Datasheet

UNISONIC TECHNOLOGIES CO., LTD
L5101
LINEAR INTEGRATED CIRCUIT
WHITE LED STEP-UP
CONVERTER
„
DESCRIPTION
The UTC L5101 is a constant current step-up PWM DC/DC
converter optimized to drive white LEDs. It can drive LEDs in series
with a Li-Ion cell.
The switching frequency of the internal NPN is up to 1.2MHz.
High frequency allows the use of tiny external components and the
current setting resistor has minimum power dissipation for the low
feedback voltage of 95mV. The built-in OVP prevents the UTC
L5101 damage from the open load condition.
Series connection of LEDs provides identical LED currents which
contributes to uniform brightness, saving the use of ballast
resistors.
The UTC L5101 is universally used in cellular phones, PDAs ,
DSCs, handheld devices, and white LED display backlighting.
„
6
5
4
1
2
3
SOT-26
FEATURES
* Open Circuit and Over Voltage Protection
* High Efficiency: 86% Typical
* Switching Frequency: 1.2MHz
* Supply Current is 1.0mA
* Matches LED Current
* Requires Tiny Inductor and Capacitors
* Halogen Free
„
ORDERING INFORMATION
Ordering Number
L5101G-AG6-R
„
Package
SOT-26
Packing
Tape Reel
MARKING
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Copyright © 2009 Unisonic Technologies Co., Ltd
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LINEAR INTEGRATED CIRCUIT
„
PIN CONFIGURATION
„
PIN DESCRIPTION
PIN NO.
1
2
3
4
5
6
PIN NAME
Shutdown
Ground
SYMBOL
DESCRIPTION
SHDN Tie to higher than 1.5V to enable device, 0.3V or less to disable device.
GND
Reference voltage is 95mV. Connect cathode of lowest LED and
Feedback
FB
resistor here. Calculation formula: RFB=95mV/ILED
Connect inductor/diode here. Minimize trace area at this pin to reduce
Switch
SW
EMI.
Power input
VIN
Bypass VIN to GND with a capacitor sitting as close to VIN as possible.
Over voltage protection
OVP The internal NPN will turn off when VOUT >27V.
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L5101
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LINEAR INTEGRATED CIRCUIT
BLOCK DIAGRAM
VIN
5
95mV
Over Voltage
Comparator
1.25V
VREF
+
27V
-
PWM
Comparator
-
Control
Logic
Driver
6
OVP
4
SW
2
GND
Q1
+
+
M
FB 3
Error
AMP
RC
RAMP
GENERATOR
CC
SHDN 1
+
Current AMP.
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1.2MHz
Oscillator
-
RS
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LINEAR INTEGRATED CIRCUIT
ABSOLUTE MAXIMUM RATING
PARAMETER
SYMBOL
RATINGS
UNIT
Input Voltage
VIN
6
V
SW Voltage
VSW
33
V
FB Voltage
VFB
6
V
SHDN Voltage
VSHDN
6
V
OVP Voltage
VOVP
34
V
Junction Temperature
TJ
+125
℃
Operating Temperature Range
TOPR
-20 ~ +85
℃
Storage Temperature Range
TSTG
-40 ~ +150
℃
Note: Absolute maximum ratings are those values beyond which the device could be permanently damaged.
Absolute maximum ratings are stress ratings only and functional device operation is not implied.
„
ELECTRICAL CHARACTERISTICS (VSHDN=3V, VIN=3V, Ta=25℃, unless otherwise specified.)
PARAMETER
Operating Voltage
Supply Current
ERROR AMPLIFIER
Feedback Voltage
FB Input Bias Current
OSCILLATOR
Switching Frequency
Maximum Duty Cycle
POWER SWITCH
SW ON Resistance
Switch Leakage Current
CONTROL INPUT
High
Low
OVER VOLTAGE PROTECTION
OVP Input Resistance
OVP Threshold
Shutdown Voltage
SYMBOL
VIN
IIN
VFB
IFB
TEST CONDITIONS
Switching
Non switching
VSHDN=0V
fSW
DC
RIN(OVP)
VTHR(OVP) 1V Hysteresis typical
UNIT
V
mA
μA
95
100
105
mV
nA
0.8
85
1.2
90
1.6
MHz
%
1.4
0.1
5
1
Ω
μA
0.3
V
V
1.8
32
MΩ
V
ILEAK (SW)) VSW=33V
ON
OFF
MAX
5.5
5
2
1.0
85
RON(SW)
VIH(SHDN)
VIL(SHDN)
TYP
2
1
0.1
VFB=95mV
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MIN
2.5
1.5
0.6
22
1.2
27
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LINEAR INTEGRATED CIRCUIT
TEST CIRCUIT
Fig.1 Test Circuit
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LINEAR INTEGRATED CIRCUIT
APPLICATION INFORMATION
Recommended Component Selection
* Inductor Selection: A 10μH inductor is recommended for most applications.
