Rev. 1.1 June 2012
www.aosmd.com
Page 1 of 17
AOZ1231-01
28V/4A Synchronous EZBuck
TM
Regulator
General Description
The AOZ1231-01 is high-efficiency, easy-to-use DC/DC
synchronous buck regulator that operates up to 28V.
The device is capable of supplying 4A of continuous
output current with an output voltage adjustable down to
0.8V (±1.0%).
The AOZ1231-01 integrates an internal linear regulator
to generate 5.3V VCC from the input source. If the input
voltage is lower than 5.3V, the linear regulator operates
in low drop-output mode and the VCC voltage is equal to
input voltage minus the drop-output voltage of the
internal linear regulator.
A proprietary constant on-time PWM control with input
feed-forward results in ultra-fast transient response while
maintaining relatively constant switching frequency over
the entire input voltage range. The switching frequency
can be externally set up to 1MHz.
The devices feature multiple protection functions such
as VCC under-voltage lockout, cycle-by-current limit,
output over-voltage protection, short-circuit protection,
and thermal shutdown.
The AOZ1231-01 is available in a 5mm × 5mm
QFN-30L package and is rated over a -40°C to +85°C
ambient temperature range.
Features
Wide input voltage range:
– 4.5V to 28V (internal VCC)
– 2.7V to 28V (external VCC)
4A continuous output current
Output voltage adjustable to 0.8V (±1.0%)
Low RDS(ON) internal NFETs
– 40m high-side
– 25m low-side
Constant On-time with input feed-forward
Programmable frequency up to 1MHz
Internal 5.3V, 20mA linear regulator
Ceramic capacitor stable
Adjustable soft start
Power Good output
Over voltage protection
Integrated bootstrap diode
Cycle-by-cycle current limit
Short-circuit protection
Thermal shutdown
Thermally enhanced 5mm × 5mm QFN-30L package
Applications
Portable computers
Compact desktop PCs
Servers
Graphics cards
Set top boxes
LCD TVs
Cable modems
Point of load DC/DC converters
Telecom/Networking/Datacom equipment
AOZ1231-01
Rev. 1.1 June 2012
www.aosmd.com
Page 2 of 17
Typical Application for V
IN
= 12V or above
Typical Application for V
IN
= 5V
AOZ1231-01
Input = 12V or above
Output
1.05V, 4A
C3
100μF
R1
R3
100kΩ
R2
C2
22μF
C5
0.1μF
IN
AIN TON
Analog Ground
Power Ground
Power Good
Off On
VCC
PGOOD
EN
SS
C
SS
R
TON
C4
1μF
BST
LX
FB
AGND
PGND
L1 2.2μH
AOZ1231-01
Input = 5V
Output
1.05V, 4A
C3
100μF
R1
R3
100kΩ
R2
C2
22μF
C5
0.1μF
IN
AIN TON
Analog Ground
Power Ground
Power Good
Off On
VCC
PGOOD
EN
SS
C
SS
R
TON
C4
1μF
BST
LX
FB
AGND
PGND
L1 2.2μH
AOZ1231-01
Rev. 1.1 June 2012
www.aosmd.com
Page 3 of 17
Typical Application for High Light Load Efficiency Requirement or V
IN
= 3.3V
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.
Part Number Ambient Temperature Range Package Environmental
AOZ1231QI-01 -40°C to +85°C 30-Pin 5mm x 5mm QFN Green Product
Output
1.05V, 4A
AOZ1231-01
Input
C3
100μF
R1
R3
100kΩ
R2
C2
22μF
C5
0.1μF
IN
AIN TON
Analog Ground
Power Ground
Power Good
5V
Off On
VCC
PGOOD
EN
PFM
SS
C
SS
R
TON
C4
1μF
BST
LX
FB
AGND
PGND
L1 2.2μH
AOZ1231-01
Rev. 1.1 June 2012
www.aosmd.com
Page 4 of 17
Pin Configuration
Pin Description
1
30 29 28 27 26 25 24 23
8 9 10 11 12 13 14
2
3
4
5
6
7
PGOOD
IN
IN
IN
IN
PGND
PGND
PGND
SS
AGND
VCC
BST
PGND
LX
LX
LX
EN
PFM
AGND
FB
TON
AIN
30-pin 5mm x 5mm QFN
(Top View)
22
21
20
18
17
16
15
LX
LX
LX
PGND
PGND
PGND
PGND
PGND
LX
IN
AGND
19
Pin Number Pin Name Pin Function
1 PGOOD
Power Good Signal Output. PGOOD is an open-drain output used to indicate the status
of the output voltage. It is internally pulled low when the output voltage is 10% lower than
the nominal regulation voltage for 50µs (typical time) or 15% higher than the nominal
regulation voltage. PGOOD is pulled low during soft-start and shut down.
