LM3433SQ-14AEV/NOPB

User's Guide SNVA327B – March 2008 – Revised May 2013 AN-1793 LM3433 4A to 20A LED Driver Evaluation Board 1 Introduction The LM3433 is an adaptive constant on-time DC/DC buck constant current controller designed to drive a high brightness LEDs (HB LED) at high forward currents. It is a true current source that provides a constant current with constant ripple current regardless of the LED forward voltage drop. The board can accept an input voltage ranging from -9V to -14V w.r.t. GND. The output configuration allows the anodes of multiple LEDs to be tied directly to the ground referenced chassis for maximum heat sink efficacy when a negative input voltage is used. 2 LM3433 Board Description The evaluation board is designed to provide a constant current in the range of 4A to 20A. The LM3433 requires two input voltages for operation. A positive voltage with respect to GND is required for the bias and control circuitry and a negative voltage with respect to GND is required for the main power input. This allows for the capability of using common anode LEDs so that the anodes can be tied to the ground referenced chassis. The evaluation board only requires one input voltage of -12V with respect to GND. The positive voltage is supplied by the LM5002 circuit. The LM5002 circuit also provides a UVLO function to remove the possibility of the LM3433 from drawing high currents at low input voltages during startup. Initially the output current is set at the minimum of approximately 4A with the POT P1 fully counterclockwise. To set the desired current level a short may be connected between LED+ and LED-, then use a current probe and turn the POT clockwise until the desired current is reached. PWM dimming FETs are included on-board for testing when the LED can be connected directly next to the board. A shutdown test post on J2, ENA, is included so that startup and shutdown functions can be tested using an external voltage. 3 Setting the LED Current The LM3433 evaluation board is designed so that the LED current can be set in multiple ways. There is a shunt on J2 initially connecting the ADJ pin to the POT allowing the current to be adjusted using the POT P1. This POT will apply a voltage to the ADJ pin between 0.3V and 1.5V w.r.t. GND to adjust the voltage across the sense resistor (RSENSE) R15. The shunt may also be removed and an external voltage positive w.r.t. GND can then be applied to the ADJ test point on the board. A 5mΩ resistor comes mounted on the board so using the VSENSE vs. VADJ graph in the Section 6 section the current can be set using Equation 1: ILED = VSENSE/RSENSE (1) Alternatively the shunt can be removed and connect the ADJ test point can be connected to the VINX test point to fix VSENSE at 60mV. 4 PWM Dimming The LM3433 is capable if high speed PWM dimming in excess of 40kHz. Dimming is accomplished by shorting across the LED with a FET(s). Dimming FETs are included on the evaluation board for testing LEDs placed close to the board. The FETs on the evaluation board should be removed if using dimming FETs remotely placed close to the LED (recommended). All trademarks are the property of their respective owners. SNVA327B – March 2008 – Revised May 2013 Submit Documentation Feedback AN-1793 LM3433 4A to 20A LED Driver Evaluation Board Copyright © 2008–2013, Texas Instruments Incorporated 1 High Current Operation and Component Lifetime www.ti.com To use the dimming function apply square wave to the PWM test point on the board that has a positive voltage w.r.t. GND. When this pin is pulled high the dimming FET is enabled and the LED turns off. When it is pulled low the dimming FET is turned off and the LED turns on. A scope plot of PWM dimming is included in the Typical Performance Characteristics section showing 30kHz dimming at 50% duty cycle. 