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 www.yobon.com.tw 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 www.yobon.com.tw 2 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 www.yobon.com.tw 3 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℃ www.yobon.com.tw 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 www.yobon.com.tw 5 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 www.yobon.com.tw 6 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 www.yobon.com.tw 7 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 www.yobon.com.tw 8 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 www.yobon.com.tw 9