2EN
Enable Input. The AOZ1231-01 is enabled when EN is pulled high. The device shuts
down when EN is pulled low.
3PFM
PFM Selection Input. Connect PFM pin to VCC/VIN for forced PWM operation. Connect
PFM pin to ground for PFM operation to improve light load efficiency.
4, 29 AGND Analog Ground.
5FB
Feedback Input. Adjust the output voltage with a resistive voltage-divider between the
regulator’s output and AGND.
6 TON On-Time Setting Input. Connect a resistor between VIN and TON to set the on time.
7 AIN Supply Input for analog functions.
8, 9, 10, 11 IN Supply Input. IN is the regulator input. All IN pins must be connected together.
12, 13, 14, 15, 16,
17, 18, 19, 26 PGND Power Ground.
20, 21, 22, 23,
24, 25 LX Switching Node.
27 BST
Bootstrap Capacitor Connection. The AOZ1231-01 includes an internal bootstrap diode.
Connect an external capacitor between BST and LX as shown in the Typical Application
diagrams.
28 VCC Output for internal linear regulator. Bypass VCC to AGND with a 1µF ceramic capacitor.
Place the capacitor close to VCC pin.
30 SS Soft-Start Time Setting Pin. Connect a capacitor between SS and AGND to set the
soft-start time.
AOZ1231-01
Rev. 1.1 June 2012
www.aosmd.com
Page 5 of 17
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: 1.5k
in series with 100pF.
2. LX to PGND Transient (t<20ns) ------ -7V to V
IN
+ 7V.
Maximum Operating Ratings
The device is not guaranteed to operate beyond the
Maximum Operating ratings.
Parameter Rating
IN, AIN, TON, PFM to AGND -0.3V to 30V
LX to AGND -2V to 30V
BST to AGND -0.3V to 36V
SS, PGOOD, FB, EN to AGND -0.3V to 6V
PGND to AGND -0.3V to +0.3V
Junction Temperature (T
J
) +150°C
Storage Temperature (T
S
) -65°C to +150°C
ESD Rating
(1)
2kV
Parameter Rating
Supply Voltage (V
IN
) 4.5V to 28V
Output Voltage Range 0.8V to 0.85*V
IN
Ambient Temperature (T
A
) -40°C to +85°C
Package Thermal Resistance
HS MOSFET 25°C/W
LS MOSFET 20°C/W
PWM Controller 50°C/W
Symbol Parameter Conditions Min. Typ. Max Units
V
IN
IN Supply Voltage 4.5 28 V
V
UVLO
Under-Voltage Lockout Threshold of V
cc
V
cc
rising
V
cc
falling 3.2
4.0
3.7
4.4 V
I
q
Quiescent Supply Current of V
cc
I
OUT
= 0, V
FB
= 1.0V, V
EN
> 2V 23mA
I
OFF
Shutdown Supply Current V
EN
= 0V 120A
V
FB
Feedback Voltage T
A
= 25°C
T
A
= 0°C to 85°C
0.792
0.788
0.800
0.800
0.808
0.812 V
Load Regulation 0.5 %
Line Regulation 1%
I
FB
FB Input Bias Current 200 nA
Enable
V
EN
EN Input Threshold Off threshold
On threshold 2.5
0.5 V
V
EN_HYS
EN Input Hysteresis 100 mV
PFM Control
Input Threshold PFM Mode threshold
Force PWM threshold 2.5
0.5 V
Input Hysteresis 100 mV
Modulator
T
ON
On Time R
TON
= 100k, V
IN
= 12V
R
TON
= 100k, V
IN
= 24V
200 250
150
300 ns
T
ON
_
MIN
Minimum On Time 100 ns
T
OFF
_
MIN
Minimum Off Time 250 ns
Electrical Characteristics
T
A
= 25°C, V
IN
= 12V, EN = 5V, unless otherwise specified. Specifications in BOLD indicate a temperature range of -40°C to +85°C.
