User’s Guide September 2002 PMP EVMs SLLU053 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All products are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment. TI warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with TI’s standard warranty. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. Except where mandated by government requirements, testing of all parameters of each product is not necessarily performed. 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Mailing Address: Texas Instruments Post Office Box 655303 Dallas, Texas 75265 Copyright 2002, Texas Instruments Incorporated EVM IMPORTANT NOTICE Texas Instruments (TI) provides the enclosed product(s) under the following conditions: This evaluation kit being sold by TI is intended for use for ENGINEERING DEVELOPMENT OR EVALUATION PURPOSES ONLY and is not considered by TI to be fit for commercial use. As such, the goods being provided may not be complete in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including product safety measures typically found in the end product incorporating the goods. As a prototype, this product does not fall within the scope of the European Union directive on electromagnetic compatibility and therefore may not meet the technical requirements of the directive. Should this evaluation kit not meet the specifications indicated in the EVM User’s Guide, the kit may be returned within 30 days from the date of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY SELLER TO BUYER AND IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE. The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user indemnifies TI from all claims arising from the handling or use of the goods. Please be aware that the products received may not be regulatory compliant or agency certified (FCC, UL, CE, etc.). Due to the open construction of the product, it is the user’s responsibility to take any and all appropriate precautions with regard to electrostatic discharge. EXCEPT TO THE EXTENT OF THE INDEMNITY SET FORTH ABOVE, NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES. TI currently deals with a variety of customers for products, and therefore our arrangement with the user is not exclusive. TI assumes no liability for applications assistance, customer product design, software performance, or infringement of patents or services described herein. Please read the EVM User’s Guide and, specifically, the EVM Warnings and Restrictions notice in the EVM User’s Guide prior to handling the product. This notice contains important safety information about temperatures and voltages. For further safety concerns, please contact the TI application engineer. Persons handling the product must have electronics training and observe good laboratory practice standards. No license is granted under any patent right or other intellectual property right of TI covering or relating to any machine, process, or combination in which such TI products or services might be or are used. Mailing Address: Texas Instruments Post Office Box 655303 Dallas, Texas 75265 Copyright 2002, Texas Instruments Incorporated EVM WARNINGS AND RESTRICTIONS It is important to operate this EVM within the input voltage range of 1.8 V to 6.0 V. Exceeding the specified input range may cause unexpected operation and/or irreversible damage to the EVM. If there are questions concerning the input range, please contact a TI field representative prior to connecting the input power. Applying loads outside of the specified output range may result in unintended operation and/or possible permanent damage to the EVM. Please consult the EVM User’s Guide prior to connecting any load to the EVM output. If there is uncertainty as to the load specification, please contact a TI field representative. During normal operation, some circuit components may have case temperatures greater than 60°C. The EVM is designed to operate properly with certain components above 60°C as long as the input and output ranges are maintained. These components include but are not limited to linear regulators, switching transistors, pass transistors, and current sense resistors. These types of devices can be identified using the EVM schematic located in the EVM User’s Guide. When placing measurement probes near these devices during operation, please be aware that these devices may be very warm to the touch. Mailing Address: Texas Instruments Post Office Box 655303 Dallas, Texas 75265 Copyright 2002, Texas Instruments Incorporated Related Documentation From Texas Instruments Preface About This Manual This user’s guide describes the characteristics, operation, and use of the TPS61042EVM–226 white light LED bias supply evaluation module (EVM). This EVM is a Texas Instruments high-efficiency boost converter that is configured to supply 20 mA of bias current to four white light LEDs, from a 1.8 V to 6 V input voltage. The user’s guide includes a schematic diagram and bill of materials (BOM). How to Use This Manual This document contains the following chapters: - Chapter 1 – Introduction - Chapter 2 – Setup - Chapter 3 – Board Layout - Chapter 4 – Schematic and Bill of Materials Related Documentation From Texas Instruments TPS61042 