YB1518
Step-up DC-DC Converter White LED Driver
Description
The YB1518 is a step-up DC-DC converter;
operates as current source to drive up to 6
white LEDs(VIN at 3.0V) or 8 LEDs(VIN at
3.4V) or 9 LEDs(VIN at 3.4V) in series.
Series connecting of the LEDs provides
identical LED currents resulting in uniform
brightness and eliminating the need for
ballast resistors. The light intensity of these
LEDs is proportional to the current passing
through them. The YB1518 switches at a
fixed frequency of ~1MHz, allowing the use
of tiny, low profile inductors and capacitors
to minimize footprint and cost in space
consideration applications for cellular
phone backlighting or other hand held
equipment.
The YB1518 can drive up to 9 white LEDs
from a single Li-Ion battery. The wide input
voltage range from 2.7V to 16V is ideal for
portable and automotive (5V/12V)
applications with higher conversion
efficiency. To control LED brightness, the
LED current can be pulsed by applying a
PWM (pulse width modulated) signal with a
frequency range of 100Hz to 1KHz to the
CTRL pin.
YB1518 has integrated Latched Over
Voltage Protection that prevents damage to
the device in case of a high impedance
output due to faulty LED or open circuit
caused by abnormal conditions.
Typical Application Circuit
Figure 1: Typical Application Circuit
Features
Built-in internal switch
2.7V to 16V input range
<1uA shutdown current
High efficiency
Internal Soft Start
Drives up to 9 white LEDs(VIN at 3.4V)
Over voltage protection 36V
Small 5-Lead SOT-23 package
100mV Low Reference Voltage
Applications
LCD Display Module
White LED Backlighting
PDAs, GPS terminals
Digital Cameras
Cellular Phone
Electronic Books
Portable Applications
YB1518 MRev.1.2 www.yobon.com.tw 1
YB1518
Step-up DC-DC Converter White LED Driver
Pin Configuration
Figure 2: YB1518 Pin Configuration
Pin Description
Tab le 1
Pin NAME Description
1
SW
2
GND Ground Pin. Connect directly to local ground plane.
3
FB
4
CTRL
5
VIN
Switching Pin. This is the collector of the internal NPN power
switch. Connect to inductor and diode. Minimize the metal
trace area connected to this pin to reduce EMI.
Feedback Pin. Reference voltage is 100mV. Connect LEDs
and a resistor at this pin. LED current is determined by the
resistance and CTRL voltage.
Shutdown Pin and Dimming Control pin.
VCTRL > 1.8V generates full-scale LED current
VCTRL < 0.4V chip is off
Switching from 0.4V to 2.0V, PWM duty cycle controls the LED
current
Input Supply Pin. Bypass this pin with a capacitor as close to
the device as possible
Ordering Information
Tab l e 2
Order Number Supplied as Package Marking
YB1518ST25 3000 units Tape & Reel Y58M
YB1518 MRev.1.2 www.yobon.com.tw 2
YB1518
(TA
Step-up DC-DC Converter White LED Driver
Absolute Maximum Ratings
VIN .........................................................................20V
SW Voltage............................................................36V
FB Voltage ............................................................... 5V
CTRL Voltage...........................................................5V
Maximum Junction Temp,TJ .............................150°C
Lead Temperature (Slokering 10 sec) ................300°C
Thermal Resistance............................................195°C
Recommended Operating Conditions
Operating Temperature ............................-40°C~85°C
Supply Voltage............................................ 2.7 V~16V
SW Voltage............................................................ 32V
Electricity Characteristics
=25°C, Vin=3.3V, Cin=1uF Cout=10uF unless otherwise noted)Table 3
Symbol Function Parameter Test Conditions Min Typ Max Units
Note:
Absolute maximum ratings are limits beyond which damage to the device may occur.
