AOSMD AOZ1615

AOZ1615
1.5A/3MHz Buck Regulator
General Description
Features
The AOZ1615 is a high-performance, easy-to-use
buck regulator. Its 3MHz switching frequency, low
quiescent current and small solution size make it an
ideal choice for portable applications.
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The AOZ1615 has a patented light load mode
architecture allowing up to 85% efficiency at 1mA
load currents, enabling longer standby times in
battery operated systems.
The AOZ1615 has and input voltage range of 2.5V to
5.5V and provides up to 1.5A of output current with
an output voltage adjustable down to 0.6V.
The AOZ1615 is available in a tiny 2mm X 3mm
8-pin DFN package and is rated over a -40°C to
+85°C ambient temperature range.
2.5V to 5.5V input voltage range
0.1µA shutdown current
Automatic PFM/PWM mode switching
Output voltage adjustable down to 0.6V
Fixed output voltages available
±2% initial accuracy
Up to 1.5A continuous output current
3MHz Constant frequency operation
Low drop-out operation – 100% duty cycle
Cycle-by-cycle current-limit
Thermal overload protection
Excellent load transient response
Internal soft-start
Tiny 2mm X 3mm DFN-8 package
Applications
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Smart phones
Personal media players
MP3 players
Digital still cameras
Wireless modems and LANs
Portable USB devices
Typical Application
L1
VIN
2.5V to 5.5V
LX
IN
AOZ1615DI
C1
10µF
PGND
VOUT
1.5A
1.0µH
R1
FB
C2
R2
OFF ON
EN
AGND
Analog Ground
Power Ground
Rev. 1.0 November 2011
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Page 1 of 14
AOZ1615
Ordering Information
Part Number
Temperature Range
Package
Environmental
AOZ1615DI
-40°C to +85°C
8-Pin 2mm x 3mm DFN
Green Product
AOS Green Products use reduced levels of Halogens, and are also RoHS compliant.
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Pin Configuration
PGND
1
VIN
2
8
LX
7
NC
AGND
NC
3
6
EN
AGND
4
5
FB
8-Pin 2mm x 3mm DFN
(Top View)
Pin Description
Part Number
Pin Name
1
2
3, 7
4
PGND
IN
NC
AGND
5
FB
6
8
PAD
EN
LX
AGND
Rev. 1.0 November 2011
Pin Function
Power Ground.
Input Supply.
No Connect.
Analog Ground.
Feedback Input. Connect an external resistive voltage divider to FB to set the output
voltage.
Enable Input. The device is enabled when EN is High and disabled with EN is Low.
Switching Node.
Analog Ground.
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Page 2 of 14
AOZ1615
Absolute Maximum Ratings
Recommended Operating Ratings
Exceeding the Absolute Maximum Ratings may damage the
device.
This device is not guaranteed to operate beyond the
Recommended Operating Ratings.
Parameter
Rating
Parameter
IN, EN, FB to AGND
LX to AGND
PGND to AGND
Storage Temperature (TS)
Junction Temperature (TJ)
Max. Soldering Temperature (10s)
(1)
ESD Rating
-0.3V to +6V
-0.3V to VIN +0.3V
-0.3V to +0.3V
-65°C to +150°C
+150°C
+300°C
2kV
Supply Voltage (VIN)
Ambient Temperature (TA)
Junction Temperature (TJ)
Package Thermal Resistance
2x3 DFN-8 (θJA)
Rating
2.5V to 5.5V
-40°C to +85°C
Internally Limited
55°C/W
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 = 3.6V, EN = IN unless otherwise specified. Specifications in BOLD indicate a temperature range of
-40°C to +85°C.
Symbol
VIN
VUV
Parameter
IIN
Input Voltage Range
Under-Voltage Lockout
Under-Voltage Lockout
Hysteresis
Input Supply Current
VFB
Feedback Reference Voltage
IFB
Feedback Bias Current
Enable Input High Voltage
Enable Input Low Voltage
Enable Bias Current
IEN
Conditions
Min.
2.5
2.11
Typ.
Max
Units
2.3
5.5
2.49
V
V
100
EN = IN, VFB = 1V, no load
EN = AGND
TA = 25°C, no load
TA = -40°C to +85°C, no load
0.588
0.585
mV
40
0.01
0.600
0.600
0.01
65
0.1
0.612
0.615
0.1
0.01
0.8
0.1
1.5
VEN = 5.5V
µA
V
µA
V
V
µA
Oscillator
fSW
T(ON)MIN
Switching Frequency
Operating Duty Cycle
Minimum On-Time
2.25
Positive Current Limit
Thermal Shutdown Threshold
Thermal Shutdown Hysteresis
1.7
3
3.75
100
MHz
%
ns
3
A
°C
°C
70
Protection
ILIM+
2.2
+145
40
Output Stage
RDS(ON)P
RDS(ON)N
PFET On Resistance
NFET On Resistance
LX Leakage Current
Rev. 1.0 November 2011
ILX = 50mA sourcing
ILX = 50mA sinking
VEN = 0V, VLX = 0V or VIN, VIN = 5V
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150
120
-1
1
mΩ
mΩ
µA
Page 3 of 14
AOZ1615
Output Voltage Selection for AOZ1615
The output voltage of the AOZ1615 can be
programmed through the resistor network connected
from VOUT to FB to AGND. The resistor from FB to
AGND should be 100kΩ to keep the current drawn
through this network below the 6μA quiescent current
level in PFM mode. The output voltage of the
adjustable AOZ1615 parts ranges from 0.6V to 3.3V.
The output voltage formula is:
Table 1. Output Voltage Resistor Selection Table
for Various VOUT Voltages
VOUT
R1
R2
L
CIN
COUT
C5
(V)
(kΩ)
(kΩ)
(μH)
(μF)
(μF)
(pF)
1.1
83
100
1
10
22
10
1.2
100
100
1
10
22
10
 R1

