BL8549

BL8549
40V Backlight LED Driver with PWM Direct Dimming
DESCRIPTION
FEATURES
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.
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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: -20C~85C
APPLICATIONS
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.
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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.
Smartphone
7” MID
Portable DVD
TFT LCD bias
Portable LED lighting or torch
Other application need high voltage
The BL8549 is available in the tiny DFN2x2-6 and
SOT23-6 package.
TYPICAL APPLICATION and PIN OUT
Efficiency for Driving 10 LEDs
Efficiency VS Iout for 10 LEDs
100
95
90
BL8549
85
Efficiency (%)
80
75
70
65
60
Vin=3.6V
55
Vin=3.8V
50
Vin=4.2V
45
40
0
10
20
30
Output Current (mA)
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1
40
50
BL8549
PACKAGE, MARK and ORDERING INFORMATION
Package
DFN2x2-6
Mark
Explanation
Ordering
Information
Package
SOT23-6
LT:
Product ID:
Product Code BL8549CKCTR
LT
YW
YW:
Date Code
SW
CE
VIN
6
5
4
LTYW
XXYW
Devices/Reel:
3000
1
2
COMP GND
3
FB
Mark
Explanation
Ordering
Information
LT:
Product Code
Product ID:
BL8549CB6TR
YW:
Date Code
Devices/Reel:
3000
SOT23-6
PINOUT DESCRIPTION
NAME
FB
Comp
GND
SW
PIN #
DFN2x2-6 SOT23-6
1
3
2
1
3
2
4
6
CE
5
5
VIN
6
4
DESCRIPTION
Feedback input with reference voltage set to 0.2V
Compensation pin, to connect a 220nF capacitor to make loop stable.
Ground.
Power switching node to connect inductor
Chip enable, but a PWM signal with various duty cycle can directly sent to CE pin to
achieve the backlight dimming
Power input, 1uf input capacitor is recommended.
BLOCK DIAGRAM
FB
SW
Vin
Comp
CE
GND
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BL8549
ABSOLUTE MAXIMUM RATING
Parameter
Value
Max Input Voltage
Max Output Voltage (SW pin)
Max Operating Junction Temperature(Tj)
Ambient Temperature(Ta)
DFN2x2-6 (JC)
Package Thermal Resistance
DFN2x2-6 (JA)
Storage Temperature(Ts)
Lead Temperature & Time
ESD (HBM)
5.5V
40V
125C
-20C – 85C
20C / W
140C / W
-40C - 150C
260C, 10S
>2000V
Note: Exceed these limits to damage to the device. Exposure to absolute maximum rating conditions may affect
device reliability.
RECOMMENDED WORK CONDITIONS
Parameter
Value
Input Voltage Range
Operating Junction Temperature(Tj)
2.5V – 4.5V
-20C –125C
ELECTRICAL CHARACTERISTICS
(VIN=12V, TA=25C)
Symbol
Parameter
Conditions
Vin
Input Voltage Range
Vref
Feedback Voltage
Vin=3.6V, Vce=Vin
VUVLO
UVLO Voltage
Vin H-->L, Iout=0.5A
Ifb
Iq
LnReg
Shutdown, Vin=3.6V
Vin=2.5V to 4.5V
Vin=Vce=3.6V
Low side Switch Rdson
Isw=200mA
Ilimit
Peak Inductor Current Limit
Vin=3.6V, Vout=32V
Vceh
CE High Threshold
Vcel
CE Low Threshold
Vovp
Output Over-Voltage Protection
Vce=3.6V
TSD
Over Temperature Proection
Hystersis=40C
Toff
CE pin pulse width to shutdown
CE high to low
Fpwm_CE
4.5
V
0.210
V
V
0.1
0.4
uA
0.6
1.0
mA
1
5
uA
%/V
600
750
KHz
300
500
mohm
0.8
1
1.4
A
1
1.5
3
V
0.3
V
40
42
V
150
C
ms
KHz
2.5
10
3
Unit
0.1
450
CE PWM dimming frequency
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0.200
Max
2.5
Active, Vfb=1V, No Switching
Switching Frequency
RdsonH
0.190
Feedback Leakage current
Quiescent Current
Typ
2.5
Line Regulation
Fsoc
Min
50
BL8549
TYPICAL PERFORMANCE CHARACTERISTICS
(Vin=3.6V, L=22uH, Cin=1uF, Cout=1uF, TA=25C, unless otherwise stated)
Efficiency VS Output Current
100
95
95
90
90
85
85
80
80
Efficiency (%)
Efficiency (%)
Efficiency VS Iout for 10 LEDs
100
75
70
65
60
75
70
Vin=3.6V
55
6Pcs LED
8Pcs LED
50
Vin=4.2V
45
4Pcs LED
60
55
Vin=3.8V
50
65
10Pcs LED
45
40
40
0
10
20
30
40
50
0
10
Output Current (mA)
30
40
50
Output Current (mA)
FB Voltage Vs. PWM Duty Cycle
Frequency Vs. Vin for 10 LEDs
240
600
220
590
200
580
180
570
FB Voltage (mV)
Switching Frequency (KHz)
20
560
550
540
530
160
140
120
100
80
60
520
40
510
20
0
500
2.5
3.0
3.5
4.0
4.5
0%
5.0
Vin (V)
20%
40%
60%
80%
100%
PWM Duty (%)
Switching waveform Vin=2.5V, 10 LEDs
Switching waveform Vin=3.6V, 10 LEDs
(CH1=Vin, CH2=Vout, CH3=SW, CH4=Isw)
(CH1=Vin, CH2=Vout, CH3=SW, CH4=Isw)
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BL8549
Switching waveform Vin=4.2V, 10 LEDs
Startup waveform Vin=3.6V, 10 LEDs
(CH1=Vin, CH2=Vout, CH3=SW, CH4=Isw)
(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.
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BL8549
PACKAGE OUTLINE
Package
DFN2x2-6
Devices per reel
3000
Unit
mm
Devices per reel
3000
Unit
mm
Package specification：
Package
SOT23-6
Package specification：
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