APPLICATION NOTE S3F84A5 An LED Lighting System January 2010 Revision 0.00 Confidential Proprietary of Samsung Electronics Co., Ltd Copyright © 2010 Samsung Electronics, Inc.
Important Notice The information in this publication has been carefully checked and is believed to be entirely accurate at the time of publication. Samsung assumes no responsibility, however, for possible errors or omissions, or for any consequences resulting from the use of the information contained herein.
Revision History Revision No. Date 0 Jan.
Table of Contents 1 Overview of HPLED Lighting Control System ............................................7 1.1 Pin Assignment in S3F84P4 ........................................................................................................................7 1.2 Key Features of S3F84P4............................................................................................................................8 1.3 System Principle .............................................................................
List of Figures Figure Number Title Page Number Figure 1-1 Figure 1-2 Figure 1-3 Figure 1-4 S3F84P4 Pin Assignment.....................................................................................................................7 Simplified Buck Circuit ..........................................................................................................................9 Current on load ...............................................................................................................
List of Tables Table Number Title Page Number Table 4-1 System validation of efficiency.............................................................................................................16 Table 5-1 BOM list of Key Circuit .........................................................................................................................
S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 1 1 OVERVIEW OF HPLED LIGHTING CONTROL SYSTEM OVERVIEW OF HPLED LIGHTING CONTROL SYSTEM A light-emitting diode (LED) is a semiconductor light source that presents several advantages over traditional light (like incandescent) sources such as lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliance. It renders “green” light and does not contribute towards material pollution or radiations.
S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 1 OVERVIEW OF HPLED LIGHTING CONTROL SYSTEM 1.2 KEY FEATURES OF S3F84P4 The key features in S3F84P4 include: 4 kbyte Flash ROM or 208 Byte SRAM 6+6 PWM x 1 10-bit ADC x 4 8-bit Basic Timer (can be used as watchdog timer) 16-bit Timer0 (can be used as Timer A or B, the two 8-bit Timers ) EXINT X 2 Supports Configurable LVR (2.2/ 3.0/ 3.
S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 1 OVERVIEW OF HPLED LIGHTING CONTROL SYSTEM 1.3.1 BUCK CIRCUIT Figure 1-2 Simplified Buck Circuit Buck circuit works when a switch signal turns on the transistor (Q). The DC power then starts to charge the coil (L). When the current reaches a predefined level, change the transistor state from On to Off using the switch signal.
S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 1 OVERVIEW OF HPLED LIGHTING CONTROL SYSTEM 1.3.3 CONSTANT CURRENT CONTROL Refer to the HKP-D1W1 datasheet to see the relationship of forward voltage, forward current, and relative luminous flux. Figure 1-4 HKP-D1W1 Forward Voltage, Forward Current, and Relative Luminous Flux As shown in Figure 1-4, describing the luminous flux as a function of current is better than describing it as a function of voltage.
S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 2 2 HARDWARE IMPLEMENTATION HARDWARE IMPLEMENTATION 2.1 SYSTEM DIAGRAM AND CIRCUIT Figure 2-1 Control Circuit As shown in Figure 2-1, the Buck Circuit comprise of Q1, L1, D1, and C2. The output of PWM turns on/off the transistor (Q1). The current over HPLED is sensed by a 1ohm power resistor. It then goes into S3F84P4’s ADC module after passing through a filter composed of R4 and C3.
S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 2 HARDWARE IMPLEMENTATION 2.2 COMPONENTS SELECTION Assume the following two conditions: VO (VFW I FW 1ohm) 3.5 0.35 3.85V VI 5V If non-divided system clock is selected as the clock source of the 6+6 PWM, its base frequency f OSC 125 KHz 6 is 2 . 2.2.1 SELECT THE INDUCTANCE (L1) FOR THE REQUIREMENT OF CURRENT RIPPLE L1 V I T (VI VO ) D f PWM I ripple L1 I ripple (5 3.85) 3.85 7.
S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 3 3 SOFTWARE IMPLEMENTATION SOFTWARE IMPLEMENTATION Figure 3-1 shows the software implementation. Initialization ADC sampling Value > max? Decrease PWM duty cycle Vale < min? Increase PWM duty cycle Figure 3-1 Software Implementation Diagram Since the PWM in S3F84P4 is 6+6 type, it affects the software in two ways. Way to change the PWM duty cycle: The duty cycle is the result of both the register values of PWMDATA and PWMEX.
S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 3 SOFTWARE IMPLEMENTATION Start Start Y PWMEX>= 11111100B? PWMEX>=100B? N PWMEX = 0xFF PWMDATA - =1 N PWMEX - =1 End PWMEX + = 1 PWMEX = 0 PWMDATA + =1 End Decrease PWM duty cycle Increase PWM duty cycle Figure 3-2 Y Way to change PWM duty cycle Change rate of PWM duty cycle: If PWM in S3F84P4 is 6+6 type, the PWM basic frequency is 6-bit, that f PWM 8MHz 125KHz 6 f 8MHz .
S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 4 4 SYSTEM VALIDATION SYSTEM VALIDATION Figure 4-1 shows the current ripple and voltage ripple test waveform. Red and blue colors specify the current and voltage, respectively. Figure 4-1 Vs Rs efficiency ( I ps I MCU ) V ps Waveform for HPLED forward voltage and current (V fd Vs ) and V ps 5V Based on the above formulas, Table 1 shows the values of Ips, Imcu, Vfd, Vs, and efficiency (%).
S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) Table 4-1 4 SYSTEM VALIDATION System validation of efficiency #1 #2 #3 #4 #5 BD1 BD2 BD1 BD2 BD1 BD2 BD1 BD2 BD1 BD2 Ips (power supply) (mA) 300 288 306 285 300 288 309 290 308 304 Imcu (mA) (MCU供电LED) 18 19 18 19 18 19 18 19 18 19 Vfd V） 3.82 3.6 3.85 3.60 3.86 3.6 3.90 3.59 3.90 3.65 Vs mV） 357 340 359 340 351 340 359 341 358 360 87.68 81.6 87.03 82.5 87.35 81.6 87.37 80.95 87.45 81.
S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 5 5 APPENDIX APPENDIX 5.1 BOM LIST OF KEY CIRCUIT Table 5-1 shows the BOM list of key circuit.