AOZ1231-01
Rev. 1.1 June 2012
www.aosmd.com
Page 6 of 17
Soft-Start
I
SS
_
OUT
SS Source Current V
SS
= 0, C
SS
= 0.001F to 0.1F 7 10 15 A
Power Good Signal
V
PG_LOW
PGOOD Low Voltage I
OL
= 1mA 0.5 V
PGOOD Leakage Current ±1 A
V
PGH
V
PGL
PGOOD Threshold FB rising
FB falling
12
-12
15
-10
18
-8 %
PGOOD Threshold Hysteresis 3 %
T
PG_L
PGOOD Fault Delay Time (FB falling) 50 s
Under Voltage and Over Voltage Protection
V
PL
Under Voltage threshold FB falling -30 -25 -20 %
T
PL
Under Voltage Delay Time 128 s
V
PH
Over Voltage Threshold FB rising 12 15 18 %
T
UV_LX
Under Voltage Shutdown Blanking Time V
IN
= 12V, V
EN
= 0V, V
CC
= 5V 20 mS
Power Stage Output
R
DS(ON)
High-Side NFET On-Resistance V
IN
= 12V 40 60 m
High-Side NFET Leakage V
EN
= 0V, V
LX
= 0V 10 A
R
DS(ON)
Low-Side NFET On-Resistance V
LX
= 12V 25 30 m
Low-Side NFET Leakage V
EN
= 0V 10 A
Over-current and Thermal Protection
I
LIM
Valley Current Limit V
IN
= 4.5V
V
IN
= 28V
3
4A
Thermal Shutdown Threshold T
J
rising
T
J
falling
145
100 °C
Symbol Parameter Conditions Min. Typ. Max Units
Electrical Characteristics
(Continued)
T
A
= 25°C, V
IN
= 12V, EN = 5V, unless otherwise specified. Specifications in BOLD indicate a temperature range of -40°C to +85°C.
AOZ1231-01
Rev. 1.1 June 2012
www.aosmd.com
Page 7 of 17
Functional Block Diagram
TON
Generator
ISENSE
ISENSE
ILIM_VALLEY
Error Comp
Light Load
Comp
Light Load
Threshold
ILIM Comp
0.8V
ISENCE
(AC) FB
Decode
OTP
Reference
& Bias
BST
PG Logic
LX
AGNDPGND
ISENSE
ISENSE (AC)
Current
Information
Processing
Vcc
IN
AIN PGood
UVLO
LDO
TON
Timer
Q
TOFF_MIN
S
RQ
Timer
Q
TON
FB
SS
EN
VCC
PFM
AOZ1231-01
Rev. 1.1 June 2012
www.aosmd.com
Page 8 of 17
Forced CCM Mode (Io = 0A)
Vo ripple
50mV/div
Vo ripple
100mV/div
VLX
5V/div
2μs/div
Load Transient 0.8A (20%) to 3.2A (80%)
Io
1A/div
100μs/div
Full Load (4A) Start-up
Ven
5V/div
Pgood
5V/div
Vo
2V/div
lin
0.5A/div
Pgood
5V/div
VLX
5V/div
Vo
1V/div
Ilx
2.5A/div
1ms/div
Full Load Short
100μs/div
Typical Performance Characteristics
Circuit of Typical Application. TA = 25°C, VIN = 12V, VOUT = 1.05V, fs = 600kHz unless otherwise specified.
AOZ1231-01
Rev. 1.1 June 2012
www.aosmd.com
Page 9 of 17
Detailed Description
The AOZ1231-01 is a high-efficiency, easy-to-use,
synchronous buck regulators optimized for notebook
computers. The regulator is capable of supplying 4A of
continuous output current with an output voltage
adjustable down to 0.8V. The programmable operating
frequency range of 100kHz to 1MHz enables optimizing
the configuration for PCB area and efficiency.
The input voltage range for the AOZ1231-01 is 4.5V
to 28V. The constant on-time PWM with input
feed-forward control scheme results in ultra-fast transient
response while maintaining relatively constant switching
frequency over the entire input range. The true AC
current mode control scheme guarantees the regulator is
stable with ceramic output capacitors. The switching
frequency can be externally programmed up to 1MHz.
Protection features include VCC under-voltage lockout,
valley current limit, output over voltage protection, under
voltage protection, short-circuit protection, and thermal
shutdown.
The AOZ1231-01 is available in a 30-pin 5mm × 5mm
QFN package.