data sheet (SLVS439) If You Need Assistance. . . Contact your local TI sales representative. FCC Warning This equipment is intended for use in a laboratory test environment only. It generates, uses, and can radiate radio frequency energy and has not been tested for compliance with the limits of computing devices pursuant to subpart J of part 15 of FCC rules, which are designed to provide reasonable protection against radio frequency interference. Operation of this equipment in other environments may cause interference with radio communications, in which case the user at his own expense will be required to take whatever measures may be required to correct this interference. v vi Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 2 Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Input/Output Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 EVM Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1 Analog Dimming With Analog Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.2 Analog Dimming With PWM Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.3 PWM Dimming Using CTRL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Board Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 3.1 Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2 4 Schematic and Bill of Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1 4.1 Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2 4.2 Bill of Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3 2-1 2-2 2-2 2-2 2-3 2-4 2-4 3–1 3–2 3–3 Assembly Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2 Top Layer Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2 Bottom Layer Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3 2–1 4–1 Input/Output Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2 TPS61042EVM-226 Bill of Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3 vii Contents viii Chapter 1 This chapter contains background information for the TPS61042 and support documentation for the TPS61042EVM–226 evaluation module. Topic 1.1 Page Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 Introduction 1-1 Background 1.1 Background This TPS61042EVM uses the TPS61042 boost converter to provide 20 mA of bias current to a four-element white LED from a 1.8 V to 6 V input. This EVM may be modified to drive more or less than four LEDs. It may also be modified to deliver a higher or lower output current to the LEDs. Refer to the data sheet for more information on adjusting the rated output current. The EVM includes a CTRL pin and an ADJ pin that allows the user to dim the LEDs. The LEDs may be dimmed using either an analog or a PWM dimming scheme. Information about output voltage and current ratings of TPS61042 can be found in the data sheet SLVS439. 1-2 Chapter 2 This chapter describes how to properly connect, set up, and use the TPS61042EVM-226. Topic Page 2.1 Input/Output Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2 2.2 EVM Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2 2.3 Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4 Setup 2-1 Input/Output Connections 2.1 Input/Output Connections The TPS61042EVM–226 PWB has several connections, which are described in Table 2–1. Table 2–1. Input/Output Connections Reference Designator Name Description J1 Vin This is the positive connection to the input power supply. The leads to the input supply should be twisted and kept as short as possible. J2 GND This is the return connection for the input power supply J3 ADJ Input for dimming adjust of LED current J4–1 ON Connect J4–2 (CTRL) to J4–1 (ON) with a shorting jumper to enable the supply J4–2 CTRL CTRL J4–3 OFF Connect J4–2 (CTRL) to J4–3 (OFF) with a shorting jumper to disable the supply 2.2 EVM Operation The EVM is configured as a constant current supply. Current regulation is accomplished by regulating the voltage across a current sense resistor. The EVM does not operate correctly unless a load is present. The EVM is shipped with four white light LEDs as a load. If these are removed, they must be replaced with another load that falls within the voltage and current limit specs of the device. The TPS61042 has built-in overvoltage protection to keep the EVM from being damaged under a no-load condition. This EVM is designed to accommodate several LED-dimming techniques. Because of this flexibility, circuitry may be present on the EVM that is not needed for the particular dimming method that the user chooses. Depending on the PWM dimming technique used, component values may need to be changed to provide the desired LED current level. The first step to be completed before the EVM is used is to determine the method of dimming. Several dimming techniques are described below. 