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Freescale Semiconductor S08 manual Current Sense Resistor, Boost Converter

Models: S08

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2.11.2 Current Sense Resistor

Hardware Description

2.11.2 Current Sense Resistor

The value of the current sense resistor RS is determined by two factors: power dissipation on RS and the reference level VREF for operational amplifier non-inverting input. Smaller RS reduces power dissipation, but the detection of a feedback signal in operational amplifier is more difficult.

The voltage VRS across the current sense resistor RS is directly proportional to the current ILED through LED. In closed-loop condition, VRS is equal to the reference level VREF, so the LED current ILED is equal to the reference voltage VREF divided by the current sense resistor RS.

Setting VREF to 1V and RS equals 20Ω, the LED current ILED is equal to 50mA.

Power dissipation on RS is around 50mW, I2R = (50mA)2 × 20Ω, which is reasonable compared to total LED power.

2.11.3 Boost Converter

The switching regulator MC34063 from On Semiconductor is a monolithic circuit containing the primary functions required for DC-to-DC converters. It can be incorporated in boost converter application with minimum number of external components.

Boost Converter Calculations:

Output voltage VOUT > (VLED x 8) + VRS + VDROP (set maximum linear drop to 2 V)

Output current Iout > 50 mA x 3

Set Vin = 12 V, Vout = 30 V, and Iout = 175 mA

Refer to equations in Figure 2-4to calculate the values for inductor and other external components.

LED Lighting Control using the MC9S08AW60, Rev. 1

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Freescale Semiconductor S08 manual Current Sense Resistor, Boost Converter

Contents

LED Lighting Control Using the MC9S08AW60 Designer Reference ManualS08 Microcontrollers freescale.comPage Designer Reference Manual LED Lighting Control using the MC9S08AW60Revision History Revision History LED Lighting Control using the MC9S08AW60, Rev Freescale SemiconductorTable of Contents Demo SetupChapter IntroductionAppendix A Schematics Appendix B Bill of Materials 1.1 Introduction 1.2 FeaturesChapter Introduction 1.3 System Overview 1.4 MC9S08AW60Figure 1-1 . System Block Diagram Table 1-1. Devices in the MC9S08AW60/48/32/16 SeriesFeature LED Lighting Control using the MC9S08AW60, RevTable 1-2. Peripherals Available per Package Type MC9S08AW60Introduction LED Lighting Control using the MC9S08AW60, Rev Freescale SemiconductorChapter Hardware Description 2.1 IntroductionAW60 Control Board Figure 2-1. Light-Box DemoFigure 2-2. DEMO9S08AW60LED Top Side 2.2 DEMO9S08AW60LED Features2.3 DEMO9S08AW60LED Layout 2.5 Power 2.6 Reset Switch2.4 Development Support 2.7 Clock Source2.9.1 Pushbutton Switches 2.9.2 LED Indicators2.9 User Options 2.9.3 ADC Interface2.9.4 Other I/O Connectors Table 2-5. IIC PortTable 2-6. SCI Port Table 2-7. SPI PortTable 2-10. Sensor Interface Type A Table 2-8. PWM PortTable 2-9. LED Light Box Interface Table 2-13. User Assignable Input Table 2-12. Temperature Sensor InputTable 2-11. Sensor Interface Type H 2.10 LED Driving Board Table 2-13. User Assignable Input ContinuedFigure 2-3. DC-to-DC Boost Converter and Linear LED Driver 2.11 LED Driver Design Procedures2.11.1 RGB LED Chip 2.11.2 Current Sense Resistor 2.11.3 Boost ConverterFigure 2-4. Equations for Boost Converter Hardware Description LED Lighting Control using the MC9S08AW60, Rev Freescale SemiconductorFigure 3-1. Firmware Flow Main Program Chapter Firmware Description3.1 Introduction 3.2 PC Control Mode Figure 3-2. Firmware Flow PWM AdjustmentFigure 3-3. User Interface Menu 3.3 Standalone Mode 3.4 Firmware Files Main.cMenu.c SCI.cFirmware Description LED Lighting Control using the MC9S08AW60, Rev Freescale SemiconductorChapter Demo Setup 4.2 Hardware and Software Setup4.2.1 Hardware Setup 4.2.2 PC Software SetupLED Lighting Control using the MC9S08AW60, Rev Figure 4-1. Echo Typed Characters SettingDemo Setup Figure 4-2. LED Control Menu 4.3 Demo Examples4.3.1 Demo 1 - Demonstration Display 4.3.2 Demo 2 - Preset Colors Display 4.3.3 Demo 3 - Auto White Balance Control4.3.4 Demo 4 - PWM Output Frequency Control 4.3.5 Demo 5 - Full Manual Control4.5 Troubleshooting 4.4 Program the MCU FlashRepeat the PC software setup procedures again Appendix A Schematics LED Lighting Control using the MC9S08AW60, RevLED Lighting Control using the MC9S08AW60, Rev Freescale SemiconductorLED Lighting Control using the MC9S08AW60, Rev Freescale SemiconductorLED Lighting Control using the MC9S08AW60, Rev Freescale SemiconductorLED Lighting Control using the MC9S08AW60, Rev Freescale SemiconductorLED Lighting Control using the MC9S08AW60, Rev Freescale SemiconductorAppendix B Bill of Materials LED Lighting Control using the MC9S08AW60, RevLED Lighting Control using the MC9S08AW60, Rev Table 4-1 BOM for AW60 Control BoardPart Description QuantityTable 4-2 BOM for LED Driving Board Part DescriptionValue DesignatorsLED Lighting Control using the MC9S08AW60, Rev Freescale SemiconductorPage How to Reach Us Home PageE-mail USA/Europe or Locations Not Listed