Input Power Architecture
The AOZ1231-01 integrates an internal linear regulator
to generate 5.3V VCC from input. If the input voltage is
lower than 5.3V, the linear regulator operates in low drop-
output mode where the VCC voltage is equal to the input
voltage minus the drop-output voltage of the internal
linear regulator.
Enable and Soft Start
The AOZ1231-01 has an external soft start feature to
limit in-rush current and ensure the output voltage
smoothly ramps up to regulation voltage. The soft start
process begins when VCC rises to 4.1V and voltage on
the EN pin is HIGH. An internal current source charges
the external soft-start capacitor and the FB voltage
follows the voltage of the soft-start pin (VSS) when it is
lower than 0.8V. When VSS is higher than 0.8V, the
FB voltage is regulated by the internal precise band-gap
voltage (0.8V). The soft-start time can be calculated by
with the following formula:
TSS(s) = 330 x CSS(nF)
If CSS is 1nF, the soft-start time will be 330µs.
If CSS is 10nF, the soft-start time will be 3.3ms.
Constant-On-Time PWM Control with Input
Feed-Forward
The control algorithm of the AOZ1231-01 is
constant-on-time PWM Control with input feed-forward.
The simplified control schematic is shown in Figure 1.
Figure 1. Simplified Control Schematic of AOZ1231-01
The high-side switch on-time is determined solely by a
one-shot with a pulse width that can be programmed by
one external resistor and is inversely proportional to the
input voltage (IN). The one-shot is triggered when the
internal 0.8V is lower than the combined information of
FB voltage and the AC current information of inductor,
which is processed and obtained through the sensed
lower-side MOSFET current once it turns-on. The
added AC current information can help the stability of
constant-on time control even with pure ceramic output
capacitors, which have a very low ESR. The AC current
information has no DC offset, which does not cause
offset with output load change, which is fundamentally
different from other V2 constant-on time control schemes.
The constant-on-time PWM control architecture is a
pseudo-fixed frequency with input voltage feed-forward.
The internal circuit of the AOZ1231-01 sets the on-time of
high-side switch inversely proportional to the IN voltage:
To achieve the flux balance of inductor, the buck
converter has the equation:
Once the product of VIN x TON is constant, the switching
frequency keeps constant and is independent with input
voltage.
0.8V
FB Voltage/
AC Current
Information
Comp
Programmable
One-Shot
IN
PWM
+
–
TON
26.3 10 12–RTON
VIN V
----------------------------------------------------------------
=(1)
FSW
VOUT
VIN TON
---------------------------
=(2)
AOZ1231-01
Rev. 1.1 June 2012
www.aosmd.com
Page 10 of 17
An external resistor between the IN and TON pin sets the
switching frequency according to the following equation:
A further simplified equation will be:
If VOUT is 1.8V, RTON is 137k, the switching frequency
will be 500kHz.
This algorithm results in a nearly constant switching
frequency despite the lack of a fixed-frequency clock
generator.
True Current Mode Control
The constant-on-time control scheme is intrinsically
unstable if the output capacitor’s ESR is not large enough
to use as an effective current-sense resistor. Ceramic
capacitors usually can not be used as an output
capacitor.
The AOZ1231-01 senses the low-side MOSFET current
and processes it into DC current and AC current
information using an Alpha & Omega proprietary
technique. The AC current information is decoded and
added on the FB pin on phase. With AC current
information, the stability of the constant-on-time control is
significantly improved even without the help of the output
capacitor’s ESR. Thus a pure ceramic capacitor solution
can be used. The pure ceramic capacitor solution can
significantly reduce the output ripple (no ESR caused
overshoot and undershoot) and uses less PCB board
area.
Valley Current-Limit Protection
The AOZ1231-01 provides valley current-limit protection
by using the RDS(ON) of the lower MOSFET current
sensing. To detect real current information, a minimum
constant off (250ns typical) is implemented after a
constant-on time. If the current exceeds the valley
current-limit threshold, the PWM controller is not allowed
to initiate a new cycle. The actual peak current is greater
than the valley current-limit threshold by an amount equal
to the inductor ripple current. Therefore, the exact
current-limit characteristic and maximum load capability
are a function of the inductor value and input and output
voltages. The current limit will keep the low-side
MOSFET on and will not allow another high-side on-time,
until the current in the low-side MOSFET reduces below
the current limit. During the current limit, the inductor
current is shown in Figure 2.