2.2.1 Analog Dimming With Analog Voltage One method for dimming the LEDs is to inject a voltage through a resistor into the FB pin of the TPS61042. The injected voltage artificially raises the voltage seen at the FB pin, which lowers the LED current. If the resistor values are chosen correctly, the analog control voltage varies the output current from 0mA to full LED current. This dimming method is accomplished by injecting an analog voltage into the ADJ pin on J3. The equations below calculate the required resistor values where: - Vref is the TPS61042 reference voltage = 0.250 V - Vadj_min is the minimum adjust voltage - Vadj_max is the maximum adjust voltage 2-2 EVM Operation - Io_min is the minimum output current - Io_max is the maximum output current - Reference designators correspond to the EVM schematic shown in Chapter 4 R2 + V V R1 + ref ǒIo_max R3 * Io_min R3 ) Vadj_min * Vadj_maxǓ ǒVref * Vadj_minǓ ) Io_max ǒVadj_max * VrefǓ I o_min R3 ) V ref I o_min R2 * V R2 adj_max ref R3 * V ) V adj_max ref If Vref = 0.25 V, Vadj_min = 0 V, Vadj_max = 3.3 V, Io_min = 0 A, Io_max = 20 mA, and R3 = 121 kΩ, R2 is calculated to be 9.9 kΩ, and R1 is calculated to be 13.5 Ω. 2.2.2 Analog Dimming With PWM Voltage The second method for dimming the LEDs is to inject a pulse width modulated (PWM) voltage for analog dimming. With this method, an RC filter is used to convert the PWM control voltage into an analog voltage. The component values of the RC filter depend upon the frequency of the PWM voltage and the amount of allowable ripple on the converted analog signal. The converted analog voltage is then injected into the FB pin of the TPS61042 as in the Analog Dimming with Analog Voltage method described above. The output current decreases as the duty cycle increases. 0% duty cycle delivers maximum LED current and 100% duty cycle delivers minimum LED current. For this dimming method the PWM signal must be filtered and converted to its analog equivalent before it is applied to the EVM. The filtered signal is then applied to J3. Assuming that the PWM control voltage amplitude varies between 0 V and 3.3 V, the resistor values calculated in the Analog Dimming with Analog Voltage method may still be used. The following equation converts the PWM control voltage into its equivalent analog control voltage where: - Vpwm_pk is the peak to peak voltage of the injected PWM signal - D is the duty cycle of the injected PWM signal - Vmin is the minimum voltage of the injected PWM signal Vanalog = Vpwm_pk × D + Vmin Setup 2-3 Setup 2.2.3 PWM Dimming Using CTRL The third method for dimming the LEDs is to inject a PWM voltage into the CTRL pin of the TPS61042. The LED current is proportional to the CRTL pin duty cycle. Refer to the TPS61042 data sheet for more information on this dimming method. For this dimming method, R2 and R3 are not needed. R2 may be shorted and R3 may be removed if desired. R1 is calculated by the following equation where Vref is the reference voltage of the TPS61042 (0.25 V) and Iout_max is the maximum desired output current. The reference designators correspond to the EVM schematic shown in Chapter 4. R1 + V ref I o_max For an output current of 20 mA, R1 = 12.5 Ω. 2.3 Setup After the EVM has been modified for the appropriate dimming method, connect an input supply between J1 and J2. The EVM operates with an input voltage between 1.8 V and 6.0 V. The user must ensure that the input voltage never exceeds the part’s absolute maximum input voltage rating of 7.0 V. To enable the supply, move the jumper on J4 so that the CTRL pin is connected to the ON pin. The EVM comes preloaded with four white light LEDs; therefore, no external load is required for the EVM to operate properly. 2-4 Chapter 3 This chapter provides the TPS61042EVM-226 board layout and illustrations. Topic 3.1 Page Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2 Board Layout 3-1 Layout 3.1 Layout Board layout is critical for all switch mode power supplies. Figures 3–1, 3–2, and 3–3 show the board layout for the TPS61042EVM–226 PWB. The nodes with a high switching frequency are short and are isolated from the noise sensitive feedback circuitry. Careful attention has been given to the routing of high frequency current loops. Refer to the data sheet for specific layout guidelines. Figure 3–1. Assembly Layer Figure 3–2. Top Layer Routing 3-2 Layout Figure 3–3. Bottom Layer Routing Board Layout 3-3 3-4 Chapter 4 This chapter provides the TPS61042EVM–226 schematic and bill of materials. Topic Page 4.1 Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2 4.2 Bill of Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3 Schematic and Bill of Materials 4-1 Schematic 4.1 Schematic 4-2 Bill of Materials 4.2 Bill of Materials Table 4–1. TPS61042EVM-226 Bill of Materials Count Ref Des Description Size MFR Part Number 1 C1 Capacitor, ceramic, 4.7 µF, 6.3 V, X5R, 10% 805 Murata GRM21BR60J475KA11 1 C2 Capacitor, ceramic, 0.1 µF, 25 V, X7R, 10% 603 Murata GRM188R71E104KA01 1 D1 Diode, Schottky, 400 mA, 40 V SOD323 Zetex ZHCS400 4 D2, D3, D4, D5 Diode, LED, white, 30 mA 1210 Lumex SML–LX2832UWC–TR 3 J1, J2, J3 Header, 2-pin, 100 mil spacing, (36-pin strip) 0.100 x 2 Sullins PTC36SAAN 1 J4 Header, 3-pin, 100 mil spacing, (36-pin strip) 0.100 x 3 Sullins PTC36SAAN 1 L1 Inductor, 4.7 µH, 750 mA, 216 mΩ 0.500 x 0.500 Sumida CMD4D11–4R7 1 R1 Resistor, chip, 13.7 Ω, 1/16-W, 1% 603 Std Std 1 R2 Resistor, chip, 10 kΩ, 1/16-W, 1% 603 Std Std 1 R3 Resistor, chip, 121 kΩ, 1/16-W, 1% 603 Std Std 1 U1 IC, LED driver QFN–8P TI TPS61042QFN 1 –– PCB, 1.2 In x 1.05 In x .062 In Any SLVP226 1 –– Shunt, 100 mil, black 3M 929950–00 0.100 Schematic and Bill of Materials 4-3 4-4