The maximum allowable power dissipation is a function of maximum function temperature , TJ(max), the
junction to ambient thermal resistance, θJA , and the ambient temperature. The maximum allowable, power
dissipation at any ambient temperature is calculated using: PD(MAX)= [TJ(max)-TA]/θJA . Exceeding the
maximum allowable power dissipation will cause excessive die temperature. All limits at temperature
extremes are guaranteed via correlation using standard statistical methods
Vin Input Voltage Range 2.7 16 V
IQ (Quiescent
Current)
VFB Feedback Voltage
ICL Switch Current Limit
IB FB Pin Bias Current VFB=100mV 1 uA
FRSW Switching Frequency 900 930 960 KHz
DTMX Maximum Duty Cycle 85 %
DTMN Minimum Duty Cycle 20 25 %
VSAT Switch Vcesat At Isw = 200mA 180 mV
ILKG
VCTL
ICTL CTRL Pin Bias Current Ctrl = 2V 40 μA
OVP
θJA Thermal Resistance 220 °C/W
Not Switching VFB = 0.3V 1.2 1.5 1.7 mA
Shutdown CTRL = 0V 0.3 1 uA
Iout=20mA,Vout=12.5V
Circuit of Figure 1
100% duty cycle 400 450 mA
Switch Leakage
Current
VCTRL for Full LED
Current
Over Voltage
Protection
90 100 110 mV
40% duty cycle 350 mA
Ctrl = 0.3V 1 μA
Full On 1.7 V
Full Off 0.3 V
34 V
YB1518 MRev.1.2 www.yobon.com.tw 3
YB1518
Step-up DC-DC Converter White LED Driver
Typical Performance Characteristics
Condition : VIN 2.8V ; 4.4V / VCRTL : 3V
VOUT ; 2pcs white LEDs
Condition : VIN 2.8V ; 4.4V / VCTRL: 3V
VOUT ; 3pcs white LEDs
Efficiency vs Vin (2WLEDs)
82
81
Efficiency(%)
80
79
78
2.7 3.0 3.3 3.6 3.9 4.2 4.5
Vin(V)
Efficiency(%)
Efficiency vs Vin (3WLEDs)
83.0
82.5
82.0
81.5
81.0
2.7 3.0 3.3 3.6 3.9 4.2 4.5
Vin(V)
YB1518 MRev.1.2 www.yobon.com.tw 4
YB1518
Step-up DC-DC Converter White LED Driver
Condition : Vin 2.8V ; 4.4V / Vctrl : 3V
VOUT ; 4pcs white LEDs
Condition : Vin 2.8V ; 4.4V / Vctrl : 3V
VOUT ; 5pcs white LEDs
Efficiency vs Vin (4WLEDs)
83
82
81
Efficiency(%)
80
79
2.7 3.0 3.3 3.6 3.9 4.2 4.5
Vin(V)
Efficiency vs Vin (5WLEDs)
83
81
79
Efficiency(%)
77
75
2.7 3.0 3.3 3.6 3.9 4.2 4.5
Vin(V)
YB1518 MRev.1.2 www.yobon.com.tw 5
YB1518
Step-up DC-DC Converter White LED Driver
Condition : Vin 2.8V ; 4.4V / Vctrl : 3V
VOUT ; 6pcs white LEDs
Condition : Vin 3.0V ;4.4V / Vctrl : 3V
VOUT ; 7pcs white LEDs
Efficiency vs Vin (6WLEDs)
82
80
78
76
Efficiency(%)
74
72
2.7 3.0 3.3 3.6 3.9 4.2 4.5
Vin(V)
Efficiency vs Vin (7WLEDs)
80
78
76
74
Efficiency(%)
72
70
2.73.03.33.63.94.24.5
Vin(V)
YB1518 MRev.1.2 www.yobon.com.tw 6
YB1518
Step-up DC-DC Converter White LED Driver
Condition : Vin 3.0V ; 4.4V / Vctrl : 3V
VOUT ; 8pcs white LEDs
Condition : Vin 3.4V ; 6.0V / Vctrl : 3V
VOUT ; 9pcs white LEDs
Efficiency vs Vin (8WLEDs)
80
78
76
74
Efficiency(%)
72
70
2.7 3.0 3.3 3.6 3.9 4.2 4.5
Vin(V)
Efficiency vs Vin (9WLEDs)
81
78
75
Efficiency(%)
72
69
3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5
Vin(V)
YB1518 MRev.1.2 www.yobon.com.tw 7
YB1518
Step-up DC-DC Converter White LED Driver
Typical Performance Characteristics
1
Supply Current (Vctrl = 0V)
0.8
0.6
uA
0.4
0.2
0
23456789
V
Switching Frequency
932.2
932
931.8
931.6
Khz
931.4
931.2
931
930.8
23456789
Vin(V)
6
5
Supply Current (Vctrl = Vin)
4
3
A
m
2
1
0
23456789
V
Vcesat
250
200
150
100
Vcesat ( mV)
50
0
50 100 150 200 250 300 350 400
Switching Current ( mA)
0.5
Switch Leakage Current
0.4
0.3
uA
0.2
0.1
0
234567 89
Vin (V)
YB1518 MRev.1.2 www.yobon.com.tw 8
CTRL Pin Bias Current
60
50
40
30
uA
20
10
0
23456789
Vin(V)
YB1518
Step-up DC-DC Converter White LED Driver
Functional Block
Operation
Figure 3: YB1518 Block Diagram
The YB1518 uses a constant frequency,
current mode control scheme to regulate
the output LED current. Its operation can
be understood by referring to the block
diagram in Figure 3. At the start of each
oscillator cycle, a voltage proportional to
the switch current is added to a ramp
output and the resulting sum is fed into the
positive terminal of the PWM comparator
(comparator-1). When this voltage exceeds
the level of the comparator negative input,
the peak current has been reached, and
the SR latch (in Control Logic) is reset and
turns off the power switch. The voltage at
the negative input of the comparator comes
from the output of the error amplifier. The
error amplifier sets the correct peak current
level to keep the output in regulation. If the
error amplifier’s output increases, more
current is delivered to the output; if it
decreases, less current is delivered.
