YB1517 - Yobon

YB1517
Step-up DC-DC Converter & White LED Driver
Description
Features
The YB1517 is a Current-mode PWM
step-up DC-DC converter. It can drive up to
18V in 20mA output current conditions
while Vin at 3.0V and 20V at 3.5Vin. The
900 KHz switching frequency allows it to
work with tiny external components,
therefore minimize the footprint and cost in
space consideration products.
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One of the major applications for YB1517
is in the dc to dc converter and OLED
power supply and TFT panel power supply.
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When using YB1517 for white LED driving,
it is not recommended to control LED
brightness by applying a PWM signal to the
CTRL pin, because the built-in soft-start
circuit might interfere the start-up operation
of YB1517 and cause lower brightness. It
operates as current source to drive up to 6
white LEDs in series at 3.3V input. 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.
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900KHz Current-mode PWM Converter
Built-in Internal Switch
Adjustable Output Voltage up to 20V
2.7V to 16V Input Range
<1uA Shutdown Current
Internal Soft Start
Drives up to 6 White LEDs
Tiny Inductor and Capacitors Allowed
Over Voltage Protection 30V
Small 5-Lead SOT-23 Package
220mV Low Reference Voltage
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Green package (RoHS) available
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Applications
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LCD Display Module
White LED Backlighting
PDAs, GPS Terminals
Digital Cameras
Cellular Phone
Electronic Books
Portable Applications
YB1517 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
YB1517 Rev.1.4
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YB1517
Step-up DC-DC Converter & White LED Driver
Pin Configuration
SW
1
GND
2
FB
3
5
VIN
4
CTRL
SOT23-5
Figure 3: Pin Configuration
Pin Description
Table 1
Pin
Name
1
SW
2
GND
3
FB
4
CTRL
5
VIN
Description
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.
Ground Pin. Connect directly to local ground plane.
Feedback Pin. Reference voltage is 220mV. When connecting 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
Table 2
Order Number
Package Type
Supplied As
Package Marking
YB1517ST25
SOT23-5
3000 units Tape & Reel
Y58 F
YB1517 Rev.1.4
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YB1517
Step-up DC-DC Converter & White LED Driver
Absolute Maximum Ratings (Note 1)
VIN..........................................................20V
SW Voltage .............................................24V
FB Voltage ................................................5V
CTRL Voltage............................................5V
Maximum Junction Temp, TJ (note) ....... 150°C
Lead Temperature (Soldering 10 sec) ...... 250°C
Internal Power Dissipation, PD ..............0.4W
ESD Susceptibility (HBM)………………..2KV
ESD Susceptibility (MM)………………...200V
Recommended Operating Conditions
(Note 2)
Operating Temperature.........-40°C to 85°C
Supply Voltage......................... 2.7V to 16V
SW Voltage...........................................20V
Thermal Information
θJA…………………………………………………….. 220°C/W..
(Note 3)
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.
YB1517 Rev.1.4
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3
YB1517
Step-up DC-DC Converter & White LED Driver
Electrical Characteristics
Table 3
(VIN = 3.3V, L=22μH, CIN = 1μF, COUT = 4.7μF, TA=25°C, unless otherwise noted.)
Description
Symbol
Test Conditions
MIN
TYP
2.7
MAX
Units
16
V
Input Voltage Range
VIN
Quiescent Current
IQ
VFB = 0.5V
1.5
1.7
mA
Shutdown Current
ISD
CTRL = 0V
0.3
1
μA
Feedback Voltage
VFB
IOUT = 20mA,VOUT = 6V
Circuit of Figure 2
210
220
230
mV
Switch Current Limit
ICL
85% duty cycle
850
900
1000
mA
FB Pin Bias Current
IB
Switching Frequency
FSW
850
Maximum Duty Cycle
DMAX
85
Minimum Duty Cycle
DMIN
20
Switch Vcesat
VSAT
At ISW = 200mA
Switch Leakage Current
ILKG
CTRL = 0.5V
VCTRL for Full LED Current
VCTL
CTRL Pin Bias Current
ICTL
Over Voltage Protection
OVP
Over Thermal Protection
OTP
40% duty cycle
400
VFB = 220mV
Full On
900
mA
1
μA
950
KHz
%
25
%
180
mV
1
μA
1.7
V
Full Off
0.3
CTRL = 2V
40
28
30
160
V
μA
35
V
°C
Note :
Absolute maximum ratings are limits beyond which damage to the device may occur. The maximum allowable,
power dissipation at any ambient temperature is calculated using: PD(MAX)= [TJ(MAX)-TA]/θJA .
YB1517 Rev.1.4
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YB1517
Step-up DC-DC Converter & White LED Driver
Typical Performance Characteristics
YB1517 Rev.1.4
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YB1517
Step-up DC-DC Converter & White LED Driver
YB1517 Rev.1.4
www.yobon.com.tw
6
YB1517
Step-up DC-DC Converter & White LED Driver
YB1517 Rev.1.4
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YB1517
Step-up DC-DC Converter & White LED Driver
Function Block
Figure 4: YB1517 Block Diagram
Operation
Application Information
The YB1517 uses a constant frequency,
current mode control scheme to regulate
the output voltage. Its operation can be
understood by referring to the block
diagram in Figure 4. 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.
Soft Start and Current Limit
The internal soft start circuit minimizes the
inrush current during turning on YB1517.
The maximum switch current is limited to
about 900mA by the chip.
YB1517 Rev.1.4
Over Voltage Protection
The YB1517 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 YB1517
will then switch to a high duty cycle
resulting in a high output voltage, which
may cause SW pin voltage to exceed its
maximum 24V rating. The YB1517 will
shutdown automatically until input condition
changes to bring it out of the shutdown
mode.
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YB1517
Step-up DC-DC Converter & White LED Driver
Inductor Selection
A 22μH inductor is recommended for most
applications to the dc to dc converter and
OLED supply and TFT panel power supply.
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
Choose low ESR capacitors for the output
to minimize output voltage ripple. Multilayer
capacitors are a good choice for this as well.
A 4.7μF capacitor is sufficient for most
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
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
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.
in Figure 1, must be placed close to the IC.
Figure 5: Typical Application Circuit
YB1517 Rev.1.4
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YB1517
Step-up DC-DC Converter & White LED Driver
Package Information (SOT23-5)
milimeters
Inches
MIN.
MAX.
MIN.
MAX.
A
0.95
1.45
.037
.057
A1
0.05
0.15
.002
.006
A2
0.90
1.30
.035
.051
b
0.30
0.50
.0118
.019
C
0.08
0.20
.0031
.0078
D
2.84
3.00
.1118
.118
E
1.50
1.70
.059
.0669
E1
2.60
3.00
.102
.118
e
0.95 BSC.
.0374 BSC.
e1
1.90 BSC.
.0748 BSC.
L
0.35
0.55
.0137
.0216
L1
0.10 BSC.
.0039 BSC.
L2
0.60 REF.
.0236 REF.
t
0°
8°
0°
8°
NOTICE:
y The information described herein is subject to change without notice.
y Yobon does not assume any responsibility for use of any circuitry or applications described herein, nor
does it convey any patent license.
YB1517 Rev.1.4
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