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PDF AOZ1950 Data sheet ( Hoja de datos )
| Número de pieza | AOZ1950 | |
| Descripción | Boost Regulator White LED Driver | |
| Fabricantes | Alpha & Omega Semiconductors | |
| Logotipo |  |
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AOZ1950
Boost Regulator White LED Driver
General Description
The AOZ1950 is a high-efficiency boost regulator with
internal 60V MOSFET and input protection switch. The
part is designed to drive up to twelve white LEDs in
series. The AOZ1950 supports two dimming control
methods: analog dimming and PWM dimming. In analog
dimming mode, the LED current can be linearly adjusted
for ±12% with a DC voltage on DIM pin. In PWM dimming
mode, the LEDs can be turned on and off by toggling EN
pin with a square wave, and the brightness is
proportional to the duty cycle of the control signal.
AOZ1950 is a fixed OFF pulse regulator with adaptive
pulse width as a function of input and output voltage.
Typical switching frequency is 800kHz. This allows the
use of low-profile inductor and capacitors.
The AOZ1950 works from a 2.7V to 5.5V input voltage
range supporting a wide range of applications. Other
features include cycle-by-cycle current limit, Input voltage
short circuit protection switch, open-LED over-voltage
protection, input under-voltage lockout, thermal
shutdown and soft-start.
The AOZ1950 is available in a tiny 3mm x 3mm
10-pin DFN package and is rated over a -40°C to +85°C
operating temperature range.
Features
z 2.7V to 5.5V input voltage range
z 60V/350mΩ internal N-channel MOSFET
z Drives up to 12 White LEDs
z 800kHz typical switching frequency with adaptive
pulse width control
z 150ns nominal OFF pulse
z 300mV feedback regulation
z Analog dimming via DIM pin
z PWM dimming via EN pin
z Cycle-by-cycle current limit
z Short circuit protection switch
z Open LED over-voltage protection
z Thermal shutdown protection
z Internal soft-start
z Small 3mm x 3mm DFN package
Applications
z Portable DVD Players
z GPS Systems
z Smart Phones
z Sub Notebook PC
Typical Application
L1
22μH
VIN
2.7V-5.5V
R1
1.5kΩ
C3
22nF
C1
4.7μF
IND
VIN
LX
VOUT
AOZ1950
DIM PGND
AGND
EN
COMP
C4
1nF
FB
C2
0.47μF
R2
15Ω
Rev. 1.0 January 2010
www.aosmd.com
Page 1 of 14
1 page  
AOZ1950
Functional Description
AOZ1950 is a constant off time boost converter that is
ideal for white LED backlight applications. The operating
input voltage range is from 2.7V to 5.5V and can support
up to 12 in series LED’s, with the maximum allowed
output voltage set at 53V. The LED current is set by a
series feedback resistor, located at the bottom of the LED
string. The feedback voltage of the controller is set at
300mV for minimum power loss. AOZ1950 features two
dimming control modes, analog and digital dimming. In
analog dimming, fine adjustment of ±12% of the LED
current can be achieved. In PWM digital dimming, a logic
level pulse width is used to set the output LED current.
The duty cycle of the PWM is proportionally to the LED
current. In this dimming mode, the PWM frequency is set
between from 200Hz to 1kHz with duty cycle from 10% to
100%.
Adaptive Constant Pulse Width Control
In a typical constant off time controller, the switching
frequency changes with duty cycle.The duty cycle
relationship of the boost converter entails that if either the
input voltage decreases or the output voltage increases,
the (1-D) off time will decrease. AOZ1950 features an
adaptive constant off-time control that senses the input
and output voltage while maintaining a constant
switching frequency of 800 kHz. In a typical LED
application of 5.5V input and 40V output (12 LEDs), the
off pulse width will be approximately 150ns.
300
250
VIN = 20V
200
150
100
VIN = 36V
VIN = 50V
50
0
2.5 3.0 3.5 4.0 4.5 5.0
Input Voltage (V)
Figure 2. Pulse Width vs. Input Voltage
5.5
300
250
200
150
100
50
VOUT = 5.5V
VOUT = 3.3V
VOUT = 2.7V
0
20 25 30 35 40 45
Output Voltage (V)
Figure 3. Pulse Width vs. Output Voltage
50
Over Current Protection
Under normal operation, cycle by cycle over-current
protection will limit the input peak inductor current from
increasing beyond 1.1A nominally.
Output Short Protection
When an output to ground short is detected, a secondary
short circuit protection current level of 1.3A is activated.
During this event the PMOS input protection switch along
with the output boost switch are disabled simultaneously
and the AOZ1950 will shutdown. The system will restart
with a power cycle when either VIN or EN are toggled.
Over Voltage Protection
An over-voltage protection scheme monitors the output
voltage and limits the maximum transient to 53V. The
voltage rating is defined for the maximum voltage stress
of the Mosfet, output boost diode, and output capacitors.
Rev. 1.0 January 2010
www.aosmd.com
Page 5 of 14
5 Page 
AOZ1950
Based on the duty cycle arrangement, the controller will
signal the internal driver to turn-off the NMOS to initiate
the fixed off time. After the NMOS is fully off, the
continuous inductor current continues to freewheel
through the output boost diode. The key parasitics in this
loop consist of PBC trace inductance from the anode to
the LX connection and lastly the connection from cathode
to power ground return. Both input and output capacitors
should be ceramic in type to achieve low ESR and ESL
specifications.
C1
Alpha and Omega
LED Boost Driver
AOZ1950
LED Boost Driver
VIN L1
D1
AOZ1950DI
RSET
RCOMP GND
LX
CCOMP
CC
DIM
EN
COUT
vOUT
LED
STRING
PGND 1
IND 2
VIN 3
VOUT 4
FB 5
PAD1
(LX)
PAD2
(AGND)
10 LX
9 EN
8 AGND
7 DIM
6 COMP
3x3 DFN-10
(Top View)
Figure 14. Example of AOZ1950 PCB Layout and DFN-10 Pin-out
Below are some key tips in minimize the two main
switching loops and improving noise immunity
1. Maximized the copper area to the GND pin and the
VIN pin for improved thermal dissipation.
2. Incorporate a ground plane on both top and bottom
layers if possible.
3. To minimize trace inductance connects the device to
the LX pin with a short wire and adoption of this
technique for connections to the output capacitor and
ground.
4. Add thermal vias for the GND pad for improved
thermal dissipation between top and bottom layers.
5. To maximize thermal dissipation pour incorporate
copper planes in unused areas.
6. Route sensitive signals such as FB and COMP
pins a far distance away from the LX switching node
and pin.
In the AOZ1950 boost regulator circuit, the three major
power dissipating components are the AOZ1950 and
output inductor. The total power dissipation of converter
circuit can be measured by difference between the input
and output power.
Ptotal_loss = (VIN × IIN) – (VO × IO) (Eq. 14)
The power dissipation of inductor can be approximately
calculated by input current and DCR of inductor.
Pinductor_loss
=
I2
IN
×
Rinductor
×
1.1
(Eq. 15)
The actual AOZ1950 junction temperature can be
calculated with power dissipation and the thermal
impedance from junction to ambient.
Tjunction = (Ptotal_loss – Pinductor_loss) × Θ + Tamb
(Eq. 15)
The maximum junction temperature of AOZ1950 is rated
at 145ºC The thermal performance of the AOZ1950 is
strongly affected by the PCB layout and proper care
should be taken to ensure that the device will operate
under the recommended environmental conditions.
Rev. 1.0 January 2010
www.aosmd.com
Page 11 of 14
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet AOZ1950.PDF ] | |
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