* Capacitor Selection: The small size of ceramic capacitor makes it ideal for UTC L5101 applications, X5R and X7R
types are recommended because of their stable characteristics, 1μF input capacitor with 1μF
output capacitor is sufficient for most UTC L5101 applications.
* Diode Selection: Schottky diode, for its low forward voltage drop and fast reverse recovery, is an ideal choice for
the UTC L5101 diode. A Schottky diode rated 100mA to 200mA is sufficient for most UTC L5101
applications, and the higher current rating usually have larger diode capacitance which can
cause significant switching losses at the 1.2MHz switching frequency.
LED Current Control
A feedback resistor (precision 1% recommended) as feedback resistor control the LED current. (RFB in Figure 1)
* Feedback reference voltage: 95mV.
* LED current is 95mV/RFB.
* The formula for RFB selection: RFB=95mV/ILED
Open-Circuit Protection
The OVP(Over Voltage Protection) protects the voltage lower than its maximum level under the open circuit
condition, which is caused by the failure or disconnection of the LEDs. The above undesired fault conditions will
cause the feedback voltage falling to 0V, then the UTC L5101 increases duty circle resulting in a high voltage in SW
pin.
Dimming Control
There are three different ways of dimming control circuits as follows:
1. Using a PWM signal
L1
10µH
D1
VIN
VIN
SW
OVP
C2
1µF
UTC L5101
C1
1µF
SHDN
GND
PWM
FB
R2
R1
51K
1K
RFB
4.7Ω
Fig. 2 Dimming Control Using a PWM Signal
Fig. 3 Dimming Control with a PWM Signal
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LINEAR INTEGRATED CIRCUIT
APPLICATION INFORMATION(Cont.)
2. Using a DC Voltage
L1
10µH
D1
VIN
VIN
OVP
SW
C2
1µF
UTC L5101
C1
1µF
SHDN
FB
GND
VDC
0~5V
R2
R1
51K
1K
RFB
4.7Ω
Fig. 4 Dimming Control Using a DC Voltage
3. Using a Filtered PWM Signal
L1
10µH
D1
VIN
VIN
C1
1µF
SW
OVP
UTC L5101
SHDN
GND
PWM
FB
R3
5.1K
C2
1µF
R1
1K
R2
51K
C3
0.1µF
RFB
4.7Ω
Fig. 5 Dimming Control Using a Filter PWM Signal
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LINEAR INTEGRATED CIRCUIT
TYPICAL APPLICATION CIRCUIT
Fig. 6 Six White LEDs Application in Li-Ion Battery
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TYPICAL CHARACTERISTICS
Switching Frequency (MHz)
Feedback Voltage (mV)
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LINEAR INTEGRATED CIRCUIT
Supply Current vs. Supply Voltage
Supply Current vs. Supply Voltage
1.95
1.35
Supply Current (mA)
1.34
1.90
1.33
1.32
FB=VIN
Non-Switching
1.31
1.85
FB=GND
Switching
1.30
1.80
1.29
2.5
3.0
3.5
4.0 4.5
5.0
2.5
5.5 6.0
3.5
4.0 4.5
5.0
5.5 6.0
Supply Voltage (V)
Supply Voltage (V)
3LEDs Efficiency vs. LED Current
RDS(ON) vs. Supply Voltage
1.4
3.0
90
VIN=3.6V
85
VIN=3.0V
80
Efficiency (%)
RDS(ON) (Ω)
1.3
1.2
1.1
75
3LEDs,
L1=10μH
70
65
VIN=4.2V
60
55
1.0
2.5
3.0 3.5
4.0 4.5
5.0
5.5
6.0
Supply Voltage (V)
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0
5
10
15
20
LED Current (mA)
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TYPICAL CHARACTERISTICS
4LEDs Efficiency vs. LED Current
90
VIN=3.6V
85
VIN=3.0V
80
Efficiency (%)
„
LINEAR INTEGRATED CIRCUIT
4LEDs,
L1=10μH
75
70
65
VIN=4.2V
60
0
5
10
15
20
LED Current (mA)
UTC assumes no responsibility for equipment failures that result from using products at values that
exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or
other parameters) listed in products specifications of any and all UTC products described or contained
herein. UTC products are not designed for use in life support appliances, devices or systems where
malfunction of these products can be reasonably expected to result in personal injury. Reproduction in
whole or in part is prohibited without the prior written consent of the copyright owner. The information
presented in this document does not form part of any quotation or contract, is believed to be accurate
and reliable and may be changed without notice.
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