VOUT = VFB 
+ 1
R
2


1.3
117
100
1
10
10
10
1.5
150
100
1
10
10
10
where;
1.6
167
100
1
10
10
10
VOUT = Output Voltage (V)
1.7
183
100
1
10
10
10
1.8
200
100
1
10
10
10
1.875
213
100
1
10
10
10
2.5
317
100
1
10
10
10
2.8
367
100
1
10
10
10
3.3
450
100
1
10
10
10
VFB = Feedback Voltage (0.6V typical)
R1 = Feedback Resistor from VOUT to FB (Ω)
R2 = Feedback Resistor from FB to AGND (Ω)
A 10pF bypass capacitor C5 on the evaluation board,
in parallel with the feedback resistor from VOUT to FB
is chosen for increased stability throughout the
voltage range.
Rev. 1.0 November 2011
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Page 4 of 14
AOZ1615
Functional Block
IN
3MHz
Oscillator
EN
Output
Logic
Control
UVLO
Thermal
Shutdown
ISENSE
Amp
LX
PGND
ILIMIT
Comp
IMIN
Threshold
PFM
PWM
FB
Error
Amp
Master
Logic
VREF
600mV
AGND
Rev. 1.0 November 2011
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Page 5 of 14
AOZ1615
Typical Performance Characteristics
Rev. 1.0 November 2011
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Page 6 of 14
AOZ1615
Typical Performance Characteristics (continued)
Rev. 1.0 November 2011
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Page 7 of 14
AOZ1615
Application Information
The AOZ1615 has a patented light load mode
architecture which allows up to 85% efficiency at 1mA
load currents, enabling longer standby times in battery
operated systems.
The AOZ1615 is a high efficiency step down DC-DC
buck converter that operates typically at 3MHz fixed
Pulse Width Modulation (PWM) at medium to heavy
load currents. The AOZ1615 can deliver a constant
voltage from a single Li-Ion battery with an input
voltage range from 2.5V to 5.5V. By using voltage
mode architecture with synchronous rectification, the
AOZ1615 has the ability to deliver up 1.5A of
continuous current depending on the input voltage,
output voltage, ambient temperature and inductor
chosen.
There are two modes of operations depending on the
current consumption, PFM (Pulse Frequency
Modulation) and PWM (Pulse Width Modulation). For
ultra-low current, the device operates in the PFM
mode to obtain high efficiency that is characteristic of
the PFM mode. The device operates in the PWM
mode when the output current exceeds the load
current of approximately 100mA or higher.
Additional features include under voltage lockout, over
current protection, thermal shutdown and soft-start.
Inductor Selection
There are two main considerations when choosing an
inductor; the inductor should not saturate and the
inductor current ripple should be small enough to
achieve the desire output voltage ripple. A 1μH
inductor with a saturation current of at least 2A is
recommended for the AOZ1615 full load application.
For maximum efficiency, the inductor’s resistance
(DCR) should be as low as possible. For given input
and output voltage, inductance and switching
frequency together decide the inductor ripple current,
which is:
∆IL =
VOUT  VOUT
× 1 −
f × L 
VIN




