YOBON YB1521

YB1521
High Power Step-Up DC-DC Converter & WLED Driver
Description
Features
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.
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
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.
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
Efficiency vs. Input Voltage
100
L1
= 4.5~5.5V
D1
Schottk
6.8u
4.7u/2 V
4.7u/1 V
I
L=10μH
90
S
15 strings
YB1521
…
E
EFFICIENCY (%)
VI
IOUT =100mA
IOUT =180mA
80
70
60
O
50
GN
F
4
R1
Figure 1: Typical Application Circuit
YB1521 MRev.1.1
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4.5
5
5.5
6
INPUT VOLTAGE (V)
Figure 2: Efficiency
1
YB1521
High Power Step-Up DC-DC Converter & WLED Driver
Pin Configuration
Figure 3: Pin Configuration
Pin Assignment & Description
Table1
Pin
NAME
1
SW
2
GND
3
FB
4
EN
5
IN
Description
Switching Pin. This is the drain of internal power MOSFET
switch. Connect the power inductor and output rectifier to SW.
Ground pin. Connect directly to local ground plane.
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
YB1521ST25
YB1521 MRev.1.1
Package Type
Supplied As
Package Marking
SOT23-5
3000 Units Tape & Reel
Y521
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YB1521
High Power Step-Up DC-DC Converter & WLED Driver
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
(Note 2)
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.
YB1521 MRev.1.1
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YB1521
High Power Step-Up DC-DC Converter & WLED Driver
Electrical Characteristics
Table4
(VIN=5V, VEN=5V, TA=25°C, unless otherwise noted.)
Parameters
Symbol
Test Conditions
MIN
TYP
MAX
Units
2.5
5
5.5
V
Input Voltage Range
VIN
Quiescent Current
IQ
VFB=0.3V
0.2
0.8
mA
Shutdown Current
ISD
VEN=0V, IOUT = 0mA
0.1
1
µA
Feedback Voltage
VFB
IOUT = 260mA, VOUT =
10.5V
200
220
mV
0.1
µA
FB Input Bias Current
VFB = 0.2V
Switch On-Resistance
RDSON
Maximum Duty Cycle
DTMX
Switching Frequency
FSW
EN Threshold
VENH
VEN Rising, VIN = 5V
EN Threshold
VENL
VEN Rising, VIN = 2.5V
VFB = 0V
EN Dimming Frequency
Switch Current Limit
Under Voltage Lock Out
180
IILM
UVLO
0.4
Ω
85
92
%
1
1.3
1.6
MHz
1
1.5
2
V
0.8
20
50
KHz
1
1.6
A
VIN Rising
2.25
UVLO Hysteresis
2.45
100
Over Voltage Protection
OVP
Thermal Shutdown
TSD
YB1521 MRev.1.1
V
16
The Hysteresis = 20℃
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18
160
V
mV
22
V
℃
4
YB1521
High Power Step-Up DC-DC Converter & WLED Driver
Typical Performance Characteristics
Steady State Operation
Startup Waveforms
VIN =5V, 39 LEDS, 260mA
VIN =5V, 39 LEDS, 260mA
Startup Waveforms into an Open Load
VIN =5V, 39 LEDS, 260mA
YB1521 MRev.1.1
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YB1521
High Power Step-Up DC-DC Converter & WLED Driver
Functional Block
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
YB1521 MRev.1.1
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:
ILED = 200mV / R1.
The maximum LED current set initially can
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YB1521
High Power Step-Up DC-DC Converter & WLED Driver
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
controlling PW M signal.
YB1521
EN
FB
Figure 5: PWM Dimming Control Using a Logic
YB1521
FB
R1
20K
R2
80K
R3
20K
0.1uF
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
Signal
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.
YB1521
FB
R1
80K
R2
20K
VDC
Diode Selection
Figure 6: Dimming Control Using a DC Voltage
YB1521 MRev.1.1
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
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YB1521
High Power Step-Up DC-DC Converter & WLED Driver
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
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YB1521
High Power Step-Up DC-DC Converter & WLED Driver
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
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