LESHAN RADIO COMPANY, LTD. LR256 White LED Step-Up Converter LR256 is a step-up DC/DC converter specifically designed to drive white LED with a constant current. It can drive two,three,or four LEDS. It switches at 1.2MHz and use tiny external components. The output capacitor can be as small as 0.22uF,which can save space and cost versus alternative solutions. Feedback ¾ ¾ ¾ ¾ ¾ ¾ ¾ ¾ Fast 1.2MHz Switching Frequency Requires Only 0.22uF Output Capacitor Inherently Matched LED Current High Efficiency: 85% Typical 2.5V to 10V VIN ranges Drives Up to Four series LEDs with a Li-lon cell Uses Very Tiny Inductors SOT-25 Package voltage is as low as 95mV. Absolute maximum ratings Parameter symbol value unit Supply Voltage VIN 10 V Feedback Voltage FB 10 V Switch Voltage SW 20 V CE Voltage VCE 10 V Operating temperature range Topr -25 to +70 ℃ Storage temperature range Rstg -55 to +150 ℃ Junction temperature Tj 125 ℃ Pin name Description 1 Symbol Description Symbol 5 5：Supply 2 3 1：Switch SW VIN Voltage 4 2：GND GND 3：Feedback FB 4：Start-Up CE 1/8 LESHAN RADIO COMPANY, LTD. LR256 Block Diagram PIN1(SW) PWM CONTROL 2 Fosc CURRENT SENSE + 1 SLOPE COMP + 0 - PIN5(Vin) 2 0 2 VREF 1 1 2 PIN2(GND) + 1 2 PIN4 1 SHUTDOWN gm D256 PIN3(FB) 2/8 LESHAN RADIO COMPANY, LTD. LR256 Electrical Characteristics Tamb = 25℃, VIN=3V，VCE=3V,unless otherwise specified. Parameter Test Conditions / Pins Min Minimum Operating Voltage Type Max 2.5 Unit V Maximum Operating Voltage 10 V ISW=100mA, Feedback Voltage 86 95 104 mV 50 100 200 nA 1.9 2.5 mA 0.1 1 uA 1.6 MHz Duty Cycle=66% FB Pin Bias Current Supply Current VCE=0V Switching Frequency 0.8 1.2 Maximum Duty Cycle 85 90 % 320 mA mV Switch Current Limit Switch VCESAT ISW =250mA 350 Switch Leakage Current VSW=5V 0.01 CE Voltage High 5 uA 1.5 V CE Voltage Low 0.4 CE Pin Bias Current V 65 uA Typical Application L1 1 HI 2 22uH VCC PIN1(SW) D4 1 2 D1 PWM CONTROL C1 2 C2 Fosc 0.22u CURRENT SENSE + 0 0 - PIN5(Vin) 2 D1 1 SLOPE COMP + 2 VREF 1 1 2 PIN2(GND) 1 2 D1 + - 1u gm 1 SHUTDOWN PIN3(FB) 1k R1 R PIN4(CE) 3/8 LESHAN RADIO COMPANY, LTD. LR256 Analog Voltage Light Control L1 1 HI 2 22uH VCC PIN1(SW) D4 1 2 D1 PWM CONTROL C1 2 1u C2 Fosc 0.22u CURRENT SENSE + 0 0 - PIN5(Vin) 2 D1 1 SLOPE COMP + 2 VREF 1 1 2 PIN2(GND) D1 + 1 2 gm 1 5K SHUTDOWN R1 R PIN3(FB) PIN4(CE) 90K HI VDC Logic Voltage Light Control L1 1 HI 2 22uH VCC PIN1(SW) D4 1 2 D1 PWM CONTROL C1 1u 2 C2 Fosc 0.22u CURRENT SENSE + 0 0 - PIN5(Vin) 2 D1 1 SLOPE COMP + 2 VREF 1 1 2 PIN2(GND) D1 + 1 2 gm 1 HI SHUTDOWN PWM PIN3(FB) 1k R1 R PIN4(CE) 4/8 LESHAN RADIO COMPANY, LTD. LR256 Figure Iq(mA) Iq Vs T 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -50 100 25 0 2 4 6 8 10 Vin(V) Swich Frequency Vs T Swich Frequency（MHz） 1.4 1.2 1 0.8 0.6 0.4 0.2 0 -25 0 25 50 75 100 T（°C） 5/8 LESHAN RADIO COMPANY, LTD. LR256 η（%） η VS T 84.5 84 83.5 83 82.5 82 81.5 81 80.5 80 ILED=10mA ILED=15mA ILED=20mA -25 0 25 50 75 100 T（°C） η（%） Drive 2LED 86 84 82 80 78 76 74 72 70 Vin=3.6V Vin=3V 0 10 20 ILED(mA) 30 40 6/8 LESHAN RADIO COMPANY, LTD. LR256 Drive 3LED 90 η（%） 85 80 Vin=3V Vin=3.6V 75 70 65 60 0 5 10 ILED（mA） 15 20 7/8 LESHAN RADIO COMPANY, LTD. LR256 SOT25 Diagram Symbol A A1 B b C D E H L min 0.787 1.397 0.250 2.591 2.692 0.838 0.080 0.300 Dimension(in mm) max 1.450 0.152 1.803 0.559 2.997 3.099 1.041 0.254 0.610 Dimension(in Inch) min max 0.031 0.057 0.006 0.055 0.071 0.010 0.022 0.102 0.118 0.106 0.122 0.033 0.041 0.003 0.010 0.012 0.024 8/8