MIC3205 Evaluation Board High-Brightness LED Driver Controller with Fixed-Frequency Hysteretic Control General Description Getting Started The MIC3205 is a hysteretic, step-down, high-brightness LED (HB LED) driver with a patent pending frequency regulation scheme that maintains a constant operating frequency over input voltage range. It provides an ideal solution for interior/exterior lighting, architectural and ambient lighting, LED bulbs, and other general illumination applications. The board is optimized for ease of testing, with all of the components on a single side. The device operates from a 4.5V to 40V input voltage range, and controls an external power MOSFET to drive high-current LEDs. On-board components are set up to evaluate one 1A current rating LED, at a switching frequency of approximately 400 kHz. To evaluate a different number of LEDs or different current rating LEDs, component values must be changed as explained in the Application Information section of the MIC3205 data sheet. Requirements This board needs a single bench power source adjustable over the input voltage of 4.5V < VIN < 40V that can provide at least 1A of current. The loads can either be active (electronic load) or passive (LEDs) with the ability to dissipate the maximum load power while keeping accessible surfaces ideally < 70°C. Precautions There is no reverse input protection on this board. When connecting the input sources, make sure that the correct polarity is observed. Under extreme load conditions, input transients can be quite large if long test leads are used. In such cases, a 100µF, 63V electrolytic capacitor is needed at the VIN terminals to prevent overvoltage damage to the IC. Datasheets and support documentation can be found on Micrel’s web site at: www.micrel.com. 1. Connect VIN supply to the input terminals VIN and GND. Connect a supply between the VIN terminal (J1) and the GND terminal (J2), paying careful attention to polarity and supply range (4.5V < VIN < 40V). Monitor IIN with a current meter and VIN at the VIN and GND terminals with a voltmeter. Don’t apply power until step 4. 2. Connect the load to the output terminals, LED+ and LED−. Connect a load between the LED+ (J5) and LED– (J6) terminals. The load can be either one 1A rated LED or an active, electronic load. Make sure to connect the anode of the 1A LED to the LED+ terminal and the cathode to the LED– terminal. 3. Enable input. The MIC3205YML EV board comes with a 100kΩ pull-up resistor to VIN. A jumper (JP6) is provided on board for users to easily access the enable feature. Applying an external logic signal on the EN pin to pull it low or using a jumper to short the EN pin to GND shuts off the output of the evaluation board. 4. Turn ON the input supply. By default, the controller is enabled when the input voltage approaches the UVLO threshold and crosses 5V, the internal 5V VCC is regulated, and the external MOSFET is turned ON if the EN pin and the DIM pin are high. To use the EN and DIM functions of the MIC3205, a test point is provided for each of them. Ordering Information Part Number MIC3205YML EV Description Evaluation board with MIC3205YML device Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com December 2012 M9999-121312-A Micrel, Inc. MIC3205 Evaluation Board Evaluation Board Features EN Input The EN pin provides a logic level control of the output. The voltage must be 2.0V or higher to enable the current regulator. The output stage is gated by the DIM pin. When the EN pin is pulled low, the regulator goes into an off state and the supply current of the device is reduced to 1µA. A logic low pulls down the DRV