Body Power / H. Hopfgartner LED Driving Concepts and Infineon® Basic LED Drivers A pplication Note V1.1 2011-06-29 A utomotive Power LED Driving Concepts and Infineon® Basic LED Drivers Basic LED Driver Revision History: V1.1, 2011-06-29 Previous Version: V1.0 Page Subjects (major changes since last revision) 9 BCR42xP removed Application Note 2 V1.1, 2011-06-29 LED Driving Concepts and Infineon® Basic LED Drivers Table of Contents Table of Contents 1 Abstract ............................................................................................................................................... 4 2 Introduction ........................................................................................................................................ 4 3 How to Control LEDs ......................................................................................................................... 4 4 Infineon® Basic LED Driver .............................................................................................................. 9 5 Conclusion ........................................................................................................................................ 17 6 Additional Information ..................................................................................................................... 17 Application Note 3 V1.1, 2011-06-29 LED Driving Concepts and Infineon® Basic LED Drivers Abstract 1 Abstract Note: The following information is given as a hint for the implementation of the device only and shall not be regarded as a description or warranty of a certain functionality, condition or quality of the device. Note: All application diagrams shown in this application note are very simplified examples of application circuits. The function must be verified in the real application. This application note is intended to provide detailed application hints regarding the usage and design in of the Infineon® Basic LED Drivers. The selection of external components is shown within this application note. Furthermore, different principles of LED driving concepts are explained. 2 Introduction The Infineon® Basic LED Drivers is a family of single- and three-channel current sources. The typical output current range is from 20 mA up to 2500 mA, which can be adjusted in most cases. Furthermore, some device also offer diagnosis features. This document shows how to define the external circuitry for the required output current and gives hints for diagnosis function. 3 How to Control LEDs Light emitting diodes (LED) are semiconductor pn-junctions. When the LED is forward biased, electrons are able to recombine with holes within the device, releasing energy in the form of photons. The LED’s forward current, which has to be limited, defines the brightness of the LED. The current limiting and setting can be done with different methods: • A resistor to limit the forward current • A linear current source to set a defined and stable current • A DCDC converter in constant current mode In automotive applications LED-modules for exterior lighting are usually controlled via a switch on the central body control module (BCM) as it is shown in Figure 1, Figure 2 and Figure 3. The reason is to protect the wire from the BCM to the LED-module against short circuits. The LED-control ICs are mounted very close to the LEDs to ensure: • A protection of the LEDs, if the wire from the BCM to the LED-module is shorted to the supply voltage • To react on high temperature conditions in the LED-module (active current reduction to protect LEDs) The following three chapters explain the different methods of LED control. Benefits and disadvantages are identified. Application Note 4 V1.1, 2011-06-29 LED Driving Concepts and Infineon® Basic LED Drivers How to Control LEDs 3.1 Resistor for LED Current Limitation A resistor can act only as a current limiter, but not as a current control circuit for the LED. The picture below shows the simplified circuit schematic with a resistor solution: Protected HS Switch (PROFET, SPOC, SPI LED) Series Resistor Switched VBATs (KL58d, KL30d …) VBAT (KL30) RLED PWM Body Control Module Figure 1 LED Module LED driving schematic The resistor has to be defined for the worst case supply voltage e.g. VBATs(max) = 18 V. E.g. An LED for a typical rear light