BL8548

BL8548
Max. 3MHz, Variable Frequency Step-up DC/DC Converter
DESCRIPTION
FEATURES
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.
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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
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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.
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
Figure1. BL8548 Typical Application Circuit
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1
BL8548
ORDERING INFORMATION
BL8548 □1
□2 □3
Code
1
2
3
MARKING INFORMATION
Product Classification
Description
Temperature & Rohs:
BL8548CB6TR
Marking
C: -40~85°C, Pb Free Rohs Std.
Package Type:
6
4
LE: Product Code
LEZZ
LEZZ
B6: SOT-23-6
Packing Type:
ZZ: Date Code
TR: Tape & Reel (Standard)
PIN DESCRIPTION
Pin No.
Symbol
1
LX
2
GND
3
FB
Pin for Feedback Voltage
4
CE
Chip Enable Pin (Active with “H”), connect to VIN if not used.
5
OVP
Over Voltage Protection
6
VIN
Power Supply
Description
Switching node
Ground
BLOCK DIAGRAM
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5
2
1
2
3
BL8548
ABSOLUTE MAXIMUM RATING
Parameter
Value
Max Input Voltage
CE Pin Voltage
LX Pin Output Current
LX Pin Voltage
Operating Junction Temperature (TJ)
Ambient Temperature (TA)
Power Dissipation
SOT-23-6
Storage Temperature (Ts)
Lead Temperature & Time
-0.3V to 8V
-0.3V to (Vin+0.3V)
1.8A
19.4V
125C
-40C to 85C
400mW
-40C to 150C
260C, 10Sec
ELECTRICAL CHARACTERISTICS
(Ta=25ºC，VIN=3V，VCE=3V, unless otherwise noted)
Symbol
Item
Conditions
VIN
Operating Input Voltage
VFB
IFB
Feedback Voltage
FB Pin Bias Current
IQ
Quiescent Current
ILIMIT
VCESAT
ILX
VCEH
VCEL
ICE
VOVP
Typ.
Max.
Unit
6
V
0.210
100
120
1.0
V
nA
uA
uA
2
0.190
10
0.200
45
93
0.4
VFB=0.3V
VCE=0V
Maximum switching
Frequency
Switching Current Limit
Switching Saturation
Voltage
Switching pin Leak Current
CE Voltage High
CE Voltage Low
CE Pin Bias Current
Over Voltage Protection
FMAX
Min.
VFB=0V, Floating OVP Pin
3
MHz
1.8
A
ILX=300mA
260
mV
VLX=5V
VCE=0 to 3V
VCE=3 to 0V
VIN=VCE=3V
0.11
uA
V
V
uA
V
1.5
0.4
18
19
TYPICAL PERFORMANCE CHARACTERISTICS
CE Pin Current vs. Temperature
(VIN=VCE))
80
70
60
50
40
30
20
10
0
50
CE Pin Current(uA)
CE Pin Bias Curren(uA)
CE Pin Bias Current vs. EN pin Voltage
(VIN=VCE)
40
30
20
10
0
-50
0
1
2
3
4
5
0
25
50
75
100
Temperature
CE Pin Voltage(V)
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-25
6
VCE=2.5V
3
VCE=3V
VCE=6V
BL8548
Quiescent Current vs. Supply Voltage
(VCE=0V)
Quiescent Current vs. Supply Voltage
(VCE=VIN,VFB=0.3V)
120
100
80
60
40
20
0
Quiescent Current(uA)
Quiescent Current(uA)
1.0
0.8
0.6
0.4
0.2
0.0
0
1
2
3
4
5
0
6
1
2
Supply Voltage(V)
FB Pin Voltage(V)
FB Pin Voltage(V)
0.22
0.20
0.18
0.16
0.14
0.22
0.20
0.18
0.16
3
4
5
6
-50
-25
0
Supply Voltage(V)
Maximum Output Currenr(mA)
40
60
80
100
120
VIN=3V
VIN=6V
4
3
2
1
0
4
5
6
Supply Voltage(V)
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100
500
400
300
200
100
0
8
12
16
Output Voltage(V)
Vin=2.5V
Switch Frequency vs. Supply Voltage
(4LEDs*100mA)
3
75
600
4
Output Current(mA)
VIN=2.5V
50
Maximum Output Currenr vs. Output Voltage
100
80
60
40
20
0
20
25
Temperature(ºC)
Efficiency vs. Output Current
(4LEDs)
Efficiency(%)
6
0.12
2
Switch Frequency(MHz)
5
0.14
0.12
2
4
FB Pin Voltage vs. Temperature
FB Pin Voltage vs.Supply Voltage
0
3
Supply Voltage(V)
4
Vin=3V
20
Vin=6V
24
BL8548
APPLICATION INFORMATION
Dimming Control
1. Using a PWM Signal to CE Pin
4. PCB Layout
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.
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
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
LED2
LC3320
BL8548
LED3
FB
VDC
R13
R12
90K
R1
10
5K
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
Figure 4. Recommended Component Placement
LED2
LC3320
BL8548
LED3
FB
PWM R14
R13
90K
C12
0.1uF
R12
5K
R1
10
Figure 3. Dimming Control Using a Filtered PWM Signal
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BL8548
PACKAGE INFORMATION
Package
SOT-23-6
Devices per reel
Package dimension：
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6
3000Pcs
Unit
mm