
1.0
1.5
2.0
2.5
s
40
20
0
ig
n
40
50
0
3.0
es
50
VO = 1.2V
VO = 1.8V
VO = 3.3V
60
0
0.5
1.0
ew
VO = 1.2V
VO = 1.8V
VO = 3.3V
VO = 5V
60
Efficiency (VIN = 5V) vs. Load Current
100
Efficiency (%)
Efficiency (%)
100
D
Efficiency (VIN = 12V) vs. Load Current
1.5
2.0
2.5
3.0
IOUT (A)
d
Fo
r
N
IOUT (A)
de
Thermal Derating
en
Thermal de-rating curves for SO-8 package part under typical input and output condition based on the evaluation board.
25°C ambient temperature and natural convection (air speed < 50LFM) unless otherwise specified.
ot
0
25
35
Output Current (IO)
3.3V Output
R
2
5
1.2V, 1.8V Output
ec
3
N
Output Current (IO)
4
1
Derating Curves at 12V Input
om
m
Derating Curves at 5V/6V Input
5
4
1.2V, 1.8V, 3.3V, 5.0V Output
3
2
1
0
45
55
65
75
85
25
Ambient Temperature (TA)
Rev. 1.6 March 2010
35
45
55
65
75
85
Ambient Temperature (TA)
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Page 6 of 15
AOZ1031AI
Comparing with regulators using freewheeling Schottky
diodes, the AOZ1031A uses freewheeling NMOSFET to
realize synchronous rectification. It greatly improves the
converter efficiency and reduces power loss in the
low-side switch.
Detailed Description
The AOZ1031A 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 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 AOZ1031A will enter the discontinuous conduction
mode at light load. Several pulses may be skipped in
between switching cycles at very light load, it further
improving light load efficiency.
s
The AOZ1031A 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 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:
ig
n
The AOZ1031A is available in SO-8 package.
Enable and Soft Start
D
es
The AOZ1031A 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 4.1V and voltage
on EN pin is HIGH. In soft start process, the output voltage is ramped to regulation voltage in typically 2.2ms.
The 2.2ms soft start time is set internally.
N
where;
VO_MAX is the maximum output voltage;,
VIN is the input voltage from 4.5V to 18V,
Fo
r
The EN pin of the AOZ1031A is active high. Connect the
EN pin to VIN if enable function is not used. Pull it to
ground will disable the AOZ1031A. Do not leave it open.
The voltage on EN pin must be above 2V to enable the
AOZ1031A. When voltage on EN pin falls below 0.6V, the
AOZ1031A is disabled. If an application circuit requires
the AOZ1031A to be disabled, an open drain or open collector circuit should be used to interface to EN pin.
ew
V O_MAX = V IN – I O × R DS ( ON )
IO is the output current from 0A to 3A, and
Steady-State Operation
en
de
d
RDS(ON) is the on resistance of internal MOSFET. The value is
between 97mΩ and 200mΩ depending on input voltage and
junction temperature.
om
m
Under steady-state conditions, the converter operates
in fixed frequency and Continuous-Conduction Mode
(CCM).
N
ot
R
ec
The AOZ1031A 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 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.
Rev. 1.6 March 2010
Switching Frequency
The AOZ1031A switching frequency is fixed and set by
an internal oscillator. The practical switching frequency
could range from 500kHz to 700kHz 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. 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.
R 1⎞
⎛
V O = 0.8 × ⎜ 1 + -------⎟
R 2⎠
⎝
Some standard value of R1, R2 and most used output
voltage values are listed in Table 1 on the next page.
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Page 7 of 15
AOZ1031AI
Table 1.
Power-On Reset (POR)
Vo (V)
R1 (kΩ)
R2 (kΩ)
0.8
1.0
open
1.2
4.99
10
1.5
10
11.5
1.8
12.7
10.2
2.5
21.5
10
3.3
31.1
10
5.0
52.3
10
A power-on reset circuit monitors the input voltage. When
the input voltage exceeds 4.1V, the converter starts operation. When input voltage falls below 3.7V, the converter
will be shut down.
Thermal Protection
ew
Input Capacitor
Fo
r
The input ripple voltage can be approximated by equation below:
om
m
en
de
d
The sensed inductor current signal is also used for over
current protection. Since the AOZ1031A employs peak
current mode control, the COMP pin voltage is proportional to the peak inductor current. The COMP pin voltage is limited to be between 0.4V and 2.5V internally.
The peak inductor current is automatically limited cycle
by cycle.
The input capacitor must be connected to the VIN pin and
PGND pin of AOZ1031A 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.
