LM3405XEVAL

User's Guide SNVA222A – March 2007 – Revised April 2013 AN-1590 LM3405 Demo Board 1 Introduction The LM3405 demo board is configured to drive a series string of high power, high brightness LEDs at a forward current of 1A using the LM3405 constant current buck regulator. The board can accept a full input operating range of 3V to 15V. The converter output voltage adjusts as needed to maintain a constant current through the LED array. The LM3405 is a step-down regulator with an output voltage range extending from a VO(MIN) of 205mV (the reference voltage) to a VO(MAX) determined by the maximum duty cycle (typically 94%). It can drive up to 3 LEDs in series at 1A forward current, with the single LED forward voltage of approximately 3.7V (Typical of white, blue, and green LEDs using InGaN technology). As shown in the demo board schematic circuit in Figure 1, the board is configured with the boost voltage derived from VIN through a shunt zener (D3). This will ensure that the gate drive voltage VBOOST - VSW falls in the recommended range of 2.5V to 5.5V when VIN varies from 5V to 15V. In cases of low input voltages (3V to 5V) being used, the boost diode (D2) can be directly connected to VIN (R3 short, C4 and D3 not installed) to obtain sufficient gate drive voltage for best performance. Table 1 lists the bill of materials of this demo board. The measured performance characteristics and layout of this board are also included below. Additional Circuit Configuration Schematics section illustrates other possible circuit configurations of this board to accommodate various input and output requirements as discussed in the LM3405 datasheet. 2 Connecting to LED Array The LM3405 Demo Board includes a female 6-position SIP connector P1 as well as two standard 72mil turret connectors for the cathode and anode connections of the LED array. Solid 18 or 20 gauge wire with about 1cm of insulation stripped away makes a convenient, solderless connection to P1. 3 Setting the LED Current The default forward current IF delivered to the LED array is 1.0A. To adjust this value the current setting resistor R1 can be changed according to the following equation: IF = VFB / R1 (1) The feedback voltage VFB is regulated at 0.205V typically. The resistor R1 should be rated to handle the power dissipation of the LED current. R1 should be less than approximately 1Ω, to ensure that the LED current is kept above 200mA. If average LED currents of less than 200mA are desired, the EN/DIM pin should be used for PWM dimming. 4 PWM Dimming The default connection of the PWM terminal is tied to VIN through a 100kΩ resistor (R2) to enable the chip, which allows the set current to flow through the LEDs continuously. This PWM terminal can also be connected separately to a periodic pulse signal at different frequencies and/or duty cycle for PWM dimming. A typical LED current waveform in PWM dimming mode is shown in Figure 2. Figure 3 shows the average LED current versus duty cycle of PWM dimming signal for various frequencies. Due to an approximately 100µs delay between the dimming signal and LED current, the dimming ratio reduces dramatically if the applied PWM dimming frequency is greater than 5kHz. All trademarks are the property of their respective owners. SNVA222A – March 2007 – Revised April 2013 Submit Documentation Feedback AN-1590 LM3405 Demo Board Copyright © 2007–2013, Texas Instruments Incorporated 1 PWM Dimming www.ti.com C4 D4 * D3 R3 D2 5 VIN BOOST VIN 1 C3 C1 SW R2 6 LM3405 4 PWM VOUT L1 P1 12 2 D1 C2 FB 3 7 GND ANODE of First LED 3 4 C5 EN/DIM GND 1 5 6 IF CATHODE of Last LED FB 2 R1 * Not installed