Application Information
Soft Start and Current Limit
The internal soft start circuit minimizes the
inrush current during turning on YB1518.
The maximum switch current is limited to
about 450 mA by the chip.
LED Current and Dimming Control
The LED’s current is set by a resistor
connected at FB pin to GND using:
mV
The maximum LED current set initially can
be reduced by pulse width modulating the
CTRL. A better approach is to adjust the
feedback voltage for dimming control.
Either a DC level signal or a filtered PWM
signal can be used to control the LED
current as illustrated in Figure 4 and Figure
I
LED
=
100
R
LED
YB1518 MRev.1.2 www.yobon.com.tw 9
YB1518
Step-up DC-DC Converter White LED Driver
5 respectively. Using the above different
scheme, the LED current can be controlled
from 0% to 100% to its maximum value.
VDC(V) VFB Iout(mA)
2 0 0
1.8 2.2 0.43
1.6 9.2 1.8
1.4 19.6 3.6
1.2 31.1 6
1 43.4 8.5
0.8 63 12.3
0.6 74 14.5
0.4 86.4 16.9
0.2 96.9 19
0 102 20
Figure 4. Dimming Control Using
a DC Voltage
Duty Iout ( mA)
0% 20
20% 17.4
30% 15
40% 12.4
50% 10
60% 8
70% 6.4
80% 4.07
100% 0
PWM : 2V ; 1KHz ;
Vin=3.6V
Figure 5. Dimming Control Using
a Filtered PWM Signal
Over Voltage Protection
The YB1518 has an internal over voltage
protection circuit which also acts as an
open-circuit protection. In the cases of
open circuit or the LEDs failure, the LEDs
are disconnected from the circuit, and the
feedback voltage will be zero. The YB1518
will then switch to a high duty cycle
resulting in a high output voltage, which
may cause SW pin voltage to exceed its
maximum 34V rating. The YB1518 will
shutdown automatically until input condition
changes to bring it out of the shutdown
mode.
Inductor Selection
A 22uH inductor is recommended for most
applications to drive more than 5 LEDs.
YB1518 MRev.1.2 www.yobon.com.tw 10
YB1518
Step-up DC-DC Converter White LED Driver
Although small size and high efficiency are
major concerns, the inductor should have
low core losses at 1MHz and low DCR
(copper wire resistance).
Diode Selection
To maintain high efficiency, the average
current rating of the Schottky diode should
be large than the peak inductor current, IPK.
Schottky diode with a low forward drop and
fast switching speeds are ideal for increase
efficiency in portable application. Choose a
reverse breakdown of the Schottky diode
large than the output voltage.
Capacitor Selection
connections for the Cout capacitor can
increase the series resistance, which
directly effect output voltage ripple.
The feedback network, resister R2 should
be kept close to the FB pin to minimize
copper trace connections that can inject
noise into the system. The ground
connection for the feedback resistor
network should connect directly to an
analog ground plane. The analog ground
plane should tie directly to the GND pin. If
no analog ground plane is available, the
ground connection for the feedback
network should tie directly to the GND pin.
Trace connections made to the inductor
and Schottky diode should be minimized to
reduce power dissipation and increase
overall efficiency.
Choose low ESR capacitors for the output
to minimize output voltage ripple. Multilayer
capacitors are a good choice for this as well.
A 1uF capacitor is sufficient for 2~6 LEDs,
2.2uF is for 7~8 LEDs and 4.7uF is for 9
LEDs applications. For additional
bypassing, a 100nF ceramic capacitor can
be used to shunt high frequency ripple on
the input.
The input bypass capacitor Cin, as shown
in Figure 1, must be placed close to the IC.
This will reduce copper trace resistance
which affects input voltage ripple of the IC.
For additional input voltage filtering, a
100nF bypass capacitor can be placed in
parallel with Cin to shunt any high
frequency noise to ground. The output
capacitor, Cout, should also be placed
close to the IC. Any copper trace
YB1518 MRev.1.2 www.yobon.com.tw 11
Package Description
YB1518
Step-up DC-DC Converter White LED Driver
All the contains in this datasheet are not assuming any responsibility for use of any
circuitry described no circuit patent license are implied and Yobon reserves the right at
any time without notice to change said circuitry and specifications.
Yobon Inc. would like to receive your feedback with your recommends and suggestions
that is always welcome and with our appreciations.
YB1518 MRev.1.2 www.yobon.com.tw 12
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