pin, turning off the external MOSFET. Do not drive the EN pin above the supply voltage. Do not leave floating. R8 is provided for default “ON.” DIM Input The DIM pin provides logic level control for the brightness of the LED. The DIM pin can turn the LEDs on and off if EN is in an active-high state. The MIC3205YML EV board comes with a 100kΩ pull-up resistor installed (R5). R5 provides default 100% brightness. LED brightness can be controlled by varying the duty cycle, on the DIM input, from 1% to 99%. Do not leave floating. LED Current and RCS The CS and VINS pins provide the high-side current sense to set the LED current with an external sense resistor RCS. The MIC3205YML EV board comes with a 200mΩ RCS resistor installed as the default value, which corresponds to an LED current rating of 1A. The following equation gives the RCS value for required LED current: RCS = 200mV ILED MIC3205YML EV board comes with a 22µH inductor installed. Inductor L is given by: L= where: VLED is the total voltage drop of the LED string VIN is the input voltage RCS is the current sense resistor ILED is the average LED current VD is the freewheeling diode forward drop FSW is the operating switching frequency ∆VHYS is the hysteresis on the CS pin L is the inductor value Tables 1, 2, and 3 give reference inductor values for an operating frequency of 400 kHz, for a given LED current, freewheeling diode forward drop, and number of LEDs. By selecting ∆VHYS in the 55mV to 75mV range, we get the following inductor values: Eq. 1 For more information, please see the LED Current and RCS subsection in the Application Information section of the MIC3205 data sheet. Operating Frequency The operating switching frequency can be programmed by installing an external capacitor from the CTIMER pin to AGND. FSW 2.22 × 10 -4 = CT RCS (Ω) ILED (A) VIN (V) L (µH) ∆VHYS 0.56 0.35 5 22 64.1 0.56 0.35 12 68 57.7 0.28 0.7 5 10 70.5 0.28 0.7 12 33 59.4 0.2 1.0 5 6.8 72.6 0.2 1.0 12 22 62.4 0.1 2.0 5 3.6 68.5 0.1 2.0 12 10 68.6 (mV) Table 1. Inductor for FSW = 400 kHz, VD = 0.4V, 1 LED Eq. 2 The MIC3205YML EV board comes with a 470pF CT capacitor (C10) installed for default 400kHz frequency. For more information, please see the Frequency of Operation subsection in the Application Information section of the MIC3205 datasheet. Inductor The inductor value can be calculated after average LED current, operating frequency, and an appropriate hysteresis ∆VHYS value have been chosen. The December 2012 (VIN - ILED × RCS - VLED) × (VD + ILED × RCS + VLED) × RCS Eq. 3 ( VIN + VD) × ∆VHYS × FSW RCS (Ω) ILED (A) VIN (V) L (µH) ∆VHYS 0.56 0.35 24 150 55.8 0.56 0.35 36 220 56.8 0.28 0.7 24 68 61.6 0.28 0.7 36 100 62.5 0.2 1.0 24 47 62.4 0.2 1.0 36 68 64.3 0.1 2.0 24 22 66.6 0.1 2.0 36 33 66.2 (mV) Table 2. Inductor for FSW = 400 kHz, VD = 0.4V, 4 LEDs 2 M9999-121312-A Micrel, Inc. MIC3205 Evaluation Board RCS (Ω) ILED (A) VIN (V) L (µH) ∆VHYS 0.56 0.35 36 150 58.4 0.56 0.35 40 220 54.3 0.28 0.7 36 68 64.4 0.28 0.7 40 100 59.6 0.2 1.0 36 47 65.2 0.2 1.0 40 68 61.4 0.1 2.0 36 22 69.6 0.1 2.0 40 33 63.3 (mV) Table 3. Inductor for FSW = 400 kHz, VD = 0.4V, 8 LEDs The MIC3205YML EV board is set up for evaluation for one 1A LED. If more LEDs are required, the inductor value must be recalculated. If a different operating switching frequency is desired, the CT capacitor value must be recalculated. If LEDs with a current rating other than 1A need to be evaluated, the RCS value must be recalculated. The LED voltage drop depends on the manufacturer tolerance and number of LEDs. The LED current can be measured using an ammeter or current probe. The 4.7µF ceramic