application is operated usually at a typical current of ILED = 50 mA with a typical forward voltage of VF = 2.2V Therefore, the resistor RLED can be calculated for the example above (3 LEDs Æ n = 3): RLED = (1) VBATs (max) − n ⋅VF I LED = 18V − 3 ⋅ 2.2V = 228Ω 50mA The resistor RLED has to withstand a power loss of: PRLED = (VBATs (max) − n ⋅VF )⋅ I LED = (18V − 3 ⋅ 2.2V ) ⋅ 50mA = 0.6W (2) So, a power resistor is required. In case of lower supply voltages or voltage drops (e.g. start stop) the LED current is reduced, which leads to significant reduced brightness! If the supply voltage drops down to e.g. VBATs(min) = 9 V: I LED = (3) V BATs (min) − n ⋅ V F R LED = 9V − 3 ⋅ 2.2V = 11mA 228Ω Pros • Simplest solution Cons • High power loss across the RLED • Resistor needs to be defined for maximum supply voltage conditions. For typical supply voltage conditions the LED current is much lower, which leads to a visible decrease of brightness e.g. during start stop operation • LED nominal current range cannot be used for nominal operation conditions, because current has to be fixed for maximum supply voltage • No intrinsic overvoltage protection (during supply voltage spikes the LEDs are stressed significantly, because of exceeding the LEDs maximum ratings) Æ degradation of LEDs Application Note 5 V1.1, 2011-06-29 LED Driving Concepts and Infineon® Basic LED Drivers How to Control LEDs • No simple temperature protection of the LEDs possible Æ degradation of LEDs • Reduced LED lifetimeAny diagnosis functions needs to be realized by additional circuits • Only limited LED chain length, dependent on the LED forward voltage VF and minimum supply voltage 3.2 Linear Current Source for Constant Current Supply of LEDs A linear current source provides a constant output current to the LED over the entire supply voltage range. In addition to the benefits of the constant LED current diagnosis functions are provided by most linear current sources. The figure below shows a simplified LED module using a constant current source. Protected HS Switch (PROFET, SPOC, SPI LED) Linear Current Source (e.g. TLDxxx, BCR4xx) Switched VBATs (KL58d, KL30d …) VBAT (KL30) I = constant PWM Body Control Module Figure 2 LED Module LED driving schematic The LED current is controlled by the linear current source. The output current is constant and nearly fully independent of the VBATs. The LED current can be adjusted very easily by using external resistors. Details about current control and diagnosis are explained later in this application note. Pros • LED can be used in the nominal operation condition Æ full brightness • Stable brightness even during start stop • Intrinsic overvoltage protection • No LED degradation • High temperature protection of LEDs possible • Integrated diagnosis functions (optional) Cons • High power loss across the constant current source • Increased components count • Only limited LED chain length, dependent on the LED forward voltage VF and minimum supply voltage To increase the efficiency of the total system a so called Matrix setup could be used as described later in this application note. Application Note 6 V1.1, 2011-06-29 LED Driving Concepts and Infineon® Basic LED Drivers How to Control LEDs 3.3 DC/DC Converter in Constant Current Mode A DC/DC converter in constant current mode provides a constant output current to the LED over the entire supply voltage range. The power loss inside the LED control circuit is reduced to a minimum, because the configuration is optimized to the LED chain length. Furthermore, diagnosis functions are provided by most DC/DC converters. The figure below shows a simplified LED module using a DC/DC converter. Switched VBATs (KL58d, KL30d …) VBAT (KL30) DC/DC Buck or Boost in Constant Current Mode (e.g. TLD5085/45, TLD5095/8) Optional PWM BCM Control Parallel, LIN or CAN Control RSENSE Body Control Module Figure 3 LED Module LED driving schematic The LED current is controlled by the DC/DC converter. Different topologies (Buck, Boost, SEPIC, …) can be used to fulfill requirements regarding LED chain length and supply voltage range. The output current is constant and nearly fully independent of the VBATs. The LED current can be adjusted very easily by using external resistors. Pros • Highest efficiency • LED can be used in the nominal operation condition Æ full