LM3406HVEVAL/NOPB

User's Guide SNVA407B – August 2009 – Revised May 2013 AN-1993 LM3406HV Evaluation Board with 2 Wire Dimming 1 Introduction The LM3406HV is a buck regulator controlled current source designed to drive a series string of high power, high brightness LEDs (HBLEDs) such as the Luxeon™ K2 Emitter at forward currents of up to 1.5A. The converter's output voltage adjusts as needed to maintain a constant current through the LED array. Figure 1. Complete Circuit Schematic All trademarks are the property of their respective owners. SNVA407B – August 2009 – Revised May 2013 Submit Documentation Feedback AN-1993 LM3406HV Evaluation Board with 2 Wire Dimming Copyright © 2009–2013, Texas Instruments Incorporated 1 Circuit Performance 2 www.ti.com Circuit Performance The LM3406HV circuit and BOM that come pre-installed on the evaluation board are optimized to run from an input voltage of 24V, but the circuit can operate from a wide input voltage range of 6.0V to 75V. The current output ranges from 0.35A to 1.5A. Figure 2 shows the program jumper settings used to program currents of 0.35A, 0.7A, 1A, and 1.5A. 350 mA 1000 mA 700 mA 1500 mA Figure 2. Setting Output Current, J2 The LM3406HV is a step-down regulator with an output voltage range extending from a VO-MIN of 200 mV (the reference voltage) to a VO-MAX determined by the ratio of the minimum off time (typically 230 ns) to the switching frequency. The regulator can maintain the output current through any number of LEDs as long as the combined forward voltage of the array does not exceed VO-MAX . VO-MAX can be calculated with the following formula: VO-MAX = VIN-MIN x (1 - fSW x tOFF-MIN) (1) For example, if VIN is 24V ±10%, then VIN-MIN is 21.6V. For a switching frequency of 500 kHz the maximum output voltage for the converter is 21.6 x [1 - (5 x 105) x (230 x 10-9 ) = 19.1V. Output voltage is calculated with the following formula: VO = n x VF + 0.2V where • • • n is the number of series-connected LEDs VF is the forward voltage of each LED 0.2V represents the voltage across the current sense resistor (2) For InGaN LEDs (white, blue, blue-green) VF is typically 3.5V, and with a limit of (19.1 - 0.2) = 18.9V the LM3406HV could drive as many as five in series. For AlInGaP LEDs (red, orange, amber) VF is typically 2.5V, so a VO-MAX of 18.9V would allow as many as seven to be driven in series. 3 Connecting the LED Array The LM3406HV Evaluation Board includes test posts for connecting the LED/LED Array. Connect the open anode of the array to LED+ and the cathode of the array to CS/LED-. Keep the leads from the board to the LED(s) as short as possible to minimize inductance. 4 Setting the LED Current The default forward current IF delivered to the LED array when no program jumper is installed on J2 is 0.35A, set by resistor R6. The higher LED currents are set when the program jumper puts resistors R4, R5 or R7 in parallel with R6. For users that wish to program a current other than one of the four default levels, or for users who want the best accuracy at a given current, the program jumper J2 should be removed, and R6 changed according to the following equation: 2 AN-1993 LM3406HV Evaluation Board with 2 Wire Dimming SNVA407B – August 2009 – Revised May 2013 Submit Documentation Feedback Copyright © 2009–2013, Texas Instruments Incorporated Pulse Width Modulation (PWM) Dimming www.ti.com R.35 = 0.2 / IF (3) This resistor should be rated to handle the power dissipation of the LED current. For example, the closest 5% tolerance resistor to set an LED current of 0.35A is 0.56Ω. In steady state this resistor will dissipate (0.352 x 0.56) = 69 mW, indicating that a resistor with a 1/8W rating is more than capable of dissipating the power. 