User’s Guide September 2004 PMP EVMs SLVU068A
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.
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.
EVM WARNINGS AND RESTRICTIONS It is important to operate this EVM within the specified input and output ranges described in the EVM User’s Guide. This EVM is designed to operate over an input range of 1.8 V to 6 V and over a load range of 0.1 mA to 20 mA. 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.
Related Documentation From Texas Instruments Preface About This Manual This user’s guide describes the characteristics, operation, and use of the TPS61040EVM−002 white light LED bias supply evaluation module (EVM). This EVM is a Texas Instruments high-efficiency boost converter configured to supply 20 mA of bias current to four white light LEDs, from a single-cell Li-ion battery. The user’s guide includes a schematic diagram, bill of materials (BOM), and test data.
This page intentionally left blank vi
Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 1.2 Performance Specification Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 2 Setup and Test Results . . . . . . . . . . . . . . . . . . .
Contents 2−1 2−2 2−3 2−4 2−5 2−6 2−7 2−8. 2−9 2−10 3−1 3−2 3−3 Start-up Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5 Output Ripple Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6 SW Waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 1 This chapter contains background information for the TPS61040 and support documentation for the TPS61040EVM-002 evaluation module. Topic Page 1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 1.2 Performance Specification Summary . . . . . . . . . . . . . . . . . . . . . . . . . . .
Background 1.1 Background The TPS61040EVM uses the TPS61040 boost converter to provide 20 mA of bias current to a four-element white LED from a single-cell Li-ion battery (3 V to 4.2 V). The EVM operates over an input voltage range of 1.8 V to 6.0 V, but has been optimized over a 3-V to 4.2-V input range. Operation with an input voltage down to 1.8 V is possible, depending on the number of LEDs and the desired bias current. The EVM can also be configured for higher or lower output currents.
Chapter 2 This chapter describes how to properly connect, set up, and use the TPS61040EVM−002. It also presents the test results for the EVM. All test results are measured with the EVM driving four white light LEDs. Topic Page 2.1 Input/Output Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2 2.2 EVM Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2 2.3 Setup . . . . . . . . . . . .
Input/Output Connections 2.1 Input/Output Connections The TPS61040EVM−002 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. Input supply leads (Vin and GND) should be a twisted pair and kept as short as possible. J2 GND This is the return connection for the input power supply.
EVM Operation 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 between 0 mA and maximum programmed current. This dimming method is the default configuration of the EVM, and is accomplished by injecting an analog voltage into the DIM1 pin on J3. When using this method, R1 and C2 do not affect the operation of the EVM. The EVM is designed so that an analog voltage of 0 V to 3.
Setup 2.2.3 PWM Dimming Using Enable The third method for dimming the LEDs is to inject a PWM voltage into the EN pin of the TPS61040. When the EN pin is high, the supply turns on and the output current is at the programmed maximum current. When the EN pin is low, the supply turns off and the output current goes to 0 mA. If the frequency of the PWM voltage is greater than 100 Hz, the human eye can not detect the on and off state of the LED current.
Start-up 2.4 Start-up When enabled, the EVM goes through its programmed three-stage soft-start sequence to reduce inrush current at turnon. Figure 2−1 shows the startup sequence of the EVM when powered from a 4.0-V Li-ion battery. The top oscilloscope trace is the input current and the bottom trace is the output current. Figure 2−1. Start-up Waveforms 3 0.5 ms 100 mA 4 0.5 ms 10 mA 1 2 3 4 0.5 ms 5 mV 0.2 V 0.
LED Ripple Current 2.5 LED Ripple Current Figure 2−2 shows the output ripple current with Iout = 20 mA. The top oscilloscope trace shows the ripple with 3.6-V input, and the bottom trace shows the ripple with a 4.2-V input. The difference in switching frequency between the two traces is expected and is explained in the data sheet. Figure 2−2. Output Ripple Current A :M1 2 µs 2 mA/div 1 2 µs 2 mA/div 1 2 3 4 2-6 2 µs 12.4 mV 0.2 V 0.
