LM3404MREVAL

User's Guide SNVA220C – May 2007 – Revised April 2013 AN-1585 LM3402 and LM3404 High Power SO PowerPAD-8 Evaluation Board 1 Introduction The LM3402/02HV and LM3404/04HV are buck-regulator derived, controlled current sources 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 0.5A (LM3402/02HV) or 1.0A (LM3404/04HV). This evaluation board demonstrates the enhanced thermal performance of the SO PowerPAD-8 package option of any of those four ICs. The LM3404 was chosen for the example circuit because the combination of high output current, high input voltage, and high duty cycle create the greatest demand for low junction-to-ambient thermal resistance (θJA). Note that the LM3404/04HV in SO-8 can also be used with this evaluation board, with reduced thermal performance. LED drivers are often placed in small, closed spaces with no air flow and high ambient temperature due to the dissipation of the LEDs. When properly soldered the SO PowerPAD-8 package offers a θJA that is as little as one-half that of the standard SO-8 package, and as little as one-third that of the MSOP-8 package. 2 Circuit Performance with LM3404 This evaluation board uses the LM3404 to provide a constant forward current of 1.0A ±10% to a string of ten series-connected HBLEDs with a forward voltage of approximately 3.7V each from an input of 48V ±5%. The LED ripple current, ΔiF, will not exceed 80 mAP-P, and the switching frequency is 550 kHz ± 10%. The circuit can operate over an extended input voltage range of 40V to 60V, however output current may exceed the ±10% specification. CB 10 nF VIN = 48V ±5% L1 VIN CIN1 CIN2 2.2 PF 2.2 PF BOOT SW RON 47 PH Vo/LED+ D1 536 k: CO RON 0.47 PF LM3404HV CS/LED- CS OFF RSNS DIM DIM GND 0.2: VCC CF 0.1 PF Figure 1. Standard Schematic All trademarks are the property of their respective owners. SNVA220C – May 2007 – Revised April 2013 Submit Documentation Feedback AN-1585 LM3402 and LM3404 High Power SO PowerPAD-8 Evaluation Board Copyright © 2007–2013, Texas Instruments Incorporated 1 Thermal Performance 3 www.ti.com Thermal Performance The SO PowerPAD-8 package is pin-for-pin compatible with the SO-8 package with the exception of the thermal pad, or exposed die attach paddle (DAP). The DAP is electrically connected to system ground. When the DAP is properly soldered to an area of copper on the top layer, bottom layer, internal planes, or combinations of various layers, the θJA of the LM3404/04HV can be significantly lower than that of the SO8 package or VSSOP-8 package in the case of the LM3402/02HV. The SO PowerPAD-8 evaluation board is two layers of 1oz copper each, and measures 1.25" by 1.95". The DAP is soldered to approximately one square inch of top and two square inches of bottom layer copper. Five thermal vias connect the DAP to the bottom layer of the PCB, and the recommended DAP/via layout is shown in Figure 2. 90 mil 10 mil 10 mil 90 mil 35 mil 35 mil Figure 2. Thermal Pad and Via Layout Calibrated testing was performed on the SO PowerPAD-8 evaluation board to compare the performance of the SO PowerPAD-8 with the DAP soldered and the standard SO-8 package. The example circuit dissipation is approximately 1.1W. (see the LM3404/04HV datasheet for detailed thermal calculations.) For dissipation ranging from 0.5W to 1.5W the θJA of the SO PowerPAD-8 package is 50°C/W ±10%. The θJA of the SO-8 package is 100°C/W ±10%. 4 Connecting to LED Array The LM3404/04HV Evaluation Board includes a female 6-pin SIP, J1, connector as well as two standard 94mil turret connectors for the cathode and anode connections of the LED array. Figure 3 shows the pinout of J1. Solid 18 or 20 gauge wire with about 1 cm of insulation stripped away makes a convenient, solderless connection to J1. P6 Cathode of Last LED C535676 Connector P1 Anode of First LED Figure 3. LED Connector 5 Setting the LED Current The default forward current IF delivered to the LED array is 1.0A, typical of many 3W LEDs. To adjust this value the current setting resistor RSNS can be changed according to the following equation: 2 AN-1585 LM3402 and LM3404 High Power SO PowerPAD-8 Evaluation Board Copyright © 2007–2013, Texas Instruments Incorporated SNVA220C – May 2007 – Revised April 2013 Submit Documentation Feedback PWM Dimming www.ti.com 0.2 x L RSNS = IF x L + VO x tSNS - VIN - VO x tON 2 (1) (2) tSNS = 220 ns This resistor should be rated to handle the power dissipation of the LED current. For this example, the closest 5% tolerance resistor to set an LED current of 1.0A is 0.2 Ω. In steady state this resistor will dissipate (1.0 x 0.2) = 200 mW, indicating that a resistor with a 1/4W power rating is appropriate. 