N
Protection Features
Over Current Protection (OCP)
ot
R
ec
When the output is shorted to ground under fault conditions, the inductor current decays very slow during a
switching cycle because of Vo=0V. To prevent catastrophic failure, AOZ1031A detects the duration the overcurrent condition occurs. If the over-current condition
occurs for certain period, AOZ1013A totally turns off for a
period of time, then restarts. If the fault is still there, then
the chip will be off again. The converter will initiate a soft
start once the over-current condition disappears.
N
D
The basic AOZ1031A application circuit is show in
Figure 1. Component selection is explained below.
Since the switch duty cycle can be as high as 100%, the
maximum output voltage can be set as high as the input
voltage minus the voltage drop on upper PMOS and
inductor.
The AOZ1031A has multiple protection features to prevent system circuit damage under abnormal conditions.
Application Information
es
The combination of R1 and R2 should be large enough to
avoid drawing excessive current from the output, which
will cause power loss.
ig
n
s
An internal temperature sensor monitors the junction
temperature. It shuts down the internal control circuit and
high side PMOS if the junction temperature exceeds
150°C. The regulator will restart automatically under the
control of soft-start circuit when the junction temperature
decreases to 100°C.
IO
VO ⎞ VO
⎛
ΔV IN = ----------------- × ⎜ 1 – ---------⎟ × --------f × C IN ⎝
V IN⎠ V IN
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:
VO ⎛
VO ⎞
- ⎜ 1 – --------⎟
I CIN_RMS = I O × -------V IN ⎝
V IN⎠
if we let m equal the conversion ratio:
VO
-------- = m
V IN
The relation between the input capacitor RMS current
and voltage conversion ratio is calculated and shown in
Figure 2 on the next page. 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.
Rev. 1.6 March 2010
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Page 8 of 15
AOZ1031AI
The inductor takes the highest current in a buck circuit.
The conduction loss on inductor need to be checked for
thermal and efficiency requirements.
0.5
0.4
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.
ICIN_RMS(m) 0.3
IO
0.2
Output Capacitor
0.1
ig
n
s
The output capacitor is selected based on the DC output
voltage rating, output ripple voltage specification and ripple current rating.
Figure 2. ICIN vs. Voltage Conversion Ratio
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:
Fo
r
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 current rating. Depending on the application circuits, other low ESR tantalum capacitor may also be
used. When selecting ceramic capacitors, X5R or X7R
type dielectric ceramic capacitors should be used for
their better temperature and voltage characteristics. Note
that the ripple current rating from capacitor manufactures
are based on certain amount of life time. Further
de-rating may be necessary in practical design.
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.
es
1
D
0.5
m
ew
0
N
0
1
ΔV O = ΔI L × ⎛ ESR CO + -------------------------⎞
⎝
8×f×C ⎠
de
d
O
Inductor
ec
VO ⎛
VO ⎞
-⎟
ΔI L = ----------- × ⎜ 1 – -------f×L ⎝
V IN⎠
om
m
en
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:
CO is output capacitor value, and
ESRCO is the Equivalent Series Resistor of 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:
1
ΔV O = ΔI L × ------------------------8×f×C
R
The peak inductor current is:
ΔI L
I Lpeak = I O + -------2
ot
O
N
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. Usually, peak to peak ripple current on inductor is designed to be 20%
to 30% of output current.
When selecting the inductor, make sure it is able to handle the peak current without saturation even at the highest operating temperature.
Rev. 1.6 March 2010
where;
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:
ΔV O = ΔI L × ESR CO
For lower output ripple voltage across the entire operating temperature range, X5R or X7R dielectric type of
ceramic, or other low ESR tantalum are recommended to
be used as output capacitors.
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Page 9 of 15
AOZ1031AI
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:
where;
GEA is the error amplifier transconductance, which is
200 x 10-6 A/V,
GVEA is the error amplifier voltage gain, which is 500 V/V, and
ΔI L
I CO_RMS = ---------12
C2 is compensation capacitor in Figure 1.
s
ig
n
es
f C = 40kHz
d
1
f P1 = ----------------------------------2π × C O × R L
Usually, it is recommended to set the bandwidth to be
equal or less than 1/10 of switching frequency. The
AOZ1031A operates at a frequency range from 500kHz
to 700kHz. It is recommended to choose a crossover frequency equal or less than 40kHz.