Figure 2. Inductor Current
After 128s (typical), the AOZ1231-01 considers this as a
true fail condition, turns off both high-side and low-side
MOSFETs and latches off. Only triggering the enable can
restart the AOZ1231-01.
Output Voltage Under-voltage Protection
If the output voltage is reduced 10% by over-current or
short circuit, AOZ1231-01 will wait for 128s (typical),
turns off both high-side and low-side MOSFETs and
latches off. Only triggering the enable can restart the
AOZ1231-01.
Output Voltage Over-voltage Protection
The threshold of OVP is set to 15% higher than 800mV.
When the Vfb voltage exceeds the OVP threshold, the
high-side MOSFET is turned off and the low-side
MOSFETs is turned on until Vfb voltage is less than
800mV.
Power Good Output
The power good (PGOOD) output, which is an open
drain output, requires the pull-up resistor. When the
output voltage is 10% below the nominal regulation
voltage for 50s (typical), PGOOD is pulled low. When
the output voltage is 15% higher than the nominal
regulation voltage, PGOOD is also pulled low.
When combined with the under-voltage-protection circuit,
this current-limit method is effective in almost every
circumstance. In forced-PWM mode, the AOZ1231-01
also implements a negative current limit to prevent
excessive reverse inductor currents when VOUT is
sinking current.
FSW
VOUT 1012
26.3 RTON
---------------------------------
=(3)
FSW kHz
38000 VOUT
V
RTON k
-----------------------------------------------
=(4)
Inductor
Current
Time
Ilim
Rev. 1.1 June 2012
www.aosmd.com
Page 11 of 17
AOZ1231-01
Application Information
The basic AOZ1231-01 application circuits is shown in
pages 2 and 3. Component selection is explained below.
Input Capacitor
The input capacitor must be connected to the IN pins and
PGND pins of the AOZ1231-01 to maintain steady input
voltage and filter out the pulsing input current. A small
decoupling capacitor, usually 1F, should be connected
to the VCC pin and AGND pins for stable operation of the
AOZ1231-01. The voltage rating of the input capacitor
must be greater than the 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 the input capacitor current can
be calculated by:
if let m equal the conversion ratio:
The relationship between the input capacitor RMS
current and voltage conversion ratio is calculated and
shown in Figure 3. 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 3. I
CIN
vs. Voltage Conversion Ratio
For reliable operation and best performance, the input
capacitors must have a current rating higher than
ICIN_RMS at the worst operating conditions. Ceramic
capacitors are preferred as input capacitors because of
their low ESR and high ripple current rating. Depending
on the application circuits, other low ESR tantalum
capacitors or aluminum electrolytic capacitors may 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 manufacturers is
based on a certain life time. Further de-rating may be
necessary for practical design requirements.
Inductor
The inductor is used to supply constant current to output
when it is driven by a switching voltage. For a given input
and output voltage, inductance and switching frequency
together decide the inductor ripple current, which is:
The peak inductor current is:
High inductance provides low inductor ripple current but
requires a larger size inductor to avoid saturation. Low
ripple current reduces inductor core losses. It also
reduces RMS current through the inductor and switches,
which results in less conduction loss. Usually, peak to
peak ripple current on inductor is designed to be 30%
to 50% 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.
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. They also
cost more than unshielded inductors. The choice
depends on EMI requirement, price and size.
VIN
IO
fC
IN
----------------- 1VO
VIN
---------
–
VO
VIN
---------
=
ICIN_RMS IO
VO
VIN
---------1VO
VIN
---------
–
=
VO
VIN
---------m=
0
0.1
0.2
0.3
0.4
0.5
0 0.5 1
m
ICIN_RMS(m)
IO
IL
VO
fL
-----------1VO
VIN
---------
–
=
ILpeak IO
IL
2
--------
+=
AOZ1231-01
Rev. 1.1 June 2012
www.aosmd.com
Page 12 of 17
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 is calculated by the equation below:
where,
C
O
is output capacitor value and
ESR
CO
is the Equivalent Series Resistor of the output capacitor.
When a low ESR ceramic capacitor is used as the 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 the 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
ceramic capacitors, or other low ESR tantalum are
recommended to 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.
Thermal Management and Layout
Consideration
In the AOZ1231-01 buck regulator circuit, high pulsing
current flows through two circuit loops. The first loop
starts from the input capacitors, to the IN pins, to the
LX pins, to the filter inductor, to the output capacitor and
load, and then returns to the input capacitor through
ground. Current flows in the first loop when the high side
switch is on. The second loop starts from the inductor,
to the output capacitors and load, to the low side switch.
