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PDF BL8545 Data sheet ( Hoja de datos )
| Número de pieza | BL8545 | |
| Descripción | High Efficiency Low Noise PFM Step-up DC/DC Converter | |
| Fabricantes | BELLING | |
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Hay una vista previa y un enlace de descarga de BL8545 (archivo pdf) en la parte inferior de esta página. Total 6 Páginas | ||
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BL8545
REV1.0-Revised SEP 2008
High Efficiency Low Noise PFM Step-up DC/DC Converter
DESCRIPTION
The BL8545 PFM 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 500KHz to 2MHz
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 200mA 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 BL8545 be suitable for the portable devices,
which are supplied by a single battery.
FEATURES
• Up to 24V Output Voltage
• Wide Operation Range: 2V to 6V
• Maximum 2MHz Operating Frequency
• PWM Dimming Control
• Shutdown Current <1uA
• Current Limit Cycle-by-Cycle
• Low Current Sense Threshold: 200mV
• 24V Over Output Voltage Protection
• Compact SOT23-6 Package
APPLICATIONS
• Compact Back Light Module
• Power Source for LED
• Constant Current Source
BL8545 is available in SOT23-6 package that
is PB free.
TYPICAL APPLICATION
L1
VIN 10uH
D1
SS14
LED1
Cin
4.7uF
ON
OFF
VIN LX
OVP
BLCL83534050
CE FB
GND
Cout
4.7uF
LED2
LED3
LED4
R1
Figure1. BL8545 Typical Application Circuit
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1
LED17
LED18
LED19
LED20
R5
1 page  
BL8545
APPLICATION INFORMATION
Dimming Control
1. Using a PWM Signal to CE Pin
When adding the PWM signal to CE pin, the BL8545 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. The frequency range of the PWM signal is from 1 kHz to 300KHz.
2. Using a DC Voltage
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
BLLC83534050
VDC R13
90K
FB
R12
5K
LED2
LED3
R1
10
Figure 2. Dimming Control Using a DC Voltage
3. Using a Filtered PWM Signal
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
BLLC83534050
FB
R13 R12
90K
C12
0.1uF
5K
LED2
LED3
R1
10
Figure 3. Dimming Control Using a Filtered PWM Signal
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5
5 Page | ||
| Páginas | Total 6 Páginas | |
| PDF Descargar | [ Datasheet BL8545.PDF ] | |
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