Fo
r
With peak current mode control, the buck power stage
can be simplified to be a one-pole and one-zero system
in frequency domain. The pole is dominant pole can be
calculated by:
N
The AOZ1031A employs peak current mode control for
easy use and fast transient response. Peak current mode
control eliminates the double pole effect of the output
L&C filter. It greatly simplifies the compensation loop
design.
To design the compensation circuit, a target crossover
frequency fC for close loop must be selected. The system
crossover frequency is where control loop has unity gain.
The crossover is the also called the converter bandwidth.
Generally a higher bandwidth means faster response to
load transient. However, the bandwidth should not be too
high because of system stability concern. When designing the compensation loop, converter stability under all
line and load condition must be considered.
D
Loop Compensation
1
f Z2 = ----------------------------------2π × C C × R C
ew
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.
The zero given by the external compensation network,
capacitor C2 and resistor R3, is located at:
en
om
m
1
f Z1 = -----------------------------------------------2π × C O × ESR CO
de
The zero is a ESR zero due to output capacitor and its
ESR. It is can be calculated by:
where;
The strategy for choosing RC and CC is to set the cross
over frequency with RC and set the compensator zero
with CC. Using selected crossover frequency, fC, to calculate RC:
VO
2π × C 2
R C = f C × ---------- × ----------------------------V
G ×G
CO is the output filter capacitor,
FB
RL is load resistor value, and
EA
CS
where;
The compensation design is actually to shape the converter control loop transfer function to get desired gain
and phase. Several different types of compensation network can be used for the AOZ1031A. For most cases, a
series capacitor and resistor network connected to the
COMP pin sets the pole-zero and is adequate for a stable
high-bandwidth control loop.
fC is desired crossover frequency. For best performance, fC is
set to be about 1/10 of switching frequency,
GCS is the current sense circuit transconductance, which is 6.68
A/V.
In the AOZ1031A, FB pin and COMP pin are the inverting
input and the output of internal error amplifier. A series R
and C compensation network connected to COMP provides one pole and one zero. The pole is:
The compensation capacitor CC and resistor RC together
make a zero. This zero is put somewhere close to the
dominate pole fP1 but lower than 1/5 of selected crossover frequency. CC can is selected by:
G EA
f P2 = ------------------------------------------2π × C C × G VEA
1.5
C C = ----------------------------------2π × R C × f P1
N
ot
R
ec
ESRCO is the equivalent series resistance of output capacitor.
Rev. 1.6 March 2010
VFB is 0.8V,
GEA is the error amplifier transconductance, which is
200 x 10-6 A/V, and
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Page 10 of 15
AOZ1031AI
Equation above can also be simplified to:
Please see the thermal de-rating curves for maximum
load current of the AOZ1031A under different ambient
temperature.
s
ig
n
2. Do not use thermal relief connection to the VIN and
the PGND pin. Pour a maximized copper area to the
PGND pin and the VIN pin to help thermal dissipation.
Fo
r
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 AOZ1031A.
1. The LX pins are connected to internal PFET and
NFET drains. They are low resistance thermal conduction path and most noisy switching node. Connected a large copper plane to LX pin to help thermal
dissipation.
es
In the AOZ1031A 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 low side NMOSFET. Current flows in the
second loop when the low side NMOSFET is on.
The AOZ1031A is standard SO-8 package. Several layout tips are listed below for the best electric and thermal
performance. Figure 3 on the next page illustrates a PCB
layout example of AOZ1031A.
D
Thermal Management and Layout
Consideration
ew
An easy-to-use application software which helps to
design and simulate the compensation loop can be found
at www.aosmd.com.
The thermal performance of the AOZ1031A 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.
N
CO × RL
C C = --------------------RC
4. A ground plane is preferred. If a ground plane is not
used, separate PGND from AGND and connect them
only at one point to avoid the PGND pin noise coupling to the AGND pin.
P total_loss = V IN × I IN – V O × I O
en
de
d
In the AOZ1031A buck regulator circuit, the major power
dissipating components are the AOZ1031A and the output inductor. The total power dissipation of converter circuit can be measured by input power minus output
power.
3. Input capacitor should be connected to the VIN pin
and the PGND pin as close as possible.
5. Make the current trace from LX pins to L to Co to the
PGND as short as possible.
6. Pour copper plane on all unused board area and
connect it to stable DC nodes, like VIN, GND or
VOUT.
P inductor_loss = IO2 × R inductor × 1.1
7. Keep sensitive signal trace far away form the LX
pins.
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The power dissipation of inductor can be approximately
calculated by output current and DCR of inductor.
ot
R
The actual junction temperature can be calculated with
power dissipation in the AOZ1031A and thermal impedance from junction to ambient.