5 Pulse Width Modulation (PWM) Dimming The DIM1 terminal on the PCB provides an input for a logic-level pulse width modulation signal for dimming of the LED array. In order to fully enable and disable the LM3406HV the PWM signal should have a maximum logic low level of 0.8V and a minimum logic high level of 2.2V. Graphical representations of minimum and maximum PWM duty cycle are illustrated in Figure 3. The interval tD represents the delay from a logic high at the DIM pin to the rise in output current. The quantities tSU and tSD represent the time needed for the output current to slew up to steady state and slew down to zero, respectively. It is important to note that tD is a property of the LM3406HV and remains fixed in all applications. The slew rates tSU and tSD are a function of the external circuit parameters VIN, VO, IF, inductance (L) and the LM3406HV parameter tOFF-MIN. Response times for a circuit driving three white LEDs at 1A from 24V are shown in the Typical Performance Characteristics section, but the user should test every new circuit to determine the actual PWM dimming response. T T DIM D tD tSU T DMIN tSD tD DMAX tD tSU tSD tSU tSD IF T= 1 DMIN = f PWM t D + t SU T D MAX = T - t SD T Figure 3. PWM Dimming Limits The logic of DIM1 is active low, hence the LM3406HV will deliver regulated output current when the voltage at DIM1 is high, and the current output is disabled when the voltage at DIM1 is low. Connecting a constant logic low will disable the output. Note that an internal pullup esnures that the LM3406HV is enabled if the DIM pin is open-circuited. The DIM1 function disables only the power MOSFET, leaving all other circuit blocks functioning to minimize the converter response time, tD. The DIM2 terminal provides a second method for PWM dimming by connecting to the gate of MOSFET Q1 through the driver U5. Q1 provides a parallel path for the LED current. Shunting the output current through a parallel MOSFET reduces the PWM dimming delays because the inductor current remains continuous, providing faster response time for higher frequency and/or greater resolution in the PWM dimming signal. The trade-off in this method is that the full current flows through Q1 while the LED is off, resulting in lower efficiency. The LM3406HV evaluation board includes an output capacitor to reduce output current ripple which is not initially populated, but the drawback of this output capacitor if used is that it causes significant delays when using parallel MOSFET dimming. The output capacitor should be removed to take full advantage of parallel MOSFET dimming. SNVA407B – August 2009 – Revised May 2013 Submit Documentation Feedback AN-1993 LM3406HV Evaluation Board with 2 Wire Dimming Copyright © 2009–2013, Texas Instruments Incorporated 3 2 Wire Input Dimming www.ti.com The logic of DIM2 is active low, hence the regulated output current flows through the LED array when the voltage at DIM2 is high, and the current flows through the shunt FET when the voltage at DIM2 is low. Connecting a constant logic low to the DIM2 will turn off the LED but will not shut down the LM3406HV. A voltage of up to 30V must be applied to the DPWR pin to operate U5. 6 2 Wire Input Dimming The LM3406HV evaluation board has been designed for 2 wire dimming for systems that present a square wave input voltage for dimming purposes. A diode, D2, separates the VIN pins from the VINS pin. When the input voltage at VINS falls to 70% or less of the voltage at VIN the device stops switching and enters dim mode. The capacitors C1 and C2 hold up the voltage at the VIN pins during this time so that the LM3406HV is enabled and responds quickly when the voltage at VINS again exceeds 70% of the voltage at VIN. 7 Low Power Shutdown The LM3406HV can be placed into a low power shutdown (typically 240 µA) by grounding the OFF* terminal. During normal operation this terminal should be left open-circuit. 8 Output Open Circuit The LM3406HV will begin to operate as soon as VIN is greater than 6V and the DIM and RON pins are not grounded. If the regulator is powered and enabled but no LED array is connected, the output voltage will rise to VIN. The output of the circuit is rated to 50V (beyond the maximum input voltage) and will not suffer damage, however care should be taken not to connect an LED array if the output voltage is higher than the target forward voltage of the LED array in steady state. If the LEDs are disconnected or one of the LEDs fails open-circuit while the LM3406HV is operating, the output voltage will experience a surge as the current in the output inductor seeks a discharge path. The output capacitor (if present) can absorb some of this energy, however circuits with little