Switching Waveforms 2.6 Switching Waveforms Figure 2−3 shows the switching waveform at the SW pin of the TPS61040. When the internal FET turns on, the voltage at the SW pin is pulled to ground until the inductor current reaches 400 mA. When the inductor current reaches 400 mA, the FET turns off and the voltage at the SW pin rises to the output voltage plus the forward voltage drop of the diode. During this time, the inductor transfers its stored energy to the load and the output capacitor.
Efficiency 2.7 Efficiency Figure 2−4 shows the measured efficiency of the TPS61040. Figure 2−4. Typical Efficiency 90 89 VI = 6 V 88 VI = 4.2 V Efficiency % 87 VI = 3.6 V 86 85 84 83 VI = 2.5 V 82 81 80 2.5 5 7.5 10 12.5 15 IO − Output Current − mA 17.5 20 2.8 Analog Dimming With Analog Voltage Data The EVM was modified to generate a 0 mA to 20 mA output when the control voltage is varied from 3.3 V to 0 V.
Analog Dimming With PWM Voltage Data 2.9 Analog Dimming With PWM Voltage Data For the Analog Dimming With PWM Voltage method, the EVM is configured identically with the Analog Dimming With Analog Voltage method with the exception that the control voltage is injected into the DIM2 pin on J3. R1 and C2 are chosen to be 10 kΩ and 1 µF to adequately filter a 1-kHz control voltage.
PWM Dimming Using Enable Data 2.10 PWM Dimming Using Enable Data For the PWM Dimming Using Enable method, the EVM is configured with R2= open and R3 = short. Setting R4 = 61.9 Ω programs the maximum output current to 20 mA. Figure 2−7 shows input current and output current with the PWM frequency set to 100 Hz and 50% duty cycle. The top oscilloscope trace is the output current and the bottom trace is the control voltage seen on the EN pin. Note the three-stage soft start during the first 1.
PWM Dimming Using Enable Data Figure 2−8.
PWM Dimming Using Injected Voltage on FB Data 2.11 PWM Dimming Using Injected Voltage on FB Data For the PWM Dimming Using Injected Voltage on FB method, a 0-V to 3.3-V control voltage is used to program a maximum LED current of 20 mA. Use the equations found in the Analog Dimming Using Analog Voltage section to calculate the resistor values. The following component values are used: R2 = 249 kΩ, R3 = 147 kΩ, R4 = 100 Ω. R2 and C2 are unpopulated (left open) for this configuration.
PWM Dimming Using Injected Voltage on FB Data Figure 2−10.
This page intentionally left blank 2-14
Chapter 3 This chapter provides the TPS61040EVM-002 board layout and illustrations. Topic 3.1 Page Board Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Board Layout 3.1 Board 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 TPS61040EVM−002 PWB. The nodes with a high switching frequency are short and are isolated from the noise-sensitive feedback circuitry. Careful attention is given to the routing of high-frequency current loops. See the data sheet for specific layout guidelines. Figure 3−1. Assembly Layer Figure 3−2.
Board Layout Figure 3−3.
This page intentionally left blank 3-4
Chapter 4 This chapter provides the TPS61040EVM-002 schematic and bill of materials. Topic Page 4.1 Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2 4.2 Bill of Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Schematic 4.1 Schematic L1 10 µ H J1 1 2 VIN 1 C1 4.7µ F On JP1 D1 MBR0530 J4 D2 U1 TPS61040DBV 5 VIN SW 1 2 GND 3 4 EN FB 1 D3 1 D4 LED ANODE C3 0.1µ F D6 MMBZ5254BLT1 1 Off D5 J2 1 2 147 kΩ R2 249 kΩ J3 DIM1 DIM2 GND J5 1 R3 1 2 GND 1 2 1 2 3 R4 100 Ω LED CATHODE J6 1 2 R1 10 kΩ GND C2 1µF 1 Open 4.2 Bill of Materials Qty Reference Designator Description Size MFR Part Number 1 C2 Capacitor, ceramic, 1.0 µF, 6.
