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| YB1520 High Power Step-up DC-DC Converter, White LED Driver Description The YB1520 is a step-up DC-DC converter; operates as current source to drive up to 9 white LEDs in series or 30 white LEDs in parallel/series configuration. 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 YB1520 switches at a fixed frequency of 700KHz, 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 YB1520 can drive up to 9 white LEDs from a single Li-Ion battery and drive up to 30 white LEDs from a 5V. 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 50KHz to the CTRL pin. YB1520 has integrated 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 Built-in internal switch Adjustable output voltage up to 35V 2.7V to 16V input range <1uA shutdown current High efficiency Drives up to 30 white LEDs in Parallel/series Over voltage protection Small 5-Lead SOT-23 package Applications LCD Display Module White LED Backlighting PDAs, GPS terminals Digital Cameras Cellular Phone Electronic Books Portable Applications Typical Application Circuit Figure 1: Typical Application Circuit YB1520 MRev.1.2 www.yobon.com.tw 1 YB1520 High Power Step-up DC-DC Converter, White LED Driver 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 200mV. 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 3 FB 4 CTRL 5 VIN Ordering Information Order Number YB1520ST25 Supplied as 3000 units Tape & Reel Package Marking Y52M YB1520 MRev.1.2 www.yobon.com.tw 2 YB1520 High Power 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 (not 2)...................150C Lead Temperature (Soldering 10 sec) ................300C Thermal Resistance............................................195C Recommended Operating Conditions Operating Temperature (note 3) ................ -40C~85C Supply Voltage............................................. 2.5V~16V SW Voltage ............................................................30V Electricity Characteristics (TA=25C, Vin=3.3V, Cin=1uF Cout=10uF unless otherwise noted) Symbol Vin IQ (Quiescent Current) VFB ICL ILIM IB FRSW DTMX DTMN VSAT ILKG VCTL ICTL OVP JA 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 Thermal Resistance Test Conditions Vfb = 0.3V CTRL = 0V Iout=20mA,Vout=12.5V Circuit of Figure 1 100% Duty Cycle 40% Duty Cycle Vfb=200mV Min 2.7 1.2 Typ 1.5 0.3 Max 16 1.7 1 220 950 20 720 85 Units V mA uA mV mA mA uA KHz % % mV A 180 850 2 680 200 900 600 10 700 20 At Isw = 200mA Ctrl = 0.3V Full On Full Off Ctrl = 2V 120 1 1.7 0.2 20 34 220 25 1.8 0.3 V V A V C/W 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, JA , and the ambient temperature. The maximum allowable, power dissipation at any ambient temperature is calculated using: PD(MAX)= [TJ(max)-TA]/JA . Exceeding the maximum allowable power dissipation will cause excessive die temperature. All limits at temperature extremes are guaranteed via correlation using standard statistical methods YB1520 MRev.1.2 www.yobon.com.tw 3 YB1520 High Power Step-up DC-DC Converter, White LED Driver Typical Performance Characteristics EFFICIENCY 89% EFFICIENCY(%) 88% 87% 86% 85% 84% 4 4.5 5 VIN(V) 5.5 6 3S5P Output Ripple YB1520 MRev.1.2 www.yobon.com.tw 4 YB1520 High Power Step-up DC-DC Converter, White LED Driver Efficiency 90% EFFICIENCY(%) 88% 86% 84% 82% 4 4.5 5 VIN(V) 5.5 6 3S6P Output Ripple YB1520 MRev.1.2 www.yobon.com.tw 5 YB1520 High Power Step-up DC-DC Converter, White LED Driver EFFICIENCY 90% EFFICIENCY(%) 88% 86% 84% 82% 80% 4 4.5 5 VIN(V) 5.5 6 3S7P Output Ripple YB1520 MRev.1.2 www.yobon.com.tw 6 YB1520 High Power Step-up DC-DC Converter, White LED Driver Efficiency 90% EFFICIENCY(%) 88% 86% 84% 82% 80% 4 4.5 5 VIN(V) 5.5 6 3S8P Output Ripple YB1520 MRev.1.2 www.yobon.com.tw 7 YB1520 High Power Step-up DC-DC Converter, White LED Driver Efficiency 88% EFFICIENCY(%) 86% 84% 82% 80% 4 4.5 