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DC Converter & WLED Driver
y
EFFICIENCY (%)
D
1
Schottk
FIGN
S
E
4.7u/2V
6.8
u
=4.5~5.5V
L
1
…
4.7u/1V
O
R
1
YB1521
High Power Step-Up DC-
Description
The YB1521 is a step-up DC-DC converter
which operating as current source to drive
up 45 white LEDs (3S15P) in parallel /
series configuration from a 5V system rail.
Series connecting of 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 YB1521 is a fixed
frequency of 1.3MHz, 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 wide input voltage range from 2.5V to
5.5V is idea for portable applications with
higher conversion efficiency. To control
LED brightness, the LED current can be
pulsed by applying a PWM signal with a
frequency which is typically 50 KHz to the
EN pin.
Features
2.5V to 5.5V Input Voltage Range
Built In Power MOSFET
Drive Up to 15V @400mA at 5V Vin
Less than 1µA Shutdown Current
Up to 94% efficiency
Over Voltage Protection@18V
UVLO, Thermal Shutdown
Internal 1.6A Current Limit
200mv Low Reference Voltage
Built In Soft Start
PWM Dimming
SOT23-5 Package
Green Package (RoHS) Available
Applications
Cellular and Smart Phones
Handheld Computers and PDAs
Small LCD Displays
GPS Terminals
MP3 Players
Digital Still and Video Cameras
Electronic Books
Typical Application Circuit
VI
YB1521
Figure 1: Typical Application Circuit Figure 2: Efficienc
15 strings
100
90
80
70
60
50
4 4.5 5 5.5 6
Efficiency vs. Input Voltage
I
=100mA L=10μH
OUT
I
=180mA
OUT
INPUT VOLTAGE (V)
YB1521 MRev.1.1 www.yobon.com.tw 1
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DC Converter & WLED Driver
High Power Step-Up DC-
Pin Configuration
Figure 3: Pin Configuration
Pin Assignment & Description
YB1521
Table1
Pin NAME Description
1 SW
2 GND Ground pin. Connect directly to local ground plane.
3 FB
4 EN
5 IN
Switching Pin. This is the drain of internal power MOSFET
switch. Connect the power inductor and output rectifier to SW.
Feedback Pin. Reference voltage is 200mV. Connect LEDs and
a resistor at this pin. LED current is determined by the
resistance and FB voltage.
Shutdown Pin and Dimming Control Pin. 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
Table2
Order Number Package Type
Supplied As Package Marking
YB1521ST25 SOT23-5 3000 Units Tape & Reel
YB1521 MRev.1.1 www.yobon.com.tw 2
Y521
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DC Converter & WLED Driver
YB1521
High Power Step-Up DC-
Absolute Maximum Ratings (Note 1)
VIN to GND ............................ -0.3V to 6V
VEN to GND ........................... -0.3V to 6V
VSW to GND......................... -0.3V to 18V
Junction Temperature ................... 150℃
Storage Temperature .......-55℃ to 150℃
Lead Temperature......................... 300℃
ESD HBM ........................................ 3KV
ESD MM .........................................250V
Recommended Operating Conditions
Supply Voltage VIN............... 2.5V to 5.5V
Operating Temperature .......-40℃ to 85℃
Output Voltage ......................... 0V to 15V
Thermal Information (Note 3)
θJA............................................ 220℃ / W
Note:
1. Exceeding these ratings may damage the device.
2. The device is not guaranteed to function outside of its operating conditions.
3. θJA is measured in free air at TA = 25℃ on a low effective thermal conductivity board.
(Note 2)
YB1521 MRev.1.1 www.yobon.com.tw 3
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DC Converter & WLED Driver
YB1521
High Power Step-Up DC-
Electrical Characteristics
Table4 (VIN=5V, VEN=5V, TA=25°C, unless otherwise noted.)