or no output capacitance can experience a voltage spike that exceeds the rating of the VOUT pin. The evaluation board uses a 10 kΩ resistor in series with the VOUT pin to limit current flowing into the pin. Alternatively, a diode connected from VIN to VO as shown in Figure 4 will clamp the spike to VIN plus a diode drop and is included on the evaluation board. D2 CB VIN VIN BOOT RON CIN L1 VO SW D1 RON LM3406HV VOUT DIM COMP CS GND CC RSNS VCC CF Figure 4. Schottky Diode Protection for Open-Circuit 4 AN-1993 LM3406HV Evaluation Board with 2 Wire Dimming SNVA407B – August 2009 – Revised May 2013 Submit Documentation Feedback Copyright © 2009–2013, Texas Instruments Incorporated Bill of Materials www.ti.com 9 Bill of Materials ID Part Number Type Size Parameters Qty Vendor U1 LM3406HV Buck LED Driver TSSOP-14 75V, 1.5A 1 NSC U5 FDC6333C MOSFET NCH/P-CH SSOT-6 30V, 2.5A 1 Fairchild Semiconductor D1 B1100-13-F Schottky Diode SMA 100V, 1A 1 Diodes Inc. D2, D3 MBRS3100T3G Schottky Diode SMC 100V, 3A 2 ON Semiconductor Q1 SI4464DY-E3 MOSFET SOIC-8 200V, 1.7A 1 Vishay C1 C2 C5750X7R2A475M Capacitor 2220 4.7 µF, 100V 2 TDK C3 GRM188R71C223K01D Capacitor 0603 0.022 µF, 16V 1 Murata C4, C5, C7 GRM188R71C104K01D Capacitor 0603 0.1 µF, 16V 3 Murata C6 Capacitor 1812 OPEN L1 MSS1038–333MLB Inductor MSS1038 33 μH, 1.8A 1 Coilcraft R1 CRCW0805143kFKA Resistor 0805 143 kΩ 1% 1 Vishay R2 CRCW06031K00JNEA Resistor 0603 1 kΩ 5% 1 Vishay R3 CRCW060310k0FKA Resistor 0603 10 kΩ 1% 1 Vishay R4 ERJ-6RQFR30V Resistor 0805 0.3 Ω 1% 1 Panasonic R5 ERJ-6RQFR16V Resistor 0805 0.16 Ω 1% 1 Panasonic R6 ERJ-6RQFR56V Resistor 0805 0.56 Ω 1% 1 Panasonic R7 ERJ-6RQFR62V Resistor 0805 0.62 Ω 1% 1 Panasonic 1 Ω 1% R8, R9 CRCW06031R00FNEA Resistor 0603 2 Vishay CS/LED, DIM1, DIM2, DPWR, GND2, LED+, OFF*, SW 1502–2 Terminal Keystone 1598–2 8 Keystone VIN, GND 575–8 Terminal 575–8 2 Keystone SNVA407B – August 2009 – Revised May 2013 Submit Documentation Feedback AN-1993 LM3406HV Evaluation Board with 2 Wire Dimming Copyright © 2009–2013, Texas Instruments Incorporated 5 Typical Performance Characteristics 10 www.ti.com Typical Performance Characteristics VIN = 24V, IF = 1A, TA = 25°C, and the load consists of three InGaN LEDs in series unless otherwise noted. Efficiency vs. Number of InGaN LEDs in Series Efficiency vs Output Current IF vs VIN IF vs TA OUTPUT CURRENT (A) 1.0 0.8 0.6 0.4 0.2 0.0 0.0 16.0 32.0 48.0 64.0 80.0 INPUT VOLTAGE (V) 6 AN-1993 LM3406HV Evaluation Board with 2 Wire Dimming SNVA407B – August 2009 – Revised May 2013 Submit Documentation Feedback Copyright © 2009–2013, Texas Instruments Incorporated Typical Performance Characteristics www.ti.com Switching Frequency vs Number of InGaN LEDs in Series Switching Frequency vs VIN SWITCHING FREQUENCY (kHz) 600.0 480.0 360.0 240.0 120.0 0.0 0.0 16.0 32.0 48.0 64.0 80.0 INPUT VOLTAGE (V) Switch Node and Output Current (DC Coupled) Output Current (AC Coupled) 0.5A/DIV IF IF SW 20 mA/DIV 10V/DIV 1 és/DIV 1 és/DIV DIM1 Response (Rising) DIM1 Response (Falling) 0.5A/DIV IF 0.5A/DIV IF 20V/DIV SW DIM1 SW 5V/DIV DIM1 2 és/DIV SNVA407B – August 2009 – Revised May 2013 Submit Documentation Feedback 20V/DIV 5V/DIV 2 és/DIV AN-1993 LM3406HV Evaluation Board with 2 Wire Dimming Copyright © 2009–2013, Texas Instruments Incorporated 7 Typical Performance Characteristics www.ti.com Start Up using OFF Terminal Shutdown using OFF Terminal 0.5A/DIV 0.5A/DIV IF IF 20V/DIV SW OFF 20V/DIV SW 2V/DIV OFF 2V/DIV 2 és/DIV 2 ms/DIV 8 AN-1993 LM3406HV Evaluation Board with 2 Wire Dimming SNVA407B – August 2009 – Revised May 2013 Submit Documentation Feedback Copyright © 2009–2013, Texas Instruments Incorporated Layout www.ti.com 11 Layout Figure 5. Top Layer and Top Overlay SNVA407B – August 2009 – Revised May 2013 Submit Documentation Feedback AN-1993 LM3406HV Evaluation Board with 2 Wire Dimming Copyright © 2009–2013, Texas Instruments Incorporated 9 Layout www.ti.com Figure 6. Bottom Layer and Bottom Overlay 10 AN-1993 LM3406HV Evaluation Board with 2 Wire Dimming SNVA407B – August 2009 – Revised May 2013 Submit Documentation Feedback Copyright © 2009–2013, 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. 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