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PDF BL8549 Data sheet ( Hoja de datos )
| Número de pieza | BL8549 | |
| Descripción | 40V Backlight LED Driver | |
| Fabricantes | BELLING | |
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BL8549
40V Backlight LED Driver with PWM Direct Dimming
DESCRIPTION
The BL8549 is a high efficiency current-mode
asynchronous, 40V boost converter for LED
backlight driving. Its input voltage ranges from
2.5V to 4.5V and it provides an adjustable
constant current output decided by the Rset
connected to BL8549’s FB pin. The LED brightness
can also be controlled by a PWM signal directly
set to CE pin, making dimming control very
simple.
The BL8549’s switching frequency is set to
600KHz, and it will automatically switch between
PFM and PWM mode based on the load current,
thus to enhance the converter efficiency at light
load as well as heavy load.
BL8549 consists of many protection blocks such
as UVLO, output voltage over voltage protection,
and thermal protection to keep the chip and load
safe under unexpected environment.
The BL8549 is available in the tiny DFN2x2-6 and
SOT23-6 package.
FEATURES
Adjustable Output Voltage, Vfb=0.2V
Output voltage 40V, driving up to 12 LED string
Range of operation input voltage: 2.5 – 4.5V
Output Overvoltage Protection @40V
CE pin PWM direct dimming function
Line regulation: 0.1%/V (typ.)
Load regulation: 10mV (typ.)
High efficiency, up to 90% in driving 10 LEDs
Environment Temperature: -20C~85C
APPLICATIONS
Smartphone
7” MID
Portable DVD
TFT LCD bias
Portable LED lighting or torch
Other application need high voltage
TYPICAL APPLICATION and PIN OUT
BL8549
Efficiency for Driving 10 LEDs
Efficiency VS Iout for 10 LEDs
100
95
90
85
80
75
70
65
60 Vin=3.6V
55
50 Vin=3.8V
45 Vin=4.2V
40
0
10 20 30 40 50
Output Current (mA)
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1 page  
Switching waveform Vin=4.2V, 10 LEDs
(CH1=Vin, CH2=Vout, CH3=SW, CH4=Isw)
BL8549
Startup waveform Vin=3.6V, 10 LEDs
(CH1=Vin, CH2=Vout, CH3=SW, CH4=Isw)
FUNCTIONAL DECRIPTIONS
Loop Operation
The BL8549 is a high voltage, high-efficiency, DC-to-DC step-up LED driver, capable of driving up to 10 LEDs. It integrates
with a 300m MOSFET, with external schottky diode. It uses a PWM current-mode control scheme. An error amplifier
integrates error between the FB signal and the internal reference voltage. The output of the integrator is then compared
to the sum of a current-sense signal and the slope compensation ramp. This operation generates a PWM signal that
modulates the duty cycle of the power MOSFETs to achieve regulation for output voltage.
Current Limit
There is a cycle-by-cycle current limit on the high-side MOSFET of 1A(typ). When the current flowing out of SW exceeds
this limit, the low-side MOSFET turns off and the external schottky diode rectifier turns on. Unlike the traditional method
of current limiting by limiting the voltage at the external compensation node, which usually has large variation due to
duty cycle variance, this type of peak current limiting scheme provides a relatively more accurate limit for output current,
thereby lowering the requirements for system design.
Light Load Operation
Traditionally, a fixed current mode constant frequency PWM DC-DC regulator always switches even when the output
load is small. When energy is shuffling back and forth through the power MOSFETs, power is lost due to the finite
RDSONs of the MOSFETs and parasitic capacitances. At light load, this loss is prominent and efficiency is therefore very
low. BL8549 employs a proprietary control scheme that improves efficiency in this situation by enabling the device into a
power save mode during light load, thereby extending the range of high efficiency operation.
PWM BRIGHTNESS DIMMING CONTROL at CE PIN
When CE pin is forced a PWM signal with frequency higher than 5KHz, the chip is in dimming mode. The internal circuit
changes the feedback voltage according to the duty cycle of the PWM signal. The feedback voltage (Vfb) is simply
defined as below:
Vfb=200mV x Duty Cycle (%)
To shut down the chip, one has to make the CE signal low, and keep its low state for more than 2.5ms.
www.belling.com.cn
5
5 Page | ||
| Páginas | Total 6 Páginas | |
| PDF Descargar | [ Datasheet BL8549.PDF ] | |
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