brightness • Stable brightness even during start stop • High brightness LEDs capable • Various topologies possible • Intrinsic overvoltage protection • No LED degradation • High temperature protection of LEDs possible • Integrated diagnosis functions (optional) Cons • Increased components count • PCB layout needs to be optimized regarding EMC performance Application Note 7 V1.1, 2011-06-29 LED Driving Concepts and Infineon® Basic LED Drivers How to Control LEDs 3.4 DC/DC Converter combined with Constant Current Source – Matrix Setup A DC/DC converter in constant voltage mode is combined with one or more linear current sources. The DC/DC converter provides an output voltage, which is optimized for the required LED chain length. The DC/DC’s output voltage is converted into a constant output current by the linear current sources. This system allows a more efficient LED controlled compared to a pure linear current source solution as described before. The figure below shows a simplified LED module using the Matrix setup. DC/DC Buck or Boost in Constant Voltage Mode (e.g. TLD5085/45, TLD5095/8) Switched VBATs (KL58d, KL30d …) VBAT (KL30) Linear Current Source (e.g. TLDxxx, BCR4xx) Optional PWM BCM Control Parallel, LIN or CAN Control Body Control Module Figure 4 LED Module LED driving schematic The LED current is controlled by the linear current source. The DC/DC converter output voltage is adjusted to the LEDs forward voltage. Different topologies (Buck, Boost, SEPIC, …) can be used to fulfill requirements regarding LED chain length and supply voltage range. The output current is constant and nearly fully independent of the VBATs. The LED current can be adjusted very easily by using external resistors. Pros • One DC/DC converter for multiple linear current sources • Current source supply, which is the DC/DC output, optimized to LED forward voltage • LED can be used in the nominal operation condition Æ full brightness • Stable brightness even during start stop • Various topologies possible • Higher efficiency than pure linear current source solution • Intrinsic overvoltage protection • No LED degradation • High temperature protection of LEDs possible • Integrated diagnosis functions (optional) Cons • Increased components count • PCB layout needs to be optimized regarding EMC performance Application Note 8 V1.1, 2011-06-29 LED Driving Concepts and Infineon® Basic LED Drivers Infineon® Basic LED Driver 4 Infineon® Basic LED Driver Infineon provides numerous automotive qualified constant current source products for optimized LED control within automotive interior and exterior lighting applications. In the following explanation an overview of all current available products is given. Table 1 Infineon® Basic LED Driver Overview Current mA adj. Open Load Detection PWM/Ena ble Hi/Low Current Switch Package BCR40xU 10-50typ SC-74 BCR420U 150typ SC-74 BCR421U 150typ SC-74 TLD1211SJ 85typ DSO-8 TLE4240-2M 60typ SCT-595 TLE4240-3M 60typ SCT-595 TLE4241GM 70max DSO-8 TLE4242G 450typ TO-263 TLD1211SJ + ext NPN <2500 DSO-8 4.1 BCR4xx Family - Low Cost Linear Current Sources The BCR4xx family includes low cost constant current source LED drivers offering current adjustment features without diagnostic functions for easiest design in. Table 2 BCR4xx Product and Feature Overview Topology Input voltage min [V] Input voltage max [V] Output current [mA] PG-SC74-6 Linear 4.5 40 150 BRC421U PG-SC74-6 Linear 4.5 40 150 BCR401U PG-SC74-6 Linear 4.5 40 10 BCR402U PG-SC74-6 Linear 4.5 40 20 BCR405U PG-SC74-6 Linear 4.5 40 50 Product type Package BCR420U Application Note 9 Inhibit PWM Open load detection V1.1, 2011-06-29 LED Driving Concepts and Infineon® Basic LED Drivers Infineon® Basic LED Driver Key Features: • Low cost technology & package • Output current adjustable by usage of external resistor, without external resistor output current is fixed to specified value • Suitable for Pulse Width Modulation (PWM) • Negative temperature coefficient (LED protection @ high temperatures) • Available in several package options: SOT143R, SOT343, SC74 • Possibility to operate as control circuit with an external NPN-power transistor as output stage • Automotive Qualified 4.1.1 Integrated Output Stage Usage Figure 5 Schematic The LED current can be adjusted by using the external resistor REXT. If no external