5 High Current Operation and Component Lifetime When driving high current LEDs, particularly when PWM dimming, component lifetime may become a factor. In these cases the input ripple current that the input capacitors are required to withstand can become large. At lower currents long life ceramic capacitors may be able to handle this ripple current without a problem. At higher currents more input capacitance may be required. To remain cost effective this may require putting one or more aluminum electrolytic capacitors in parallel with the ceramic input capacitors. Since the operational lifetime of LEDs is very long (up to 50,000 hours) the longevity of an aluminum electrolytic capacitor can become the main factor in the overall system lifetime. The first consideration for selecting the input capacitors is the RMS ripple current they will be required to handle. This current is given by Equation 2: IRMS = ILED VLED(|VEE|-VLED) |VEE| (2) The parallel combination of the ceramic and aluminum electrolytic input capacitors must be able to handle this ripple current. The aluminum electrolytic in particular should be able to handle the ripple current without a significant rise in core temperature. A good rule of thumb is that if the case temperature of the capacitor is 5°C above the ambient board temperature then the capacitor is not capable of sustaining the ripple current for its full rated lifetime and a more robust or lower ESR capacitor should be selected. The other main considerations for aluminum electrolytic capacitor lifetime are the rated lifetime and the ambient operating temperature. An aluminum electrolytic capacitor comes with a lifetime rating at a given core temperature, such as 5000 hours at 105°C. As dictated by physics the capacitor lifetime should double for each 7°C below this temperature the capacitor operates at and should halve for each 7°C above this temperature the capacitor operates at. A good quality aluminum electrolytic capacitor will also have a core temperature of approximately 3°C to 5°C above the ambient temperature at rated RMS operating current. So as an example, a capacitor rated for 5,000 hours at 105°C that is operating in an ambient environment of 85°C will have a core temperature of approximately 90°C at full rated RMS operating current. In this case the expected operating lifetime of the capacitor will be approximately just over 20,000 hours. The actual lifetime (LifeACTUAL) can be found using Equation 3: (T LifeACTUAL = LifeRATED X 2 CORE - TACTUAL 7 ) (3) Where LifeRATED is the rated lifetime at the rated core temperature TCORE. For example, if the ambient temperature is 85°C the core temperature is 85°C + 5°C = 90°C. (105°C - 90°C)/7°C = 2.143. 2^2.413 = 4.417. So the expected lifetime is 5,000*4.417 = 22,085 hours. Long life capacitors are recommended for LED applications and are available with ratings of up to 20,000 hours or more at 105°C. 2 AN-1793 LM3433 4A to 20A LED Driver Evaluation Board Copyright © 2008–2013, Texas Instruments Incorporated SNVA327B – March 2008 – Revised May 2013 Submit Documentation Feedback High Current Operation and Component Lifetime www.ti.com Figure 1. LM3433 Evaluation Board Schematic SNVA327B – March 2008 – Revised May 2013 Submit Documentation Feedback AN-1793 LM3433 4A to 20A LED Driver Evaluation Board Copyright © 2008–2013, Texas Instruments Incorporated 3 High Current Operation and Component Lifetime www.ti.com Table 1. Bill of Materials (BOM) 4 Qty ID Part Number Type Size 1 U1 LM3433 LED Driver WQFN-24 Parameters Vendor TI 1 U2 LM5002 Boost Regulator SOIC-8 TI 1 C1 C0805C331J5GACTU Capacitor 0805 330pF, 50V Kemet 1 C2 GRM31CR60J476KE19L Capacitor 1206 47µF, 6.3V Murata 1 C3 16SA150M Capacitor MULTICAP 150µF, 16V Sanyo 2 C4, C5 GRM32ER61C226KE20L Capacitor 1210 22µF, 16V Murata 1 C6 GRM32ER61C476ME15L Capacitor 1210 47µF, 16V Murata 1 C7 C0805C104J5RACTU Capacitor 0805 0.1µF, 50V Kemet 2 C8, C13 HMK212BJ103KG-T Capacitor 0805 10nF, 100V Taiyo Yuden C9 OPEN 2 C10, C11 GRM21BR61C475KA Capacitor 0805 4.7µF, 16V Murata 1 C12 0805YD105KAT2A Capacitor 0805 1µF, 16V AVX 1 C14 B37941K9474K60 Capacitor 0805 0.47µF, 16V EPCOS Inc . 