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PDF AOZ1081 Data sheet ( Hoja de datos )
| Número de pieza | AOZ1081 | |
| Descripción | 1.8A High Efficiency Constant Current Regulator | |
| Fabricantes | Alpha & Omega Semiconductors | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de AOZ1081 (archivo pdf) en la parte inferior de esta página. Total 16 Páginas | ||
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AOZ1081
EZBuck™ 1.8A High Efficiency
Constant Current Regulator for LEDs
General Description
The AOZ1081 is a high efficiency, simple to use, 1.8A
buck regulator for White LED. The AOZ1081 works from
a 4.5V to 16V input voltage range, and provides up to
1.8A of continuous output current with an output voltage
adjustable down to 0.25V.
The AOZ1081 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
● 100 mΩ internal PFET switch for high efficiency:
up to 95%
● Internal Schottky Diode
● Internal soft start
● 0.25V internal reference with ±5% accuracy over
temperature
● 1.8A continuous output current
● Fixed 1MHz PWM operation
● Cycle-by-cycle current limit
● Short-circuit protection
● Under voltage lockout
● Output over voltage protection
● Thermal shutdown
● Small size SO-8 package
Applications
● Buck regulator for white LEDs
● Landscape lighting
● Flashlights
● Battery powered backlight applications
Typical Application
VIN
C1
22µF
R1
C2
VIN
EN
AOZ1081
COMP
LX
FB
AGND PGND
4.7µH
HB
LED
RFB
VOUT
C3
22µF
Rev. 1.1 April 2009
Figure 1.
www.aosmd.com
Page 1 of 16
1 page  
AOZ1081
Electrical Characteristics
TA = 25°C, VIN = VEN = 12V, VOUT = 3.3V unless otherwise specified(3)
Symbol
Parameter
Conditions
Min. Typ. Max.
VIN
VUVLO
IIN
Supply Voltage
Input Under-Voltage Lockout
Threshold
Supply Current (Quiescent)
VIN Rising
VIN Falling
IOUT = 0, VCOMP = 0.1V, VEN
>1.2V
4.5 16
4.0
3.7
23
IOFF Shutdown Supply Current
VFB Feedback Voltage
Load Regulation
VEN = 0V
1 10
0.2375 0.25 0.2625
0.5
Line Regulation
0.5
IFB Feedback Voltage Input Current
VEN EN Input Threshold
Off Threshold
On Threshold
200
0.6
2.0
VHYS
EN Input Hysteresis
MODULATOR
100
fO
DMAX
DMIN
Frequency
Maximum Duty Cycle
Minimum Duty Cycle
Error Amplifier Voltage Gain
850 1000 1150
100
12
500
Error Amplifier Transconductance
200
PROTECTION
ILIM Current Limit
VPR Output Over-Voltage Protection
Threshold
Off Threshold
On Threshold
2.5 4.0
330
240
TJ Over-Temperature Shutdown Limit
tSS Soft Start Interval
OUTPUT STAGE
150
400
High-Side Switch On-Resistance
VIN = 12V
VIN = 5V
97 130
166 200
Note:
3. Specification in BOLD indicate an ambient temperature range of -40°C to +85°C. These specifications are guaranteed by design.
Units
V
V
mA
µA
V
%
%
nA
V
mV
kHz
%
%
V/ V
µA / V
A
mV
°C
µs
mΩ
Rev. 1.1 April 2009
www.aosmd.com
Page 5 of 16
5 Page 
AOZ1081
Loop Compensation
The AOZ1081 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.
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 and can
be calculated by:
fp1
=
----------------1------------------
2π × CO × RL
The zero is a ESR zero due to output capacitor and its
ESR. It is can be calculated by:
fZ1
=
-----------------------1-------------------------
2π × CO × ESRCO
where;
CO is the output filter capacitor,
RL is load resistor value, and
ESRCO is the equivalent series resistance of output capacitor.
The compensation design is actually to shape the
converter close loop transfer function to get desired gain
and phase. Several different types of compensation
network can be used for AOZ1081. 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.
In the AOZ1081, FB pin and COMP pin are the inverting
input and the output of internal transconductance error
amplifier. A series R and C compensation network con-
nected to COMP provides one pole and one zero. The
pole is:
fp2
=
----------------G-----E----A-----------------
2π × CC × GVEA
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
CC is compensation capacitor.
The zero given by the external compensation network,
capacitor CC (C5 in Figure 1) and resistor RC (R1 in
Figure 1), is located at:
fZ2
=
-----------------1------------------
2π × CC × RC
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 frequency is also called the converter
bandwidth. Generally a higher bandwidth means faster
response to load transient. However, the bandwidth
should not be too high due to system stability concern.
When designing the compensation loop, converter
stability under all line and load condition must be
considered.
Usually, it is recommended to set the bandwidth to be
less than 1/10 of switching frequency. The AOZ1081
operates at a fixed switching frequency range from
750kHz to 1.15MHz. It is recommended to choose a
crossover frequency less than 75kHz.
fC = 75kHz
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:
RC
=
fC
×
--V----O----
VFB
×
-----2---π-----×-----C-----O------
GEA × GCS
where;
fC is desired crossover frequency,
VFB is 0.25V,
GEA is the error amplifier transconductance, which is 200x10-6
A/V, and
GCS is the current sense circuit transconductance, which is
5.64 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 byy:
CC
=
--------------1---.--5---------------
2π × RC × fp1
The equation above can also be simplified to:
CC
=
C-----O-----×-----R-----L-
RC
Rev. 1.1 April 2009
www.aosmd.com
Page 11 of 16
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet AOZ1081.PDF ] | |
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