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PDF BL8548 Data sheet ( Hoja de datos )
| Número de pieza | BL8548 | |
| Descripción | Variable Frequency Step-up DC/DC Converter | |
| Fabricantes | BELLING | |
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BL8548
Max. 3MHz, Variable Frequency Step-up DC/DC Converter
DESCRIPTION
The BL8548 variable frequency step-up Converter
drives white LEDs with a constant current to
provide backlight in cell phones, PDAs, and other
hand-held devices. It features allowing series
connection of the white LEDs so that the LED
currents are identical for uniform brightness. An
enable input can be pulsed repeatedly to adjust
LEDs brightness. The fast 3MHz operation
frequency allows for smaller capacitor and
inductor. Fault condition protection uses cycle-by
cycle current limiting to sense maximum inductor
current and over-voltage protection. The 0.2V
low reference voltage minimized the power loss
across the current sense resistor.
The converter can operate from 2V to 6V, and
capable of delivering maximum 250mA output
current at 4-LEDs application with 3V input
voltage. Quiescent current drawn from power
source is as low as 120uA. All of these features
make BL8548 be suitable for the portable devices,
which are supplied by a single battery.
FEATURES
Up to 19V Output Voltage
Wide Operation Range: 2V to 6V
Maximum 3MHz Operating Frequency
PWM Dimming Control
Shutdown Current <1uA
Current Limit Cycle-by-Cycle
Low Current Sense Threshold: 200mV
19V Over Output Voltage Protection
Compact SOT23-6 Package
APPLICATIONS
Compact Back Light Module
Power Source for LED
Constant Current Source
BL8548 is available in SOT23-6 package that is PB
free.
TYPICAL APPLICATION
BL8548
www.belling.com.cn
Figure1. BL8548 Typical Application Circuit
1
1 page  
APPLICATION INFORMATION
Dimming Control
1. Using a PWM Signal to CE Pin
When adding the PWM signal to CE pin, the
BL8548 is turned on or off by the PWM signal, so
the LEDs operate at either zero or full current.
The average LED current increase proportionally
with the duty cycle of the PWM signal.
2. Using a DC Voltage to FB Pin
From the Figure 2, we can add a DC voltage to FB
pin, we adjust the LED current by Changing the
DC voltage, which control the brightness, DC
voltage range is from 0V to 2V.
LED1
BLLC83534280
FB
VDC R13
R12
90K 5K
LED2
LED3
R1
10
Figure 2. Dimming Control Using a DC Voltage
3. Using a Filtered PWM Signal to FB Pin
The filtered PWM signal can be considered as an
adjustable DC voltage. It can be used to replace
the variable DC voltage source in dimming control.
The circuit is shown in Figure 3.
LED1
PWM R14
BLLC83534280
FB
R13 R12
90K
C12
0.1uF
5K
LED2
LED3
R1
10
Figure 3. Dimming Control Using a Filtered PWM Signal
BL8548
4. PCB Layout
Layout is critical to achieve clean and stable
operation. The switching power stage requires
particular attention. Follow these guidelines for
good PC board layout:
1) Place decoupling capacitors as close to the IC as
possible
2) Connect input and output capacitors to the
same power ground node with a star ground
configuration then to IC ground.
3) Keep the high-current paths as short and wide
as possible.
4) If possible, connect VIN, LX, and GND separately
to a large copper area to help cool the IC to
further improve efficiency and long-term
reliability.
5) Ensure all feedback connections are short and
direct. Place the feedback resistors as close to
the IC as possible.
6) Route high-speed switching nodes away from
sensitive analog areas
Figure 4. Recommended Component Placement
www.belling.com.cn
5
5 Page | ||
| Páginas | Total 6 Páginas | |
| PDF Descargar | [ Datasheet BL8548.PDF ] | |
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