resistor is mounted, the LED current is fixed to the specified value according to the data sheet. With equipped REXT the output current is defined by the following equation. The values used for the example are based on the BCR401: (4) I OUT = Vdrop ** * Rint ⋅ REXT ** Rint + REXT ≈ 0.91V 91Ω ⋅ REXT 91Ω + REXT With: * Vdrop according to data sheet graph “reference voltage (Vdrop) versus IOUT”, typ. 0.91V ** Rint according to data sheet parameter Rint, typ. 91Ω Application Note 10 V1.1, 2011-06-29 LED Driving Concepts and Infineon® Basic LED Drivers Infineon® Basic LED Driver 4.1.2 External Output Stage Usage The devices of the BCR4xx family can be used also as control IC for an external NPN-transistor as output stage for high LED currents according to the following schematic. The basic LED driver is driving only a very small current, which is the base current for the external NPN transistor. Therefore, in a lot of cases the BCR401 devices are sufficient. Vbat BCR402U Controller BCR401Rasas Controller Vs Rsense Rext LEDs GND Iout R1 R2 Figure 6 NPN Power Transistor e.g. BCX55-16 Schematic The resistors Rsense, R1 and R2 can be calculated according to the following equations. All parameters marked with a star * are related to the transistor’s data sheet. I LED = Vdrop Rint ⋅ Rsense Rint + Rsense The transistor base current is defined by: (6) IB = I LED B* B...DC current gain of transistor The resistor R2 is calculated according: (7) R2 = VBE ( on ) I R2 * I R 2 = 2...10 ⋅ I B The resistor R1 is calculated according: (8) R1 = V BAT (min) − VS (min) − V BE ( on ) Application Note * I B + I R2 11 V1.1, 2011-06-29 LED Driving Concepts and Infineon® Basic LED Drivers Infineon® Basic LED Driver 4.2 TLD1211SJ - Linear LED Driver The TDL1211SJ is a linear current source providing currents up to 85mA and having an integrated high temperature current reduction feature to protect the connected LEDs against to high temperatures. Furthermore, it supports the current control function of an external NPN transistor. Key Features: • Max. Output current 85mA • Temperature dependent current reduction • External Transistor Option LED currents up to 2.5A • Improved precision of output current: +/- 10% in whole operating range (Vsupply; Tj) • Over voltage protection • Enable input for PWM operation • DSO-8 package • Automotive Qualified 4.2.1 Integrated Output Stage Usage Rsense Figure 7 Schematic Application Note 12 V1.1, 2011-06-29 LED Driving Concepts and Infineon® Basic LED Drivers Infineon® Basic LED Driver The LED current can be adjusted by the sense resistor Rsense: * (9) I OUT = Vsense Rsense With Vsense according to datasheet parameter 4.3.9, typ. 150mV 4.2.2 External Output Stage Usage The TLD1211SJ can be used also as control IC for an external NPN-transistor as output stage for high LED currents according to the following schematic. The basic LED driver is driving only a very small current, which is the base current for the external NPN transistor. VBAT BAS3010A-03W 5V VQ VI 10µF VREG TLE4264 µC OUT/ PWM GND GND 1,8kΩ 1kΩ 47nF R1 = 820Ω BCX55-16 R2 = 100Ω Figure 8 Rsense = 0,42Ω Schematic The resistors Rsense, R1 and R2 can be calculated according to the following equations. All parameters marked with a star * are related to the transistor’s data sheet. I B (11) Rsense = = I LED B* B...DC current gain of transistor Vsense with I sense = I Load + I B I sense The resistor R2 is calculated according: Application Note 13 V1.1, 2011-06-29 LED Driving Concepts and Infineon® Basic LED Drivers Infineon® Basic LED Driver (12) I R 2 = n ⋅ I B with n = 2...10 * V + Vsense (13) R2 = BE with I sense = I Load + I B I R2 The resistor R1 is calculated according: * V − VBE − Vsense ** with VOUT = VS − Vdrop (14) R1 = OUT I B + I R2 ** Vdrop is the datasheet parameter 4.3.11 (Vs-Vout), max. 1.3V 4.3 TLE4240-2/-3M - Linear LED Driver The TLE4240-2/-3M is a linear current source with a fixed output current of typically 60mA. The TLE4240-3M offers an open load diagnosis. Key Features: • Constant Output Current of typ. 60 mA • Low dropout voltage • Open Load Diagnosis Output (Version TLE4240-3 only) • Safe Operation Area circuit monitoring drop voltage • Short Circuit Protection to GND and VBAT (up to 45V) • Reverse polarity protected • Package SCT-595 • Automotive Qualified Figure 9 Schematic The status