Samsung S3F84A5 User Manual

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APPLICATION NOTE

S3F84A5

An LED Lighting System

January 2010

Revision 0.00

Confidential Proprietary of Samsung Electronics Co., Ltd

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.

Samsung reserves the right to make changes in its products or product specifications with the intent to improve function or design at any time and without notice and is not required to update this documentation to reflect such changes.

This publication does not convey to a purchaser of semiconductor devices described herein any license under the patent rights of Samsung or others.

Samsung makes no warranty, representation, or guarantee regarding the suitability of its products for any particular purpose, nor does Samsung assume any liability arising out of the application or use of any product or circuit and specifically disclaims any and all liability, including without limitation any consequential or incidental damages.

"Typical" parameters can and do vary in different applications. All operating parameters, including "Typicals" must be validated for each customer application by the customer's technical experts.

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S3F84A5 An LED Lighting System Application Note, Revision 0.00

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electric or mechanical, by photocopying, recording, or otherwise, without the prior written consent of Samsung Electronics.

Samsung Electronics Co., Ltd. San #24 Nongseo-Dong, Giheung-Gu Yongin-City, Gyeonggi-Do, Korea 446-711

TEL : (82)-(031)-209-4356 FAX : (82)-(031)-209-3262

Home Page: http://www.samsungsemi.com Printed in the Republic of Korea

Revision History

Revision No. Date Description Author(s)

0 Jan. 20, 2010 - Initial draft Wei Ningning

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 ..........................................................................................................................................8

1.3.1 Buck Circuit...........................................................................................................................................9

1.3.2 Summary ..............................................................................................................................................9

1.3.3 Constant Current Control....................................................................................................................10

2 Hardware Implementation ..........................................................................11

2.1 System Diagram and Circuit......................................................................................................................11

2.2 Components Selection...............................................................................................................................12

2.2.1 Select the Inductance (L1) for the Requirement of Current Ripple....................................................12

2.2.2 Select the Capacitance (C2) for the Requirement of Voltage Ripple.................................................12

3 Software Implementation............................................................................13

4 System Validation .......................................................................................15

5 Appendix......................................................................................................17

5.1 BOM List of Key Circuit..............................................................................................................................17

5.2 Appendix 2: Source Code..........................................................................................................................17

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.....................................................................................................................................9

Figure 1-4 HKP-D1W1 Forward Voltage, Forward Current, and Relative Luminous Flux...................................10

Figure 2-1 Control Circuit.....................................................................................................................................11

Figure 3-1 Software Implementation Diagram .....................................................................................................13

Figure 3-2 Way to change PWM duty cycle.........................................................................................................14

Figure 4-1 Waveform for HPLED forward voltage and current............................................................................15

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

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,

switching, and greater durability and reliance. It renders “green” light and does not contribute towards

faster material pollution or radiations. Usually, an LED can also be referred to as HPLED (high power LED) if the NRP (normal rated power) is greater than 1W. It can be driven at currents that vary from hundreds of mA to more than an ampere. LEDs can produce hundreds of lumens, and find extensive usage in lighting syste ms.

This do S3F84P4.

1.1 PIN ASSIGNMENT IN S3F84P4

Figure 1-1 shows the pin assignment in S3F84P4.

cument presents a simple HPLED lighting control system implemented with Samsung’s 8-bit MCU

Figure 1-1 S3F84P4 Pin Assignment

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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 and internal RC

1.3 SYSTEM PRINCIPLE

The two considerations for HPLED are:

1. Forward voltage

2. Constant control current Different LED applications have different characteristics. For instance, LEDs come in different colors. In some

cases, manufacturers of the LED applications might also differ. Even if the LED applications come from the same manufacturer, it can lead to differences in forward voltage. In such cases, constant voltage power cannot work.

Different LED applications should select different power suppliers according to its characteristics. For instance, by considering efficiency, switch module power supplier (SMPS) can be chosen for different LED applications. SMPS consists of Buck, Boost, or Buck-Boost circuits.



The duty cycl voltage, that is, .

The duty cycl

upply, that is, .

The duty cycl

ply and forward voltage.

sup

e of Buck circuit is . It is only used when the power supply is high

VV

e of Boost circuit is . It is only used when the forward voltage is higher than the power

VV

e of Buck-Boost circuit is . It can be used without considering the relationship of power





er than the forward

In this application, buck circuit is chosen to power a HKP-D1W1 white LED (forward voltage 3.5V) with a DC power source of 5V.

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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 cha rge 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 freewheeling diode until the switch signal turns on the transistor again. The resulting current is continuous but alternating (see

Figure 1-3 for more details).

Figure 1-3 Current on load

1.3.2 SUMMARY

The average current over load is determined by the duty cycle of switch signal.

  SMPS can lead to current ripple. But it could be alleviated by increasing the PWM frequency or coil

inductance value, or by adding extra filtering circuits.

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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 function of voltage. Even a slight change of voltage might lead to significant current shift. Therefore, constant current control is used in HPLED applications.

