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APPLICATION NOTE
S3F84A5
An LED Lighting System
January 2010
Revision 0.00
Confidential Proprietary of Samsung Electronics Co., Ltd
Copyright © 2010 Samsung Electronics, Inc. All Rights Reserved
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Important Notice The information in this publication has been carefully "Typical" parameters can and do vary in different checked and is believed to be entirely accurate at the applications. All operating parameters, including time of publication. Samsung assumes no "Typicals" must be validated for each customer responsibility, however, for possible errors or application by the customer's technical experts. omissions, or for any consequences resulting from the Samsung products are not des
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Revision History Revision No. Date Description Author(s) 0 Jan. 20, 2010 - Initial draft Wei Ningning
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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 ..............................................................
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List of Figures Figure Title Page Number Number Figure 1-1 S3F84P4 Pin Assignment.....................................................................................................................7 Figure 1-2 Simplified Buck Circuit..........................................................................................................................9 Figure 1-3 Current on load .....................................................................................................
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List of Tables Table Title Page Number Number Table 4-1 System validation of efficiency.............................................................................................................16 Table 5-1 BOM list of Key Circuit .........................................................................................................................17
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S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 1 OVERVIEW OF HPLED LIGHTING CONTROL SYSTEM 1 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 ra
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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/ 3.9V) Supports Configurable RC (1M/ 8MHz @5V) Supports six IOs (maximum) when using internal LVR
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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. At this time, since the coil will have inertia to keep the current direction, the load still can be powered with a fr
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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. Even a slight change of voltage migh
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S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 2 HARDWARE IMPLEMENTATION 2 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. Brightness can be obtained by changing the PWM duty cycle
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S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 2 HARDWARE IMPLEMENTATION 2.2 COMPONENTS SELECTION Assume the following two conditions: V (V I 1ohm) 3.5 0.35 3.85V OFW FW VV 5 I If non-divided system clock is selected as the clock source of the 6+6 PWM, its base frequency f OSC 125KHz 6 2 is . 2.2.1 SELECT THE INDUCTANCE (L1) FOR THE REQUIREMENT OF CURRENT RIPPLE D () VV IO V f PWM L 1 I I ripple T 3.85 LI (5 3.85) 7.084 1 ripple 5 125K Lu 100H 1 Therefore, 20% cu
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S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 3 SOFTWARE IMPLEMENTATION 3 SOFTWARE IMPLEMENTATION Figure 3-1 shows the software implementation. Initialization ADC sampling Decrease PWM Value > max? duty cycle Increase PWM Vale < min? 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. Therefore, any
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S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 3 SOFTWARE IMPLEMENTATION Start Start Y Y PWMEX>= PWMEX>=100B? 11111100B? N N PWMEX = 0xFF PWMEX = 0 PWMEX - =1 PWMEX + = 1 PWMDATA - =1 PWMDATA + =1 End End Decrease PWM duty cycle Increase PWM duty cycle Figure 3-2 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 8MHz PWM 125KHz 6 f 8MHz PWM 264 is, when . The overall cycle is still 12-bit to make the 12-
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S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 4 SYSTEM VALIDATION 4 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 Waveform for HPLED forward voltage and current V s () VV fd s R s efficiency (I I) V VV 5 ps MCU ps ps and Based on the above formulas, Table 1 shows the values of Ips, Imcu, Vfd, Vs, and efficiency (%). Samsung Confidential 15
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S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 4 SYSTEM VALIDATION Table 4-1 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) 18 19 18 19 18 19 18 19 18 19 (MCU 供电LED) 3.82 3.6 3.85 3.60 3.86 3.6 3.90 3.59 3.90 3.65 Vfd V ） 357 340 359 340 351 340 359 341 358 360 Vs mV ） 87.68 81.6 87.03 82.5 87.35 81.6 87.37 80.95 87.45 81.11 Efficiency （% ） NOTE: BD1 and BD2 represent two board
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S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 5 APPENDIX 5 APPENDIX 5.1 BOM LIST OF KEY CIRCUIT Table 5-1 shows the BOM list of key circuit. Table 5-1 BOM list of Key Circuit Reference Description Manufacturer Part number R1 1K ohms R2 10 ohms Rs Current sensing Resistor WSR21R000FEA VISHAY C1 104 C2 47uF Tantalum Capacitor C3 2nF C4 100uF R4 33K ohms Q1 HEXFET Power MOSFET IR IRF9540 D1 Schottky Diode IN5819 L1 100 uH inductance TDK VLF12060-101M1R0 HPLED 1W