Figure 1. LM3405 Demo Board Schematic Figure 2. PWM Dimming of LEDs 2 Figure 3. Average LED Current versus Duty Cycle of PWM Dimming Signal at PWM Terminal AN-1590 LM3405 Demo Board SNVA222A – March 2007 – Revised April 2013 Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated Bill of Materials www.ti.com 5 Bill of Materials Table 1. Bill of Materials 6 Part ID Part Value Part Number Manufacturer U1 L1 1A constant current buck regulator, SOT-6 LM3405 Texas Instruments 6.8µH, 1.5A, 35mΩ, 6.0 x 6.0 x 2.8mm SLF6028T-6R8M1R5-PF TDK C1 10µF, 25V, X5R, 1206 GRM31CR61E106KA12L Murata C2 1µF, 25V, X7R, 1206 C1206C105K3RACTU Kemet C3 0.01µF, 16V, X7R, 0805 0805YC103KAT2A AVX C4 0.1µF, 16V, X7R, 0805 GRM219R71C104KA01D Murata C5 1µF, 25V, X5R, 0805 GRM216R61E105KA12D Murata D1 Schottky, 30V, 1A, SMA MBRA130LT3G ON Semiconductor D2 Schottky, 30V, 200mA, SOD-323 BAT54WS-TP Micro Commercial Co. D3 5.1V, 0.35W, SOT23 BZX84C5V1 Fairchild Semiconductor D4 Not installed R1 0.5W, 0.2Ω, 1%, 2010 WSL2010R2000FEA Vishay R2 100kΩ, 1/8W, 1%, 0805 CRCW0805100KFKEA Vishay R3 1.0kΩ, 1%, 1/8W, 0805 CRCW08051K00FKEA Vishay P1 6-position connector 5535676-5 Tyco/AMP Typical Performance Characteristics Figure 4. Efficiency vs. LED Current (VIN = 5V, VBOOST Derived from VIN) Figure 5. Efficiency vs. LED Current (VIN = 12V) SNVA222A – March 2007 – Revised April 2013 Submit Documentation Feedback AN-1590 LM3405 Demo Board Copyright © 2007–2013, Texas Instruments Incorporated 3 Typical Performance Characteristics 4 www.ti.com Figure 6. Efficiency vs. Input Voltage (IF = 1A) Figure 7. Switching Waveforms Figure 8. Startup during PWM Dimming (VIN = 12V, IF = 1A) Figure 9. Shutdown during PWM Dimming (VIN = 12V, IF = 1A) AN-1590 LM3405 Demo Board SNVA222A – March 2007 – Revised April 2013 Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated Layout www.ti.com 7 Layout Figure 10. Top Layer and Top Overlay Figure 11. Bottom Layer and Bottom Overlay SNVA222A – March 2007 – Revised April 2013 Submit Documentation Feedback AN-1590 LM3405 Demo Board Copyright © 2007–2013, Texas Instruments Incorporated 5 Layout www.ti.com Figure 12. Internal Plane 1 (GND) Figure 13. Internal Plane 2 (VIN) 6 AN-1590 LM3405 Demo Board SNVA222A – March 2007 – Revised April 2013 Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated Additional Circuit Configuration Schematics www.ti.com 8 Additional Circuit Configuration Schematics D4 D3 C4 R3 D2 5 VIN BOOST VIN 1 C3 C1 SW R2 6 LM3405 4 PWM VOUT L1 D1 C2 EN/DIM FB GND C5 3 GND 2 P1 12 1 2 3 4 5 7 6 LED ANODE LED CATHODE FB R1 Figure 14. VBOOST Derived from VIN D4 D3 C4 R3 D2 5 VIN BOOST VIN 1 C3 C1 SW R2 6 LM3405 PWM 4 D1 VOUT L1 C2 EN/DIM GND FB GND 2 C5 3 P1 12 1 2 3 4 5 7 6 LED ANODE LED CATHODE FB R1 Figure 15. VBOOST Derived from VOUT SNVA222A – March 2007 – Revised April 2013 Submit Documentation Feedback AN-1590 LM3405 Demo Board Copyright © 2007–2013, Texas Instruments Incorporated 7 Additional Circuit Configuration Schematics www.ti.com D4 D3 C4 R3* D2 5 VIN BOOST VIN 1 C3 C1 SW R2 6 LM3405 4 PWM VOUT L1 P1 12 1 LED ANODE 2 D1 C2 3 4 C5 EN/DIM FB GND 3 7 GND 5 6 LED CATHODE FB 2 R1 * a zener diode is connected in R3 spot Figure 16. VBOOST Derived from VIN through a Series Zener Diode D4 D3 C4 R3 D2 5 VIN BOOST VIN 1 C3 C1 SW R2 6 LM3405 4 PWM D1 VOUT L1 C2 EN/DIM FB GND 3 GND 2 C5 P1 12 1 2 3 4 5 7 6 LED ANODE LED CATHODE FB R1 Figure 17. VBOOST Derived from VOUT through a Series Zener Diode 8 AN-1590 LM3405 Demo Board SNVA222A – March 2007 – Revised April 2013 Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment. 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