The peak inductor current is:
IPEAK = IOUT +
∆IL
2
High inductance gives 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 inductor and switches,
which results in less conduction loss. Usually, peakto-peak ripple current on inductor is designed to be
20% to 30% of output current.
When selecting the inductor, make sure that 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 losses on an inductor need to
be checked for thermal and efficiency requirements.
Surface mount inductors in different shapes 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.
Input Capacitor
The input capacitor must be connected to the VIN and
PGND pins of AOZ1615 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. For
greater
capacitor
performance,
the
working
capacitance voltage should be twice VIN.
The input ripple voltage can be approximated by using
the equation below:
∆VIN =
 V
I OUT
× 1 − OUT
f × CIN 
VIN
 VOUT
×
 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:
ICIN _ RMS = IOUT ×
V OUT
VIN
 VOUT
1 −

VIN





if we let m equal the conversion ratio:
VOUT
=m
VIN
The relationship between the input capacitor RMS
current and voltage conversion ratio is calculated and
shown below in Figure 1. It can be seen that when
VOUT is half of VIN, CIN is under the worst current
stress. The worst current stress on CIN is 0.5 x IOUT.
Rev. 1.0 November 2011
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Page 8 of 14
AOZ1615
0.5
switching frequency dominates. Output ripple is
mainly caused by capacitor value and inductor ripple
current. The output ripple voltage calculation can be
simplified to:
0.4
ICIN_RMS(m)
IOUT
0.3
∆VO = ∆IL ×
0.2
0.1
0
0
0.5
m
1
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:
∆VO = ∆IL × ESRCO
Figure 1. 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 current rating. 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.
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:

