www.fairchildsemi.com AN-7701 FL7701 Design Tool Flow Example: Overview This document is intended to provide in-depth guidance to using the Fairchild Design Tool for FL7701. Use the Design Tool with the product datasheet. Step-by-Step 1. Enter the input voltage. 2. Enter the LED characteristics (forward voltage). 3. Enter the LED counts. 4. Enter the LED peak current. 5. Enter the LED rms current. 6. Enter the target system efficiency. 7. Enter the desired switching frequency. 220V Input Voltage 3.5V Forward Voltage 10 LEDs in series 500mApk 300mArms 85% efficiency 45kHz Table 1. Design Values to Enter Item Maximum Input Voltage LED Forward Voltage Number of LEDs LED Peak Current LED rms Current Efficiency Switching Frequency Value Units VIN.MAX.AC= Vf= Number_LED= ILED.peak= IVAE_rms= Eff= fSW= 220 3.5 10 500 300 85 45 V V EA mA mA % kHz Figure 2. Output Capacitor Selection Guide Plot © 2011 Fairchild Semiconductor Corporation Rev. 1.0.1 • 3/21/12 www.fairchildsemi.com AN-7701 APPLICATION NOTE Calculation Results Table 2. Table 3. Internal Process Item Current Ripple LED Minimum Current LED Current Ave. Peak Minimum Duty Cycle Output Voltage Value Units I= 151.5 IMIN= 348.53 (IMAX + IMIN ) / 2= 424 DMIN= 13.237 VO= 35.000 Results Item Inductance Current Sensing Resistor Frequency Setting Resistor mA mA mA % V Table 4. Value Units LM= 4.455 RCS= 1.000 Rf= 44.919 mH Ω kΩ Expected Power Item Expected Output Power Expected Input Power Value Units POUT= 10.500 PIN= 12.353 W W Figure 3. Output Capacitor Selection Guide Plot and Table Notes: 1. Inductance. 2. Sensing resistor value (Rcs). 3. RT value. 4. Can omit RT, when fSW is close to 45kHz. © 2011 Fairchild Semiconductor Corporation Rev. 1.0.1 • 3/21/12 www.fairchildsemi.com 2 AN-7701 APPLICATION NOTE Related Resources Locate the Design Tool at: http://www.fairchildsemi.com/design_tools/led-driver-design-tool/ Consult the product datasheet at: FL7701 — Smart Non-isolated PFC Buck LED Driver Follow us on Twitter at: twitter.com/fairchildSemi View product and company videos, listen to podcasts, and comment on our blog at: www.fairchildsemi.com/engineeringconnections Visit us on Facebook at: www.facebook.com/FairchildSemiconductor DISCLAIMER FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION, OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS. LIFE SUPPORT POLICY FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR CORPORATION. As used herein: 1. 2. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, or (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in significant injury to the user. © 2011 Fairchild Semiconductor Corporation Rev. 1.0.1 • 3/21/12 A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. www.fairchildsemi.com 3