pin ST is an open collector pin. In normal load condition ST-pin is high impendent Æ HIGH. In open load condition ST-pin is pulled to GND Æ LOW. Application Note 14 V1.1, 2011-06-29 LED Driving Concepts and Infineon® Basic LED Drivers Infineon® Basic LED Driver 4.4 TLE4241GM - Linear Dual Mode LED Driver The TLE4241GM is a dual mode linear current source with adjustable output current up to 70mA. By applying a low or high signal at the SET-pin the output current can be changed by a ratio of typ. 7. Key Features: • Adjustable Constant Output Current up to 70 mA • Low Dropout Voltage • Dual Mode for Tail and Stop Light (low/high current SET) • PWM Input (e. g. for individual dimming) up to 1kHz • Open Load Diagnosis Output • Input Voltage Range up to 45 V • Reverse Polarity Protected • Short Circuit Protection to GND and VBAT • Small SMD Package: P-DSO-8 • Operating range: -40…150 °C • Over-Temperature Protection • Automotive Qualified Figure 10 Schematic When the SET-pin is at low potential the output current is the low level. As soon as the SET-pin is switched to high potential (up to VBAT) the high output current is active. The output current can be adjusted additionally by the sense resistor RSENSE. If the SET-pin is connected to high potential (e.g. 5V) the high output current can be calculated: Application Note 15 V1.1, 2011-06-29 LED Driving Concepts and Infineon® Basic LED Drivers Infineon® Basic LED Driver (15) I Q ,typ ,SET = H = * Vref Rref ⋅ 487 + 0.1 If the SET-pin is connected to low potential (0V): Vref (16) I Q ,typ ,SET = L = * Rref ⋅ 487 + 0.1 I QH / I QL ** * According to data sheet diagram “Reference voltage versus junction temperature”, typ. 1.2V ** IQH/IQL is the data sheet parameter “current ratio”, typ. 7 4.5 TLE4242G - Linear 1 Watt LED Driver The TLE4242G is a linear current source for driving high brightness LEDs up to 1W. It provides a PWM input and a diagnosis output. Key Features: • Adjustable Output Current up to 500mA • Low dropout voltage • PWM Input (dimming, switching between brake and tail light, …) • Diagnosis Output • Over-Temperature Protection • Short Circuit Protection to GND and VBAT • Reverse Polarity Protected • Input Voltage Range up to 45 V • Package TO-263-7 • Automotive Qualified Application Note 16 V1.1, 2011-06-29 LED Driving Concepts and Infineon® Basic LED Drivers Conclusion Figure 11 Schematic The output current can be adjusted by the reference resistor RREF. If the SET-pin is connected to high potential (e.g. 5V) the high output current can be calculated: (17) I Q ,typ = Vref * Rref * According to data sheet diagram “Reference voltage versus junction temperature”, typ. 177mV The diagnosis response time can be adjusted by the capacitor connected to the diagnosis-pin D: (18) t STHL ,typ = 5 CD C ⋅ 10ms t STLH ,typ = D ⋅ 10µs 47nF 47nF Conclusion Infineon® Basic LED Drivers are able to drive small signal LEDs up to high brightness LEDs. The dimensioning of the required external components is supported by this application note. 6 • • • Additional Information For further technical details, please contact us. Existing App. Notes o AN101, Using Infineon‘s BCR400 Family of Constant-Current, Linear-Mode LED Drivers for Lighting Applications from 10 mA - 700 mA o AN97, Using BCR402R/BCR402U at High Supply Voltages For further information you may contact http://www.infineon.com/automotive-leddrivers Application Note 17 V1.1, 2011-06-29 Edition 2011-06-29 Published by Infineon Technologies AG 81726 Munich, Germany © 2011 Infineon Technologies AG All Rights Reserved. LEGAL DISCLAIMER THE INFORMATION GIVEN IN THIS APPLICATION NOTE IS GIVEN AS A HINT FOR THE IMPLEMENTATION OF THE INFINEON TECHNOLOGIES COMPONENT ONLY AND SHALL NOT BE REGARDED AS ANY DESCRIPTION OR WARRANTY OF A CERTAIN FUNCTIONALITY, CONDITION OR QUALITY OF THE INFINEON TECHNOLOGIES COMPONENT. THE RECIPIENT OF THIS APPLICATION NOTE MUST VERIFY ANY FUNCTION DESCRIBED HEREIN IN THE REAL APPLICATION. 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Life support devices or systems are intended to be implanted in the human body or to support and/or maintain and sustain and/or protect human life. If they fail, it is reasonable to assume that the health of the user or other persons may be endangered. w w w . i n f i n e o n . c o m Published by Infineon Technologies AG