1
∆VO = ∆IL ×  ESRCO +
8
f
×
× CO

1
8 × f × CO




where,
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.
In a buck converter, output capacitor current is
continuous. The RMS current of the output capacitor
is decided by the peak-to-peak inductor ripple current.
It can be calculated by:
I CO _ RMS =
∆IL
12
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 the inductor ripple current is high, the output
capacitor could be overstressed.
Thermal Shutdown
In most applications the AOZ1615 does not dissipate
much heat due to its high efficiency. But in an
application where the AOZ1615 is running at high
ambient temperature with low supply voltage and high
duty cycle, the heat dissipated may exceed the
maximum junction temperature. If the junction
temperature reaches approximately 140°C (typical),
the internal High Side and Low Side MOSFET
switching is disabled until the temperature on the die
has fallen sufficiently below 105°C. The device
remains in thermal shutdown until the junction
temperature falls below the thermal shutdown
hysteresis.
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
Rev. 1.0 November 2011
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Page 9 of 14
AOZ1615
Undervoltage Lockout
The undervoltage lockout circuit prevents the device
from malfunctioning at low input voltages and from
excessive discharge of the battery by disabling the
output stage of the converter. The AOZ1615 will
resume normal operation when the input supply
voltage rises high enough to properly function. The
undervoltage lockout threshold is typically 2.3V.
Soft Start
The AOZ1615 has a soft-start circuit that limits the
inrush current during startup. Soft start is activated
when EN goes from logic low to logic high after VIN
reaches 2.3V.
Over Current Protection (OCP)
The sensed inductor current signal is also used for
over current protection. Since the AOZ1615 employs
peak current mode control, the COMP voltage is
proportional to the peak inductor current. The COMP
voltage is limited to be between 0.4V and 2.5V
internally. The peak inductor current is automatically
limited cycle-by-cycle.
When the output is shorted to ground under fault
conditions, the VFB is lower than 0.425V, the high
side switch will turn off, then AOZ1615 will initiate a
soft start.
Enable
The EN pin of the AOZ1615 is active high. Connect
the EN pin to VIN if the enable function is not used,
pulling it to ground will disable the AOZ1615. Do not
leave it open. The voltage on EN must be above 2V to
enable the AOZ1615. When voltage falls below 0.6V,
the AOZ1615 is disabled. If an application circuit
requires the AOZ1615 to be disabled, an open drain
or open collector circuit should be used to interface
with the EN pin.
Low Drop Out Operation
The AOZ1615 can operate at 100% duty cycle. In this
state, the high side p-channel MOSFET is always on.
This allows the output to follow the input voltage as it
drops below the regulation voltage.
Rev. 1.0 November 2011
Thermal management and layout consideration
In the AOZ1615 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 pin, 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
inductor, to the output capacitors and load, to the low
side N-MOSFET. Current flows in the second loop
when the low side N-MOSFET is on.
In PCB layout, minimizing the two loops area reduces
the noise of the circuit and improves efficiency. A
ground plane is strongly recommended to connect the
input and output capacitors, as well as the PGND pin
of the AOZ1615.
In the AOZ1615 buck regulator circuit, the major
power dissipating components are the AOZ1615 and
the output inductor. The total power dissipation of
converter circuit can be measured by input power
minus output power.
Ptotal _ loss = VIN × IIN − VO × IO
The power dissipation of the inductor can be
approximately calculated by output current and DCR
of inductor.
2
Pinductor _ loss = IO × Rinductor × 1.1
The actual junction temperature can be calculated
with power dissipation in the AOZ1615 and thermal
impedance from junction to ambient.
(
)
T junction = Ptotal _ loss − Pinductor _ loss × ΘJA
The maximum junction temperature of AOZ1615 is
140ºC, which limits the maximum load current
capability. Please see the thermal de-rating curves for
maximum load current of the AOZ1615 under different
ambient temperature.
The thermal performance of the AOZ1615 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.
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Page 10 of 14
AOZ1615
The AOZ1615 is an exposed pad DFN-8 package.
Several layout tips are listed below for the best
electric and thermal performance.
1. The exposed pad is connected to PGND. Connect
a large copper plane to this pad to help thermal
dissipation.
2. Do not use thermal relief connection from the VIN
pin and the PGND pin. Pour a maximized copper
area to the PGND pin and the VIN pin to help
thermal dissipation.
3. Input capacitor should be connected as close as
possible to the VIN pin and the PGND pin. For
optimal performance of the device, place bulk
capacitor and de-coupling capacitor no further
than 50mils from the device.
Rev. 1.0 November 2011
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.
5. Make the current trace from LX pin to L to CO to
PGND as short as possible.
6. Pour copper planes on all unused board area and
connect them to stable DC nodes, like VIN, GND
or VOUT.
7. Keep sensitive signal traces away from the LX
pin.
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Page 11 of 14
AOZ1615
Package Dimensions, DFN 2x3, 8 Lead EP1_S
RECOMMENDED LAND PATTERN
Dimensions in millimeters
Symbols
Min.
A
A1
b
c
D
D1
D2
D3
E
E1
E2
E3
e
0.70
-0.20
0.195
1.55
0.15
0.35
0.60
1.65
Nom.
Max.
0.75
0.80
-0.05
0.25
0.30
0.203 0.211
2.00 BSC
1.60
1.65
0.20
0.25
0.125 BSC
3.00 BSC
0.40
0.45
0.65
0.70
1.70
1.75
0.50 BSC
Dimensions in inches
Min.
0.028
-0.008
0.0076
0.061
0.006
0.014
0.024
0.065
Nom.
Max.
0.030
0.031
-0.002
0.010
0.012
0.008 0.0083
0.079 BSC
0.063
0.065
0.008
0.010
0.005 BSC
0.118 BSC
0.016
0.018
0.026
0.028
0.067
0.069
0.002 BSC
UNIT: mm
NOTE
1.
CONTROLLING DIMENSION IS MILLIMETER. CONVERTED INCH DIMENSIONS ARE NOT NECESSARILY EXACT.
Rev. 1.0 November 2011
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Page 12 of 14
AOZ1615
Tape and Reel Dimensions, DFN 2x3, 8 Lead EP1_S
Carrier Tape
P2
P1
A- A
A
E1
D0
D0
K0
E2
A0
P0
T
E
A
B0
Feeding Direction
UNIT: mm
Package
DFN 2X3
(8mm)
A0
3.35
±0.10
B0
3.20
±0.10
K0
D0
D1
E
E1
E2
P0
P1
P2
T
1.10
±0.10
1.50
+0.10
-0.00
1.00
+0.25
-0.00
8.00
+0.30
-0.10
1.75
±0.10
3.50
±0.05
4.00
±0.10
4.00
±0.10
2.00
±0.05
0.23
±0.020
Reel
W1
S
R
K
M
H
N
UNIT: mm
Tape Size
Reel Size
M
N
W1
H
S
K
R
8mm
∅180
∅180.0
±0.50
60.0
±0.50
8.4
+1.5
-0
13.0
±0.20
1.5
min.
13.5
min.
3.0
±0.50
Leader/Trailer and Orientation
Trailer Tape
300mm min.
Rev. 1.0 November 2011
Components Tape
Orientation in Pocket
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Leader Tape
500mm min.
Page 13 of 14
AOZ1615
This datasheet contains preliminary data; supplementary data may be published at a later date.
Alpha and 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.
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. 1.0 November 2011
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.
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Page 14 of 14