5 VIN(V) 5.5 6 3S9P Output Ripple YB1520 MRev.1.2 www.yobon.com.tw 8 YB1520 High Power Step-up DC-DC Converter, White LED Driver Efficiency 88% EFFICIENCY(%) 86% 84% 82% 80% 4 4.5 5 VIN(V) 5.5 6 3S10P Output Ripple YB1520 MRev.1.2 www.yobon.com.tw 9 YB1520 High Power Step-up DC-DC Converter, White LED Driver Efficiency 84% EFFICIENCY(%) 82% 80% 78% 76% 3 3.5 4 4.5 VIN(V) 5 5.5 6 9S Output Ripple YB1520 MRev.1.2 www.yobon.com.tw 10 YB1520 High Power Step-up DC-DC Converter, White LED Driver EFFICIENCY 85% EFFICIENCY(%) 84% 83% 82% 81% 80% 79% 4 4.5 5 VIN(V) 5.5 6 8S3P Output Ripple YB1520 MRev.1.2 www.yobon.com.tw 11 YB1520 High Power Step-up DC-DC Converter, White LED Driver Efficiency 86% EFFICIENCY(%) 84% 82% 80% 78% 4 4.5 5 5.5 VIN(V) 6 6.5 7 9S3P Output Ripple YB1520 MRev.1.2 www.yobon.com.tw 12 YB1520 High Power Step-up DC-DC Converter, White LED Driver Typical Performance Characteristics Drive Switch Saturation Voltage(Vcesat) 160 Saturation Voltage(mV) Switching Frequency (KHz) 730 725 Switching Frequency 140 120 100 80 60 0 50 100 150 200 250 300 Switch Current(mA) 720 715 710 705 700 695 0 20 40 60 80 100 120 TEMPERATURE (C) Switch Leakage Current 1 0.9 0.8 0.7 0.6 0.5 2 4 6 8 10 Vin(V) 12 14 16 Supply current test 2.5 2 Iin ( m A ) 1.5 1 0.5 2 4 6 8 10 Vin (V) 12 14 16 I(uA ) YB1520 MRev.1.2 www.yobon.com.tw 13 YB1520 High Power Step-up DC-DC Converter, White LED Driver Switching Waveform YB1520 MRev.1.2 www.yobon.com.tw 14 YB1520 High Power Step-up DC-DC Converter, White LED Driver Functional Block Figure 3: YB1520 Block Diagram Operation The YB1520 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. 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 error amplifier's output increases, more current is delivered to the output; if it decreases, less current is delivered. Application Information Inrush Current The maximum switch current is limited to about 900 mA by the chip Typically, A larger Cout will increase the duration of high current. However, when Vin is first connected, an even larger current can flow into Cout. This occurs when the SW pin is open circuit and the Cout voltage changes from 0V to Vin in a few microseconds. Because the duration of this large current is short, it will usually not cause problems. If this current is not desirable, an external soft-start circuit can be added to significantly reduce this inrush current. YB1520 MRev.1.2 www.yobon.com.tw 15 YB1520 High Power Step-up DC-DC Converter, White LED Driver LED Current and Dimming Control The LED's current is set by a resistor connected at FB pin to GND using: 200mV I LED = RLED 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 5 respectively. Using the above different scheme, the LED current can be controlled from 20% to 80% to its maximum value. PWM Signal(1KHz,2Vp-p,duty 20%~80%) Over Voltage Protection The YB1520 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 YB1520 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 YB1520 will shutdown automatically until input condition changes to bring it out of the shutdown mode. Inductor Selection A 47uH inductor is recommended for most applications to drive more than 9 LEDs in serials and 33uH inductor is recommended for drive 30 LEDs in serials/parallel. 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. Figure 4. Dimming Control Using a DC Voltage Figure 5. Dimming Control Using a Filtered YB1520 MRev.1.2 www.yobon.com.tw 16 YB1520 High Power Step-up DC-DC Converter, White LED Driver 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 47uF 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 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. YB1520 MRev.1.2 www.yobon.com.tw 17 YB1520 High Power 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. YB1520 MRev.1.2 www.yobon.com.tw 18 |
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