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YB1517
Step-up DC-DC Converter & White LED Driver
Description
The YB1517 is a Current-mode PWM step-up DC-DC converter. It can drive up to 18V at 3.0V input and 30V at 5.0V input. The 1 MHz switching frequency allows it to work with tiny external components, therefore minimize the footprint and cost in space consideration products. One of the major applications for YB1517 is in the dc to dc converter and OLED power supply and TFT panel power supply. 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 5 white LEDs in series at 3.0V input and up to 8 white LEDs at 5.0V 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. 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.
Features
* * * * * * * * * * 900 KHz current-mode PWM converter Built-in internal switch Adjustable output voltage up to 30V 2.7V to 16V input range <1uA shutdown current Internal Soft Start Drives up to 5 white LEDs Tiny Inductor and Capacitors allowed Small 5-Lead SOT-23 package 220mV Low Reference Voltage
Applications
* * * * * * * LCD Display Module White LED Backlighting PDAs, GPS terminals Digital Cameras Cellular Phone Electronic Books Portable Applications
Typical Application Circuit
YB1517 MRev.1.0
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YB1517
Step-up DC-DC Converter & White LED Driver
Pin Configuration
Figure 3 : YB1517 Pin Configuration
Pin Description
Table 1
Pin 1 2
NAME
Description
SW GND
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
3
FB
4
CTRL
5
VIN
Ordering Information
Table 2
Order Number YB1517ST25
YB1517 MRev.1.0
Supplied as 3000 units Tape & Reel
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Package Marking Y58 F
2
YB1517
Step-up DC-DC Converter & White LED Driver
Absolute Maximum Ratings
VIN ................................................................................. 20V SW Voltage .................................................................... 35V FB Voltage .......................................................................5V CTRL Voltage...................................................................5V Maximum Junction Temp,TJ (not 2) ............................150C Lead Temperature (Soldering 10 sec) .........................250C Thermal Resistance (SOT-25, JA) .......................250/W Internal Power Disspation (SOT-25, PD)...................... 0.4W
Recommended Operating Conditions
Operating Temperature (note 3) .........................-40C~85C Supply Voltage .................................................... 2.7 V~16V SW Voltage ....................................................................30V ESD Susceptibility (HBM).............................................. 2KV ESD Susceptibility (MM)...............................................200V
Electricity Characteristics
Table 3
(TA=25C, Vin=3.3V, L=22uH, Cin=1uF, Cout=4.7uF unless otherwise noted) Function Parameter Input Voltage Range Not Switching Shutdown Feedback Voltage Switch Current Limit FB Pin Bias Current Switching Frequency Maximum Duty Cycle Minimum duty cycle Switch Vcesat Switch Leakage Current VCTRL for Full LED current CTRL Pin Bias Current Over Voltage Protection At Isw = 200mA Ctrl = 0.5V Full On Full Off Ctrl = 2V 40 34 1.7 0.3 20 VFB = 0.5V CTRL = 0V Iout=20mA,Vout = 6V Circuit of Figure 2 100% duty cycle 40% duty cycle VFB=220mV 850 900 210 850 Test Conditions Min 2.7 1.2 1.5 0.3 220 900 400 1 950 85 25 180 1 Typ Max 16 1.7 1 230 1000 Units V mA uA mV mA mA uA KHz % % mV A V V A V
Symbol Vin IQ (Quiescent Current) VFB ICL IB FRSW DTMX DTMN VSAT ILKG VCTL ICTL OVP
JA
Thermal Resistance
220
C/W
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]/JA .
YB1517 MRev.1.0
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YB1517
Step-up DC-DC Converter & White LED Driver
Typical Characteristics
YB1517 MRev.1.0
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YB1517
Step-up DC-DC Converter & White LED Driver
YB1517 MRev.1.0
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5
YB1517
Step-up DC-DC Converter & White LED Driver
YB1517 MRev.1.0
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YB1517
Step-up DC-DC Converter & White LED Driver
Functional Block
Figure 3: YB1517 Block Diagram
Operation
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 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.
YB1517 MRev.1.0
Application Information
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 900 mA by the chip. 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 34V rating. The YB1517 will shutdown automatically until
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YB1517
Step-up DC-DC Converter & White LED Driver
input condition changes to bring it out of the shutdown mode. Inductor Selection A 22uH 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 4.7uF 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 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
YB1517 MRev.1.0 www.yobon.com.tw 8
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.
YB1517
Step-up DC-DC Converter & White LED Driver
Figure 4 : Typical Application Circuit
Figure 5 : TFT Panel Power Application Circuit
YB1517 MRev.1.0
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YB1517
Step-up DC-DC Converter & White LED Driver
Package Description
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.
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