6 PWM Dimming The DIM terminal on the PCB provides an input for a pulse width modulation signal for dimming of the LED array. In order to fully enable and disable the LM3404/04HV the PWM signal should have a maximum logic low level of 0.8V and a minimum logic high level of 2.2V. The maximum PWM dimming frequency, minimum PWM duty cycle and maximum duty cycle are illustrated in Figure 4. PWM frequency should be at least one order of magnitude below the LM3404/04HV switching frequency. The interval tD represents the delay from a logic high at the DIM pin to the onset of the 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. Typical response time is shown in Typical Performance Characteristics. T T T DIM D tD DMIN tSD tSU tD DMAX tSU tSD tD tSU tSD IF T= 1 fPWM DMIN = T - tSD tD + tSU T DMAX = T Figure 4. PWM Dimming Limits The logic of DIM is direct, hence the LM3404 will deliver regulated output current when the voltage at DIM is high, and the current output is disabled when the voltage at DIM is low. Connecting a constant logic low will disable the output, and the LM3404/04HV is enabled if the DIM pin is open-circuited. The DIM function disables only the power MOSFET, leaving all other circuit blocks functioning to minimize the converter response time. SNVA220C – May 2007 – Revised April 2013 Submit Documentation Feedback AN-1585 LM3402 and LM3404 High Power SO PowerPAD-8 Evaluation Board Copyright © 2007–2013, Texas Instruments Incorporated 3 Low Power Shutdown 7 www.ti.com Low Power Shutdown The LM3404 can be placed into a low power shutdown (IQ typically 90 µA) by grounding the OFF* terminal. During normal operation this terminal should be left open-circuit. 8 Bill of Materials Table 1. Bill of Materials 4 ID Part Number Type Size Parameters Qty Vendor U1 LM3404 LED Driver SO PowerPAD-8 75V, 1.0A 1 NSC L1 SLF10145T- 470M1R4 Inductor 10.1 x 10.1 x 4.5mm 47µH, 1.4A, 0.1Ω 1 TDK D1 CMSH2-60M Schottky Diode SMA 60V, 2A 1 Central Semi Cf VJ0603Y104KXXAT Capacitor 0603 100nF 10% 1 Vishay Cb VJ0603Y103KXXAT Capacitor 0603 10nF 10% 1 Vishay Cin1, Cin2 C4532X7R2A225M Capacitor 1812 2.2µF, 100V 2 TDK Co C3216X7R2A474M Capacitor 1206 0.47µF, 100V 1 TDK Rsns ERJ8BQFR20V Resistor 1206 0.2Ω 1% 1 Panasonic Ron CRCW06035363F Resistor 0603 536kΩ 1% 1 Vishay DIM1, OFF* 160-1512 Terminal 0.062” 2 Cambion GND, VIN, Vo/LED+, CS/LED- 160-1026 Terminal 0.094” 5 Cambion J1 535676-5 Connector Custom 1 Tyco/AMP AN-1585 LM3402 and LM3404 High Power SO PowerPAD-8 Evaluation Board Copyright © 2007–2013, Texas Instruments Incorporated 6 Pins SNVA220C – May 2007 – Revised April 2013 Submit Documentation Feedback Typical Performance Characteristics www.ti.com 9 Typical Performance Characteristics DIM Pin Enable DIM DIM Pin Disable DIM 5V/Div 5V/Div 200 mA/Div 200 mA/Div IF IF 2 Ps/DIV 4 Ps/DIV Switching Waveforms Output Ripple Current 200 mA/Div 20 mA/Div IF IF SW 10V/Div 1 Ps/DIV SNVA220C – May 2007 – Revised April 2013 Submit Documentation Feedback 1 Ps/DIV AN-1585 LM3402 and LM3404 High Power SO PowerPAD-8 Evaluation Board Copyright © 2007–2013, Texas Instruments Incorporated 5 Layout 10 www.ti.com Layout Figure 5. Top Layer and Top Overlay Figure 6. Bottom Layer and Bottom Overlay 6 AN-1585 LM3402 and LM3404 High Power SO PowerPAD-8 Evaluation Board Copyright © 2007–2013, Texas Instruments Incorporated SNVA220C – May 2007 – Revised April 2013 Submit Documentation Feedback 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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