1 C15 GRM21BF51E225ZA01L Capacitor 0805 2.2µF, 25V Murata C17 OPEN 1 C18 08055C104JAT2A Capacitor 0805 0.1µF, 50V AVX 2 D1, D2 MA2YD2600L Diode SOD-123 60V, 800mA Panasonic 1 D3 MBRS240LT3 Diode SMB 40V, 2A ON Semiconductor 0805 0805 D4 OPEN 1 J2 B8B-EH-A(LF)(SN) Connector SMB 1 J1 1761582001 Connector 1 J9 TFML-110-02-S-D Connector TFM-110-02X-D-LC 1 L1 LPS3008-104ML Inductor 3008 JST Sales America, Inc. Weidmuller Samtec 100µH, 150mA Coilcraft 1 L2 GA3252-AL Inductor GA3252-AL 12µH, 14A Coilcraft 4 L3, L4, L5, L6 MPZ2012S300A Ferrite Bead 0805 30Ω @ 100MHz TDK 1 L7 MPZ2012S101A Ferrite Bead 0805 100Ω @ 100MHz TDK 1 P1 3352T-1-103LF Potentiometer BOURNS2 10kΩ Bourns 1 P10 3429-6002 Connector HDR13x2 13X2 Pin Header 3M 2 Q1, Q2, Q3, Q4, Q5, Q6 NTMFS4841NH FET PowerPAK 30V, 11mΩ ON Semiconductor 1 Q7 BC856S Dual PNP SOT363_N Phillips 1 Q8 ZXTN25040DFHTA NPN SOT-23B Zetex Inc. 1 Q9 ZXTP25040DFHTA PNP SOT-23B 1 R1 ERJ-6ENF2942V Resistor 0805 29.4kΩ Panasonic 1 R2 ERJ-6ENF2491V Resistor 0805 2.49kΩ Panasonic 3 R3, R30, R31 ERJ-6ENF1002V Resistor 0805 10kΩ Panasonic 1 R4 ERJ-6GEYJ393V Resistor 0805 39kΩ Panasonic 1 R5 ERJ-6GEYJ101V Resistor 0805 100Ω Panasonic R7 OPEN 2 R14 ERJ-6GEY0R00V Resistor 0805 0Ω Panasonic 1 R8 ERJ-6ENF2002V Resistor 0805 20kΩ Panasonic 1 R10 ERJ-6ENF4991V Resistor 0805 4.99kΩ Panasonic 2 R11, R12 ERJ-6ENF6192V Resistor 0805 61.9kΩ Panasonic 1 R13 ERJ-6GEYJ103V Resistor 0805 10kΩ Panasonic AN-1793 LM3433 4A to 20A LED Driver Evaluation Board Copyright © 2008–2013, Texas Instruments Incorporated Zetex Inc. SNVA327B – March 2008 – Revised May 2013 Submit Documentation Feedback High Current Operation and Component Lifetime www.ti.com Table 1. Bill of Materials (BOM) (continued) Qty ID Part Number Type Size Parameters Vendor 1 R15 WSL25125L000FEA Resistor CR6332-2512 0.005Ω Vishay 6 R16, R17, R18, R19, R20, R21 ERJ-6GEYJ2R7V Resistor 0805 2.7Ω Panasonic 1 R22 ERJ-6GEYJ100V Resistor 0805 10Ω Panasonic 1 R25 ERJ-6ENF7502V Resistor 0805 75kΩ Panasonic R26 OPEN 2 LED+, LED- 1502-2 Test Post TP 1502 0.109" Keystone 3 ADJ, PWM, VINX 1593-2 Test Post TP 1593 0.084" Keystone SNVA327B – March 2008 – Revised May 2013 Submit Documentation Feedback 0805 AN-1793 LM3433 4A to 20A LED Driver Evaluation Board Copyright © 2008–2013, Texas Instruments Incorporated 5 Typical Performance Characteristics 6 www.ti.com Typical Performance Characteristics 97 96 2A 4A 6A 8A 96 94 94 EFFICIENCY (%) EFFICIENCY (%) 95 93 92 91 90 2A 4A 6A 8A 89 88 87 1 2 3 4 5 6 92 90 88 86 84 7 1 2 3 VLED (V) 6 7 Figure 3. Efficiency vs. LED Forward Voltage (VCGND - VEE = 12V) 100 96 2A 4A 6A 8A 94 90 80 70 VSENSE (mV) 92 EFFICIENCY (%) 5 VLED (V) Figure 2. Efficiency vs. LED Forward Voltage (VCGND - VEE = 9V) 90 88 86 60 50 40 30 84 20 82 10 80 1 2 3 4 5 6 7 0 0.2 0.4 Figure 4. Efficiency vs. LED Forward Voltage (VCGND - VEE = 14V) 0.6 0.8 1 1.2 1.4 1.6 ADJ VOLTAGE (V) VLED (V) 6 4 Figure 5. VSENSE vs. VADJ AN-1793 LM3433 4A to 20A LED Driver Evaluation Board Copyright © 2008–2013, Texas Instruments Incorporated SNVA327B – March 2008 – Revised May 2013 Submit Documentation Feedback Typical Performance Characteristics www.ti.com ILED = 6A nominal, VIN = 3.3V, VEE = -12V Top trace: DIM input, 2V/div, DC Bottom trace: ILED, 2A/div, DC T = 10µs/div Figure 6. 30kHz PWM Dimming Waveform Showing Inductor Ripple Current SNVA327B – March 2008 – Revised May 2013 Submit Documentation Feedback AN-1793 LM3433 4A to 20A LED Driver Evaluation Board Copyright © 2008–2013, Texas Instruments Incorporated 7 Layout 7 www.ti.com Layout Figure 7. Top Layer and Top Overlay 8 AN-1793 LM3433 4A to 20A LED Driver Evaluation Board Copyright © 2008–2013, Texas Instruments Incorporated SNVA327B – March 2008 – Revised May 2013 Submit Documentation Feedback Layout www.ti.com Figure 8. Upper Middle Layer SNVA327B – March 2008 – Revised May 2013 Submit Documentation Feedback AN-1793 LM3433 4A to 20A LED Driver Evaluation Board Copyright © 2008–2013, Texas Instruments Incorporated 9 Layout www.ti.com Figure 9. Lower Middle Layer 10 AN-1793 LM3433 4A to 20A LED Driver Evaluation Board Copyright © 2008–2013, Texas Instruments Incorporated SNVA327B – March 2008 – Revised May 2013 Submit Documentation Feedback Layout www.ti.com Figure 10. Bottom Layer and Bottom Overlay SNVA327B – March 2008 – Revised May 2013 Submit Documentation Feedback AN-1793 LM3433 4A to 20A LED Driver Evaluation Board Copyright © 2008–2013, Texas Instruments Incorporated 11 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. 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