BELLING BL8545

BL8545
Max. 3MHz, Variable Frequency Step-up DC/DC Converter
DESCRIPTION
FEATURES
The BL8545 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 24V 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
24V Over Output Voltage Protection
Compact SOT23-6 Package
APPLICATIONS
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Compact Back Light Module
Power Source for LED
Constant Current Source
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.
BL8545 is available in SOT23-6 package that
is PB free.
TYPICAL APPLICATION
D1
L1
10uH
VIN
SS14
LED1
LED17
LED2
Cin
Cout
4.7uF
4.7uF
VIN
ON
OFF
LED3
LX
OVP
LED19
LED4
LED20
LC3300
BL8545
CE
FB
GND
R1
Figure1. BL8545 Typical Application Circuit
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LED18
1
R5
BL8545
ORDERING INFORMATION
BL8545 □
1 □
2 □
3
Code
MARKING INFORMATION
Product Classification
Description
Temperature & Rohs:
1
2
3
Marking
C: -40~85°C, Pb Free Rohs Std.
Package Type:
LEZZ
B6: SOT-23-6
Packing Type:
BL8545CB6TR
6
LE: Product
Code
ZZ: Date Code
5
LEZZ
1
TR: Tape & Reel (Standard)
PIN DESCRIPTION
Pin No.
Symbol
Description
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
Switching node
Ground
BLOCK DIAGRAM
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2
4
2
3
BL8545
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)
1.6A
24V
125C
-40C to 85C
250mW
-40C to 150C
260C, 10Sec
ELECTRICAL CHARACTERISTICS
(Ta=25ºC，VIN=3V，VCE=3V, unless otherwise noted)
Symbol
Item
Conditions
Min.
VIN
Operating Input Voltage
2
VFB
IFB
Feedback Voltage
FB Pin Bias Current
0.190
10
IQ
Quiescent Current
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
ILIMIT
VCESAT
ILX
VCEH
VCEL
ICE
VOVP
Typ.
Max.
Unit
6
V
0.210
100
120
1.0
V
nA
uA
uA
VFB=0.3V
VCE=0V
0.200
45
93
0.4
VFB=0V, Floating OVP Pin
3
MHz
1.6
A
ILX=300mA
260
mV
VLX=5V
0.11
uA
VCE=0 to 3V
VCE=3 to 0V
VIN=VCE=3V
1.5
V
V
uA
V
0.4
18
24
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
Temperature
6
CE Pin Voltage(V)
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-25
VCE=2.5V
3
VCE=3V
VCE=6V
100
BL8545
Quiescent Current vs. Supply Voltage
(VCE=VIN,VFB=0.3V)
Quiescent Current(uA)
Quiescent Current(uA)
Quiescent Current vs. Supply Voltage
(VCE=0V)
1.0
0.8
0.6
0.4
0.2
0.0
0
1
2
3
4
5
120
100
80
60
40
20
0
0
6
1
2
0.220
0.200
0.180
0.160
0.140
0.120
3
4
5
6
75
100
0.200
0.180
0.160
0.140
0.120
6
-50
-25
0
25
50
Temperature(ºC)
Efficiency vs. Output Current
(4LEDs)
Maximum Output Currenr vs. Output Voltage
600
500
100
80
Maximum Output
Currenr(mA)
Efficiency(%)
5
0.220
Supply Voltage(V)
60
40
20
0
0
20
40
60
80
100
VIN=2.5V
VIN=3V
3
2
1
0
4
5
6
Supply Voltage(V)
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200
100
8
12
16
Output Voltage(V)
Vin=2.5V
VIN=6V
4
3
300
4
Switch Frequency vs. Supply Voltage
(4LEDs*100mA)
2
400
0
120
Output Current(mA)
Switch Frequency(MHz)
4
FB Pin Voltage vs. Temperature
FB Pin Voltage(V)
FB Pin Voltage(V)
FB Pin Voltage vs.Supply Voltage
2
3
Supply Current(V)
Supply Voltage(V)
4
Vin=3V
20
Vin=6V
24
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.
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
BL8545
LC3300
LED3
FB
VDC
R13
R12
90K
R1
5K
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
LED2
LC3300
BL8545
LED3
FB
PWM R14
R13
R12
90K
5K
C12
0.1uF
R1
10
Figure 3. Dimming Control Using a Filtered PWM Signal
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5
BL8545
PACKAGE INFORMATION
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6