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PDF AOZ1057 Data sheet ( Hoja de datos )
| Número de pieza | AOZ1057 | |
| Descripción | 3A Simple Buck Regulator | |
| Fabricantes | Alpha & Omega Semiconductors | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de AOZ1057 (archivo pdf) en la parte inferior de esta página. Total 15 Páginas | ||
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AOZ1057
EZBuck™ 3A Simple Buck Regulator
General Description
The AOZ1057 is a high efficiency, simple to use, 3A buck
regulator. The AOZ1057 works from a 4.5V to 16V input
voltage range, and provides up to 3A of continuous
output current with an output voltage adjustable down
to 0.8V.
The AOZ1057 comes in an SO-8 package and is rated
over a -40°C to +85°C ambient temperature range.
Features
● 4.5V to 16V operating input voltage range
● 40mΩ internal PFET switch for high efficiency:
up to 95%
● Externally soft start
● Output voltage adjustable to 0.8V
● 3A continuous output current
● Fixed 340kHz PWM operation
● Cycle-by-cycle current limit
● Short-circuit protection
● Output over voltage protection
● Thermal shutdown
● Small size SO-8 package
Applications
● Point of load DC/DC conversion
● PCIe graphics cards
● Set top boxes
● DVD drives and HDD
● LCD panels
● Cable modems
● Telecom/networking/datacom equipment
Typical Application
VIN
C1
22µF Ceramic
Css
82nF SS VIN
EN U1
AOZ1057 LX
COMP
RC C5
FB
L1
6.8µH
VOUT
3.3V
R1
C2, C3
22µF Ceramic
CC
AGND
PGND
D1
R2
Rev. 1.3 November 2009
Figure 1. 3.3V/3A Buck Regulator
www.aosmd.com
Page 1 of 15
Free Datasheet http://www.datasheet4u.com/
1 page  
AOZ1057
Typical Performance Characteristics
Circuit of Figure 1. TA = 25°C, VIN = VEN = 12V, VOUT = 3.3V unless otherwise specified.
Light Load (DCM) Operation
Full Load (CCM) Operation
Vin ripple
0.1V/div
Vo ripple
20mV/div
VLX
5V/div
2s/div
2s/div
Startup to Full Load
Short Circuit Protection
Vin ripple
0.1V/div
Vo ripple
20mV/div
VLX
5V/div
Vo
2V/div
Vo
2V/div
4ms/div
lin
1A/div
50% to 100% Load Transient
Vo Ripple
50mV/div
lo
1A/div
400s/div
10ms/div
Short Circuit Recovery
lin
1A/div
Vo
2V/div
10ms/div
IL
1A/div
Rev. 1.3 November 2009
www.aosmd.com
Page 5 of 15
Free Datasheet http://www.datasheet4u.com/
5 Page 
AOZ1057
where;
fC is desired crossover frequency,
VFB is 0.8V,
GEA is the error amplifier transconductance, which is 200x10-6
A/V, and
GCS is the current sense circuit transconductance, which is
6.68 A/V.
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:
CC = 2----π-----×-----R1---.-C-5----×-----f--p---1-
The previous equation above can also be simplified to:
CC = C-----O--R---×--C---R-----L-
An easy-to-use application software which helps to
design and simulate the compensation loop can be found
at www.aosmd.com.
Thermal Management and Layout
Consideration
In the AOZ1057 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 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 the Schottky diode,
to the
cathode of Schottky diode. Current flows in the second
loop when the low side diode is on.
In the 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 capaci-
tor, output capacitor, and PGND pin of the AOZ1057.
In the AOZ1057 buck regulator circuit, the major power
dissipating components are the AOZ1057, the Schottky
diode 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 in Schottky can be approximated
as:
Pdiode_loss = IO × (1 – D) × VFW_Schottky
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.
Pinductor_loss = IO × (1 – D) × VFW_Schottky
The actual AOZ1057 junction temperature can be
calculated with power dissipation in the AOZ1057 and
thermal impedance from junction to ambient.
Tjunction =
(Ptotal_loss – Pdiode_loss – Pinductor_loss) × ΘJA + Tamb
The maximum junction temperature of AOZ1057 is
150°C, which limits the maximum load current capability.
The thermal performance of the AOZ1057 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. Figure 3 on the next page
illustrates a PCB layout example as reference.
1. 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.
2. Input capacitor should be connected to the VIN pin
and the PGND pin as close as possible.
3. 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.
4. Make the current trace from LX pin to L to Co to the
PGND as short as possible.
5. Pour copper plane on all unused board area and
connect it to stable DC nodes, like VIN, GND or
VOUT.
6. The LX pin is connected to internal PFET drain. They
are low resistance thermal conduction path and most
noisy switching node. Connected a copper plane to
LX pin to help thermal dissipation. This copper plane
should not be too larger otherwise switching noise
may be coupled to other part of circuit.
7. Keep sensitive signal trace far away form the LX pin.
Rev. 1.3 November 2009
www.aosmd.com
Page 11 of 15
Free Datasheet http://www.datasheet4u.com/
11 Page | ||
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