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. 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 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. 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 Green package (RoHS) available Applications 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 www.yobon.com.tw 1 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 www.yobon.com.tw 2 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 www.yobon.com.tw 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 www.yobon.com.tw 4 YB1517 Step-up DC-DC Converter & White LED Driver Typical Performance Characteristics YB1517 Rev.1.4 www.yobon.com.tw 5 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 www.yobon.com.tw 7 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. www.yobon.com.tw 8 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 www.yobon.com.tw 9 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 www.yobon.com.tw 10