Current flows in the second loop when the low side low
side switch is on.
In PCB layout, minimizing the board area of the two loops
reduces the noise of the circuit and improves efficiency.
A ground plane is strongly recommended to connect
input capacitor, output capacitor, and PGND pins of the
AOZ1231-01.
In the AOZ1231-01 buck regulator circuit, the major
power dissipating components are the AOZ1231-01 and
the output inductor. The total power dissipation of the
converter circuit can be measured by input power minus
output power:
The power dissipation of the inductor can be
approximately calculated by output current and DCR of
inductor:
The actual junction temperature can be calculated with
power dissipation in the AOZ1231-01 and thermal
impedance from junction to ambient:
The maximum junction temperature of the AOZ1231-01
is 150ºC, which limits the maximum load current
capability.
The thermal performance of the AOZ1231-01 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.
VOILESRCO
1
8fC
O
-------------------------
+
=
VOIL
1
8fC
O
-------------------------
=
VOILESRCO
=
ICO_RMS
IL
12
----------
=
Ptotal_loss VIN IIN VOIO
–=
Pinductor_loss IO
2
Rinductor 1.1=
Tjunction Ptotal_loss Pinductor_loss
–
JA
=
AOZ1231-01
Rev. 1.1 June 2012
www.aosmd.com
Page 13 of 17
Several layout tips are listed below for the best electric
and thermal performance.
1. The LX pins and pad are connected to internal low
side switch drain. They are low resistance thermal
conduction path and the most noisy switching node.
Connect a large copper plane to the LX pins to help
thermal dissipation.
2. The IN pins and pad are connected to the internal
high side switch drain. They are also low resistance
thermal conduction path. Connect a large copper
plane to the IN pins to help thermal dissipation.
3. Do not use thermal relief connection to the PGND
pins. Pour a maximized copper area to the PGND
pins to help thermal dissipation.
4. Input capacitors should be connected as close as
possible to the IN pins and the PGND pins to reduce
the switching spikes.
5. Decoupling capacitor CVCC should be connected as
close as possible to VCC and AGND.
6. Voltage divider R1 and R2 should be placed as close
as possible to FB and AGND.
7. Rton should be connected as close as possible to
Pin 6 (TON pin).
8. Pin 26 (PGND) is connected to the ground plane
through via. A ground plane is preferred.
9. Keep sensitive signal traces such as the feedback
trace away from the LX pins.
10. Pour copper plane on all unused board area and
connect it to stable DC nodes, like VIN, GND or
VOUT.
PGND 12
PGND 13
PGND 14
19 PGND
18 PGND
17 PGND
16 PGND
15 PGND
PGND
1
2
P
G
ND
13
P
G
ND
14
19
PG
ND
18
PG
ND
1
7
PG
ND
16
PG
ND
15
PG
ND
IN
IN
IN
IN
LX
LX
LX
AGND
SS
VCC
BST
PGND
1
2
3
4
5
6
7
P G OO D
E N
AGN D
F B
T O N
8
9
10
11
23
24
25
26
27
28
29
22
21
20
LX
LX
LX
LX
IN
AGN D
30
Rton
C in
L X
C o u t
V o
V o
Cvc c
G N D
Vc c
C b
R1
R 2
AIN
PFM
L
X
L
X
L
X
2
3
2
4
2
5
2
2
2
1
2
0
L
X
L
X
L
X
L
X
V
o
IN
I
N
I
N
I
N
7
8
9
1
0
1
1
I
N
AIN
AGND
D
4
N
D
2
9
AG
N
D
AOZ1231-01
Rev. 1.1 June 2012
www.aosmd.com
Page 14 of 17
Package Dimensions, QFN 5x5, 30 Lead EP3_S
22
23
1
30
14
15
7
8
22
23
30
14
15
7
8
TOP VIEW
SIDE VIEW
BOTTOM VIEW
L1
L2
E1 E1
E2
D3
D2
L4
L3
L5
L
L5
L5
D/2
D
B
A
E
E/2
2
INDEX AREA
(D/2xE/2)
aaa C
2x
2x
e
A3
4
A
A1
A3
SEATING
PLANE
C
30 x b
Cbbb MAB
3
1
D1
e
e/2
PIN#1 DIA
L1
L5
D3/2
C0.35x45˚
2e
A3/2
e/2
A3/2
Notes:
1. All dimensions are in millimeters.
2. The location of the terminal #1 identifier and terminal numbering convention conforms to JEDEC publication 95 SPP-002.