Parameters Symbol Test Conditions MIN TYP MAX Units
Input Voltage Range VIN 2.5 5 5.5 V
Quiescent Current IQ VFB=0.3V 0.2 0.8 mA
Shutdown Current ISD VEN=0V, I
I
= 260mA, V
Feedback Voltage VFB
FB Input Bias Current V
Switch On-Resistance R
Maximum Duty Cycle DTMX V
Switching Frequency
EN Threshold
EN Threshold V
EN Dimming Frequency
Switch Current Limit I
Under Voltage Lock Out UVLO VIN Rising 2.25 2.45
UVLO Hysteresis 100 mV
Over Voltage Protection OVP 16 18 22 V
Thermal Shutdown TSD
DSON
FSW
V
ENH
VEN Rising, VIN = 2.5V 0.8 V
ENL
1 1.6 A
ILM
OUT
10.5V
= 0.2V 0.1 µA
FB
0.4
= 0V 85 92 %
FB
VEN Rising, VIN = 5V 1 1.5 2 V
20 50 KHz
The Hysteresis = 20℃
= 0mA 0.1 1 µA
OUT
=
OUT
180 200 220 mV
1 1.3 1.6 MHz
160
Ω
V
℃
YB1521 MRev.1.1 www.yobon.com.tw 4
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DC Converter & WLED Driver
High Power Step-Up DC-
Typical Performance Characteristics
Steady State Operation
VIN =5V, 39 LEDS, 260mA
YB1521
Startup Waveforms
VIN =5V, 39 LEDS, 260mA
Startup Waveforms into an Open Load
VIN =5V, 39 LEDS, 260mA
YB1521 MRev.1.1 www.yobon.com.tw 5
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DC Converter & WLED Driver
High Power Step-Up DC-
Functional Block
YB1521
Figure 4: Function Block
Operation
The YB1521 features 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.
When this voltage exceeds the level of the
comparator negative input, the peak
current has been reached, and the SR
latch 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 output of error
amplifier increases, more current is
delivered to the output; if it decreases, less
current is delivered.
Application Information
Inrush Current
The YB1521 has internal soft-start to limit
the amount of current through the IN pin at
startup and to also limit the amount of
overshoot on the output. The current limit is
increased by 4 steps to give a total
soft-start time of 160µs.
LED Current and Dimming Control
The LED’s current is set by a resistor
connected at FB pin to GND:
I
= 200mV / R1.
LED
The maximum LED current set initially can
YB1521 MRev.1.1 www.yobon.com.tw 6
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DC Converter & WLED Driver
20K
0.1uF
YB1521
High Power Step-Up DC-
be reduced by pulse width modulating the
EN. A better approach is to adjust the
internal reference voltage for dimming
control by a logic signal illustrated in Figure
5. YB1521 contains circuitry to support this
automatically. The typical dimming frequency is
50KHz and recommended not to lower
than 20KHz. Besides the EN dimming
control scheme, either a DC level signal or
a filtered PWM signal can be used to
control the LED current as illustrated in
Figure 6 and Figure 7 respectively. The
average current through the LEDs will
increase linearly to the duty cycle of the
c o n t r o l l i n g P W M s i g n a l .
YB1521
EN
FB
Figure 5: PWM Dimming Control Using a Logic
Signal
YB1521
VDC
80K
R1
FB
R2
20K
Figure 6: Dimming Control Using a DC Voltage
R2
80K
YB1521
FB
R3
20K
R1
Figure 7: Dimming Control Using a Filtered
PWM Signal
Over Voltage Protection
The YB1521 has an internal over voltage
protection circuit which also acts as an
open-circuit protection. In the case of open
circuit or the LEDs failure, the LEDs are
disconnected from the circuit, and the
feedback voltage will be zero. The YB1521
will then switch to a high duty cycle
resulting in a high output voltage, which
may cause SW voltage to exceed its
maximum 18V rating. The YB1521 will
shutdown automatically until the power is
recycled.
Inductor Selection
A 6.8µH is recommended to drive 39 LEDs
in series/parallel. Although small size and
high efficiency are major concerns, the
inductor should have low core losses at
1.3MHz and low DCR (copper wire
resistance). A higher 10µH inductor is
recommended to improve efficiency.
Diode Selection
To maintain high efficiency, the average
current rating of the Schottky diode should
be larger than the peak inductor current.
Schottky diode with a low forward drop and
fast switching speeds are idea for
increasing efficiency in portable application.
Choose a reverse breakdown of the
YB1521 MRev.1.1 www.yobon.com.tw 7
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DC Converter & WLED Driver
YB1521
High Power Step-Up DC-
Schottky diode large than the output
voltage.
Capacitor Selection
Choose low ESR capacitors for the output
to minimize output voltage ripple. The
ceramic capacitor is a good choice for this
as well. A 4.7µF output capacitor is
sufficient for most applications. For
applications desire a smaller output
capacitance, a 2.2µF may be used. A 4.7µF
ceramic capacitor is recommended for the
input capacitance in the real system.
PCB Layout Consideration
Proper layout of the high frequency
switching path is critical to prevent from
noise and electromagnetic interference
problems. Due to high frequency switching,
the length and area of all the traces
connected to the switch node should be
minimized.
YB1521 MRev.1.1 www.yobon.com.tw 8
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DC Converter & WLED Driver
YB1521
High Power Step-Up DC-
Package Information (SOT23-5)
The information described herein is subject to change without notice.
Yobon does not assume any responsibility for use of any circuitry or applications described herein, nor
does it convey any patent license.
YB1521 MRev.1.1 www.yobon.com.tw 9
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