N
T junction = ( P total_loss – P inductor_loss ) × Θ JA
The maximum junction temperature of AOZ1031A is
150°C, which limits the maximum load current capability.
Rev. 1.6 March 2010
www.aosmd.com
Page 11 of 15
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Fo
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AOZ1031AI
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Figure 3. AOZ1031A (SO-8) PCB layout
Rev. 1.6 March 2010
www.aosmd.com
Page 12 of 15
AOZ1031AI
Package Dimensions, SO-8L
D
Gauge Plane
Seating Plane
e
0.25
8
E1
D
h x 45°
es
ig
n
E
s
L
ew
1
θ
A1
om
m
en
de
b
d
A2 A
0.1
Fo
r
N
7° (4x)
C
ec
2.20
N
ot
1.27
R
5.74
Unit: mm
0.80
Dimensions in millimeters
Symbols
A
Min.
1.35
A1
A2
0.10
1.25
b
c
D
0.31
0.17
4.80
E1
e
E
3.80
h
L
θ
Nom.
Max.
1.65
—
1.50
—
1.75
—
4.90
0.25
5.00
0.25
1.65
0.51
3.90
4.00
1.27 BSC
5.80
6.00
6.20
0.25
—
0.50
0.40
—
1.27
0°
—
8°
Dimensions in inches
Symbols
A
Min.
0.053
Nom.
0.065
Max.
0.069
A1
A2
0.004
0.049
—
0.059
0.010
0.065
b
c
D
0.012
0.007
0.189
—
—
0.193
0.020
0.010
0.197
E1
e
E
0.150
h
L
0.010
0.016
—
—
0.020
0.050
θ
0°
—
8°
0.154 0.157
0.050 BSC
0.228 0.236 0.244
Notes:
1. All dimensions are in millimeters.
2. Dimensions are inclusive of plating
3. Package body sizes exclude mold flash and gate burrs. Mold flash at the non-lead sides should be less than 6 mils.
4. Dimension L is measured in gauge plane.
5. Controlling dimension is millimeter, converted inch dimensions are not necessarily exact.
Rev. 1.6 March 2010
www.aosmd.com
Page 13 of 15
AOZ1031AI
Tape and Reel Dimensions
SO-8 Carrier Tape
P1
D1
See Note 3
P2
T
See Note 5
E1
E2
E
A0
D0
ig
n
K0
P0
Feeding Direction
D0
1.60
±0.10
D1
1.50
±0.10
E1
1.75
±0.10
E
12.00
±0.10
P0
8.00
±0.10
E2
5.50
±0.10
P2
2.00
±0.10
P1
4.00
±0.10
T
0.25
±0.10
D
K0
2.10
±0.10
B0
5.20
±0.10
SO-8 Reel
Fo
r
W1
G
S
N
K
om
m
en
de
d
M
V
R
N
ew
A0
6.40
±0.10
es
Unit: mm
Package
SO-8
(12mm)
s
See Note 3
B0
W1
17.40
±1.00
W
K
H
10.60
ø13.00
+0.50/-0.20
S
2.00
±0.50
G
—
R
—
V
—
SO-8 Tape
R
ec
W
N
Tape Size Reel Size
M
12mm
ø330
ø330.00 ø97.00 13.00
±0.10 ±0.30
±0.50
H
N
ot
Leader/Trailer
& Orientation
Trailer Tape
300mm min. or
75 empty pockets
Rev. 1.6 March 2010
Components Tape
Orientation in Pocket
www.aosmd.com
Leader Tape
500mm min. or
125 empty pockets
Page 14 of 15
AOZ1031AI
AOZ1031 Package Marking
Z1031AI
FAYWLT
ig
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Part Number Code
es
Assembly Lot Code
Fab & Assembly Location
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Fo
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D
Year & Week Code
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LEGAL DISCLAIMER
om
m
Applications or uses as critical components in life support devices or systems are not authorized. AOS does not
assume any liability arising out of such applications or uses of its products. AOS reserves the right to make
changes to product specifications without notice. It is the responsibility of the customer to evaluate suitability of the
product for their intended application. Customer shall comply with applicable legal requirements, including all
applicable export control rules, regulations and limitations.
R
ec
AOS' products are provided subject to AOS' terms and conditions of sale which are set forth at:
http://www.aosmd.com/terms_and_conditions_of_sale
ot
LIFE SUPPORT POLICY
N
ALPHA & OMEGA SEMICONDUCTOR PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL
COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS.
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.
Rev. 1.6 March 2010
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.
www.aosmd.com
Page 15 of 15
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