3. Dimension b applies to metallized terminal and is measured between 0.20 mm and 0.35 mm from the terminal tip. If the terminal
has the optional radius on the other end of the terminal, then dimension b should not be measured in that radius area.
4. Coplanarity applies to the terminals and all other bottom surface metalization.
ccc C
ddd C
aaa C
AOZ1231-01
Rev. 1.1 June 2012
www.aosmd.com
Page 15 of 17
Package Dimensions, QFN 5x5, 30 Lead EP3_S
(Continued)
Symbols Min. Typ. Max.
RECOMMENDED LAND PATTERN
Dimensions in millimeters Dimensions in inches
0.39
L3
0.0070.003—0.1660.066—
L2
0.0210.0170.0130.5360.4360.336
L1
0.006
0.004
0.197 BSC
0.000
0.031
0.001
0.035
0.002
0.039
1.00
0.05
0.90
0.02
2.22
0.80
0.00
A
A1
E
D2
D1
5.00 BSC
bbb
aaa
L
A3 0.20 REF
0.350.250.20
b0.008
0.008 REF
0.010 0.014
0.500.400.30 0.020
0.020 BSC0.50 BSC
D5.00 BSC 0.197 BSC
E1
ccc
ddd
0.004
0.003
0.15
0.10
0.10
0.08
0.0160.012
1.294 1.4941.394
e
2.12 2.32
0.97 1.07 1.17
0.30X45˚
0.4361.394
0.066
1.39
1.83
2.22
0.76
0.39
0.500 REF
0.27
0.27
UNIT: MM
0.25
0.27
0.27
E2 1.796 1.9961.896
0.490.29
0.76
L4 0.860.66
0.27
L5 0.370.17
22
23
1
30
15
7
8
14
3.66
1.896
1.07
0.55
0.25
D3
L3
L2
L1
A
A1
E
D2
D1
bbb
aaa
L
A3
b
D
E1
ccc
ddd
e
E2
L4
L5
D3
3.56 3.66 3.76 0.140 0.144 0.148
2.37 2.37
2.37 2.37
0.087
0.083 0.091
0.038 0.042 0.046
0.051 0.0590.055
0.110 0.1180.114
0.0190.0150.011
0.0340.0300.026
0.0150.0110.007
0.25
0.75
Symbols Min. Typ. Max.
AOZ1231-01
Rev. 1.1 June 2012
www.aosmd.com
Page 16 of 17
Tape and Reel Dimensions, QFN 5x5, 30 Lead EP3_S
Carrier Tape
Reel
Tape Size
12mm
Reel Size
ø330
M
ø330.0
±2.0
N
ø79.0
±1.0
UNIT: mm
G
M
W1
S
K
H
N
W
V
R
Trailer Tape
300mm min.
or 75 Empty Pockets
Components Tape
Orientation in Pocket
Leader Tape
500mm min.
or 125 Empty Pockets
H
ø13.0
±0.5
W
12.4
+2.0/-0.0
W1
17.0
+2.6/-1.2
K
10.5
±0.2
S
2.0
±0.5
G
—
R
—
V
—
Leader/Trailer and Orientation
UNIT: mm
P1
D1 P2
B0
P0 D0
E2
E1
E
A0 Feeding Direction
Package A0 B0 K0 E E1 E2D0 D1 P0 P1 P2 T
5.25
±0.10 ±0.10
5.25
±0.10
1.10 1.50 1.50 12.00
±0.10
1.75
±0.05
5.50
±0.10
8.00
±0.10
4.00
±0.05
2.00
±0.05
0.30
±0.3
+0.10/-0Min.
QFN 5x5
(12mm)
T
K0
AOZ1231-01
Rev. 1.1 June 2012
www.aosmd.com
Page 17 of 17
Part Marking
Part Number Code
Assembly Lot Code
Fab & Assembly Location
Year & Week Code
Z1231QI1
FAYWLT
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.
This datasheet contains preliminary data; supplementary data may be published at a later date.
Alpha & Omega Semiconductor reserves the right to make changes at any time without notice.
LIFE SUPPORT POLICY
ALPHA & OMEGA SEMICONDUCTOR PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL
COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS.