1-4, describing the luminous flux as a function of current is better than describing it as a

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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 transistor (Q1). The current over HPLED is sensed by a 1ohm power resisto r. 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 after comparing the actual sensin g value and target forward current. This application uses two external interrupts (“ENINT” and “GPIO” as shown in Figure keys to control the turn-on/off and brightness. A normal LED indicates the current brightness as full or half brightness.

2-1, the Buck Circuit comprise of Q1, L1, D1, and C2. The output of PWM turns on/off the

2-1) as

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S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 2 HARDWARE IMPLEMENTATION



2.2 COMPONENTS SELECTION

Assume the following two conditions:

( 1 ) 3.5 0.35 3.85

V V I ohm V 

OFWFW

VV

If non-divided system clock is selected as the clock source of the 6+6 PWM, its base frequency

OSC

125

KHz

2.2.1 SELECT THE INDUCTANCE (L1) FOR THE RE

ripple

3.85



5 125

100Lu H

()







 

ripple

Therefore, 20% current ripple means .

2.2.2 SELECT THE CAPACITANCE (C2) FOR THE RE

To reduce the voltage ripple and power loss, a capacitor with small ESR like Tantalum Capacitor should be chosen as C2. When ESL and ESR are negligible, then,

(5 3.85) 7.084

QUIREMENT OF CURRENT RIPPLE

QUIREMENT OF VOLTAGE RIPPLE





ripple

 

ripple

0.35*0.2 125

0.56

47Cu F

Therefore, 1% voltage ripple means . The free

wheeling diode should be a Schottky diode, as the system requires low turn-on voltage and fast switching.

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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

Value > max?

Vale < min?

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 increase or decrease in register from PWMDATA will not change the duty cycle. For more details on register PWMEX, refer to the S3F84P4 User’s Manual. Figure change the PWM duty cycle.

Decrease PWM

duty cycle

Increase PWM

duty cycle

3-2 shows the right way to

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S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 3 SOFTWARE IMPLEMENTATION



Start

PWMEX>=100B?

PWMEX = 0xFF PWMDATA - =1

End

Decrease 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

PWM

264

is,

resolution fully valid, that is, take effect after 0.512ms. Considering the AD conversion duration is 25us, duty cycle can be updated every 21 times of AD conversion.

MHz

PWMEX - =1

Increase PWM duty cycle

Figure 3-2 Way to change PWM duty cycle

125

KHz

when . The overall cycle is still 12-bit to make the 12-bit



PWM

8fMHz

PWM

4096

MHz

0.512

. So Therefore, every change of the duty cycle will

Start

PWMEX>=

11111100B?

PWMEX + = 1

End

PWMEX = 0

PWMDATA + =1

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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

()



fd s

efficiency

Based on the above formulas, Table 1 shows the values of Ips, Imcu, Vfd, Vs, and efficiency (%).



(I)



ps MCU ps

and

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S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 4 SYSTEM VALIDATION

Table 4-1 System validation of efficiency

Ips (power supply) (mA) 300 288 306 285 300 288 309 290 308 304 Imcu (m A)

(MCU供电LED) Vfd V） Vs mV） Efficiency（%）

NOTE: BD1 and BD2 represent two boards, where the basic difference lies in the value of sensing resistance,

(1)1.0

RBD (2)1.1

； . Due to the same reason, the efficiency of BD2 is always better than that

of BD1. The nominal tolerance of VISHAY WSR2 is 1%.

RBD 

#1 #2 #3 #4 #5

BD1 BD2 BD1 BD2 BD1 BD2 BD1 BD2 BD1 BD2

18 19 18 19 18 19 18 19 18 19

3.82 3.6 357

87.68 81.6

340 359 340 351 340 359 341 358 360

3.85 3.60 3.86 3.6 3.90 3.59 3.90 3.65

87.03 82.5 87.35 81.6 87.37 80.95 87.45 81.11

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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 C1 104 C2 47uF Tantalum Capacitor C3 2nF

VISHAY

WSR21R000FEA

C4 100uF R4 33K ohms Q1 HEXFET Power MOSFET D1 Schottky Diode IN5819 L1 100 uH inductance HPLED 1W1 HPLED

5.2 APPENDIX 2: SOURCE CODE

For more information, refer to Source_Code_LED_S3F84P4_V10.

IR

TDK HangKe

IRF9540

VLF12060-101M1R0

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Samsung S3F84A5 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

APPLICATION NOTE

Important Notice

Revision History

Table of Contents

List of Figures

List of Tables

S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 1 OVERVIEW OF HPLED LIGHTING CONTROL SYSTEM

1.1 PIN ASSIGNMENT IN S3F84P4

1.2 KEY FEATURES OF S3F84P4

1.3 SYSTEM PRINCIPLE

1.3.1 BUCK CIRCUIT

1.3.2 SUMMARY

1.3.3 CONSTANT CURRENT CONTROL

2 HARDWARE IMPLEMENTATION

2.1 SYSTEM DIAGRAM AND CIRCUIT

2.2 COMPONENTS SELECTION

3 SOFTWARE IMPLEMENTATION

4 SYSTEM VALIDATION

5 APPENDIX

5.1 BOM LIST OF KEY CIRCUIT

5.2 APPENDIX 2: SOURCE CODE