capacitor between the LED+ and LED– terminals is highly recommended, as it helps to reduce the current ripple through the LED. December 2012 3 M9999-121312-A Micrel, Inc. MIC3205 Evaluation Board Evaluation Board Performance (Typical Characteristics) Efficiency (ILED = 1A) vs. Input Voltage ILED Output Current vs. Temperature 100 1.03 90 ILED OUTPUT CURRENT (A) EFFICIENCY (%) 95 4 LED L = 47µH 85 6 LED L = 68µH 80 10 LED L = 33µH 1 LED L = 22µH 75 70 VIN = 12V VLED = 3.5V RCS = 0.2Ω 1.02 1.01 1.00 0.99 65 60 0.98 0 9 18 27 36 45 -50 -25 25 50 75 100 125 Switching Frequency vs. Temperature Normalized Switching Frequency vs. Input Voltage 2 530 ILED = 1A RCS = 0.2Ω 1 LED L = 22µH 1 6 LED L = 68µH 4 LED L = 47µH 0.5 VIN = 12V VLED = 3.5V L = 22µH CT = 470pF RCS = 0.2Ω 510 1.5 FREQUENCY (kHz) NORMALIZED FREQUENCY 0 TEMPERATURE (°C) INPUT VOLTAGE (V) 10 LED L = 33µH 490 470 450 0 0 9 18 27 36 430 45 -50 December 2012 -25 0 25 50 75 100 125 TEMPERATURE (°C) INPUT VOLTAGE (V) 4 M9999-121312-A Micrel, Inc. MIC3205 Evaluation Board Evaluation Board Performance (Functional Characteristics) December 2012 5 M9999-121312-A Micrel, Inc. MIC3205 Evaluation Board Evaluation Board Schematic December 2012 6 M9999-121312-A Micrel, Inc. MIC3205 Evaluation Board Bill of Materials Item Part Number 12105C475KAZ2A C1, C2,C3,C4,C11 C5 GRM32ER71H475KA88L C8 C7,C9 (2) 06036D475KAT2A AVX Murata CGA3E1X5R0J475K TDK 06035C102KAT2A AVX SK36-TP SK36 SK36-7-F 1µF/50V, Ceramic Capacitor, X7R, Size 0805 1 470pF/50V, Ceramic Capacitor, X7R, Size 0603 1 4.7µF/6.3V, Ceramic Capacitor, X5R, Size 0603 1 1nF/50V, Ceramic Capacitor, X7R, Size 0603 2 60V, 3A, SMC, Schottky Diode 1 22µH, 2.1A, 0.0591Ω, SMT, Power Inductor 1 MOSFET, N-CH, 60V, 12A, SO-8 1 0.2Ω Resistor, 1/2W, 1%, Size 1206 1 100kΩ Resistor, 1%, Size 0603 2 AVX Murata TDK GRM188R71H102KA01D 5 TDK C1608X7R1H471K GRM188R60J475KE19J 4.7µF/50V, Ceramic Capacitor, X7R, Size 1210 (3) Murata C1608X7R1H102K D1 Murata GRM21BR71H105KA12L GRM188R71H471KA01D Qty. AVX TDK 06035C471K4T2A Description (1) CGA6P3X7R1H475K CGA4J3X7R1H105K C10 Manufacturer Murata TDK (4) MCC Fairchild (5) Diodes, Inc. (6) L1 SLF10145T-220M1R9-PF M1 FDS5672 RCS CSR1206FKR200 R5, R8 CRCW0603100KFKEA R2, R3 CRCW060330R0FKEA Vishay Dale 30Ω Resistor, 1%, Size 0603 2 R1, R9 CRCW06032R00FKEA Vishay Dale 2Ω Resistor, 1%, Size 0603 2 R4 CRCW060310K0FKEA Vishay Dale 10kΩ Resistor, 1%, Size 0603 1 R6 CRCW060351R0FKEA Vishay Dale 51Ω Resistor, 1%, Size 0603 1 R7 CRCW06030000Z0EA Vishay Dale 0Ω Resistor, Size 0603 1 High-Brightness LED Driver Controller with Fixed-Frequency Hysteretic Control 1 U1 MIC3205YML TDK Fairchild Stackpole (7) Electronics, Inc. Vishay Dale (8) (9) Micrel, Inc. Notes: 1. AVX: www.avx.com. 2. Murata: www.murata.com. 3. TDK: www.tdk.com. 4. MCC: www.mccsemi.com. 5. Fairchild: www.fairchildsemi.com. 6. Diodes Inc.: www.diodes.com. 7. Stackpole Electronics: www.seielect.com. 8. Vishay Dale: www.vishay.com. 9. Micrel, Inc.: www.micrel.com. December 2012 7 M9999-121312-A Micrel, Inc. MIC3205 Evaluation Board PCB Layout Recommendations Top Layer Bottom Layer December 2012 8 M9999-121312-A Micrel, Inc. MIC3205 Evaluation Board MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB www.micrel.com Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. This information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry, specifications and descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual property rights is granted by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no liability whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2012 Micrel, Incorporated. December 2012 9 M9999-121312-A