MIC3230/1 Evaluation Board High Voltage Boost HBLED Driver with PWM Dimming Control Bringing the Power to Light™ General Description The MIC3230/1 are constant current boost switching controllers specifically designed to power one or more strings of high power LEDs. The MIC3230/1 have an input voltage range from 6V to 45V and are ideal for a variety of applications. The MIC3230/1 utilizes an external power device which offers a cost conscious solution for driving high power LED applications. Power consumption has been minimized through the implementation of a 250mV feedback voltage reference providing an accuracy of ±3%. The MIC3230/1 are dimmable via a PWM input signal and also features an enable pin for low power shutdown. The LED current is regulated by keeping the voltage drop across the current sense resistor (R7) constant. The LED current can be set by selecting the value of R7. In this version of the eval board, the output current is limited to 750mA. Multiple MIC3230 ICs can be synchronized to a common operating frequency by connecting the ICs together through the SYNC pin. This feature is only good on the MIC3230. The clocks of these synchronized devices can be used together which help reduce noise and errors in a system. The MIC3231 offers a dither feature to assist in the reduction of EMI. This is particularly useful in sensitive EMI applications, and provides for a reduction in emissions by approximately 10dB. Table 1 provides a summary of the eval board specifications. The evaluation board schematic is shown in Figure 1 and the parts list is shown in the Bill of Materials table. The switching frequency is determined by the selection of R1. The chart in Figure 2 can be used to select the desired frequency. The board is set at approximately 500kHz. Requirements 1. Voltage source capable of supplying 50 Watts 2. Load: LED, resistive or electronic load 3. Scope 4. Voltage meter 5. (Optional) Function generator for PWM Dimming Precautions The evaluation board does not have input reverse polarity protection. Applying a negative voltage at the VIN terminal may damage the board. When the controller is off there is a current path through the inductor and the flyback diode to the output. No current limit exists for this current path so care must be taken not to short circuit the output. How it works The MIC3230/1 evaluation board is set to operate as a boost converter, which requires the output voltage to be greater than the input voltage. It is important to have the series LED forward voltage drops be greater than the input voltage because when the converter is off the input is connected to the output through the inductor (L1) and diode (D1). VIN is effectively applied across the LEDs and will turn on if the series sum of their forward voltage drop is not greater than VIN. For 100% duty cycle, simply pull PWMD high or leave open. For a different LED current change R7 using the following equation. When R7 is 0.62Ω, the LED current is equal to 0.4A. The evaluation board is currently set to this output current value. ILED = VREF R7 Where VREF = 0.25V PWM Dimming A PWM signal applied to the PWMD pin turns the current to the load LEDs on and off. When PWMD is high the MIC3230/1 is enabled and the boost converter regulates the LED current by keeping the voltage drop across R7 constant. When PWMD is low the converter turns off and the LED current discharges the output caps and LED current stops. Ordering Information Part Number Description MIC3230ML BOOST EV Boost evaluation board for the MIC3230YML IC MIC3231ML BOOST EV Boost evaluation board for the MIC3231YML IC Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com July 2009 M9999-071609-A (408) 944-0800 Micrel, Inc. MIC3230/1 Evaluation Board Quick-Start Guide 1. Connect a load (LED series string or resistive load) between VOUT and LED RTN (this is not the same as ground). 2. Connect 12V (or other input voltage) to VIN and GND. 3. Use a current probe to measure the load current. and Monitor the Switch node with a scope to view the switch waveform 4. PWM Dimming: a. For no PWM dimming, leave the PWMD terminal open b. For PWM DIMMING connect a function generator to the PWM DIM input and GND (not LED RTN). Set the output at 0-5V square wave pulse at 300Hz. Make sure the pulse goes all the way to 0V. RSET – Current Limit Sensing The MIC3230/1 features current limit sensing. Current limit is set by an external resistor by the following equation: IS=0.5V = R6×IQ1 Where, IQ1 is the peak FET current that will trigger the current limit, the Default setting for the evaluation board is R6 = 75mΩ with the current limit set at 6.7A. OVP – Setting the over voltage protection OVP is set with R9 according to this equation; OVP = 1.245 V = L1 4.7µH D1 SS5P10-E3 U1 MI C3230-YML C2 4.7µF 50V C3 100pF /100V 1 J6 1 +V OUT LED R8 1 VIN OVP 9 2 EN DRV 11 8 7 6 5 R1 100k C1 4.7µF 50V (R8 + R9) On the evaluation board, these values have been set to: R9 = 2kΩ and R8 = 100kΩ and VO,MAX = 64V. R4 1 /2W J1 +VIN 1 (R9 × VO,MAX ) R5 J4 PWM Dim 1 3 PWMD J5 SYNCH 1 7 SYNC 6 FS 4 COMP IADJ 5 VDD GND 10 R2 IS C7 2.2µF 100V R10 TBD/OPEN R6 0.075 1 /2W VFB=0.25V R9 J7 1 LED RTN R7 12 C4 10nF C6 2.2µF 100V 8 R3 J2 GND 1 Q1 SI7148DP 4 1 2 3 J3 EN 1 EPAD C5 10uF/10V Figure 1. Schematic Diagram July 2009 2 M9999-071609-A (408) 944-0800 Micrel, Inc. MIC3230/1 Evaluation Board Evaluation Board Design Specifications MIN TYP MAX VIN 6V 12-24 45V Output Voltage Vin 12-20 Series LEDs 70V LED Current 0 0.2-0.5 1A Power Out 0 20W 70W Switching Frequency 100kHz 400kHz 1MHz PWM Dim Frequency 0 300Hz 500Hz Efficiency 90% Line Regulation <3% Load Regulation <3% Ambient Temperature –40°C +25°C +85°C *Evaluation Board parts are rated to 75V Table 1. Evaluation Board Design Specifications LED current selection R7 (Ω) I_LED 5 50mA 2 125mA 1 250mA 0.62 404mA 0.5 500mA 0.4 625mA .25 1A Table 2. LED current selection Figure 2. Frequency selection July 2009 3 M9999-071609-A (408) 944-0800 Micrel, Inc. MIC3230/1 Evaluation Board Bill of Materials Item C1, C2 Part Number GRM32ER71H475KA88L VJ0805Y102KXBAT C3 C4 C5 C6, C7 GRM2195C2A102JA01B Manufacturer Description Murata Qty. 4.7µF/50V,1210, Ceramic capacitor 2 1nF/100V, 0805, Ceramic capacitor 1 10nF/50V, 0603, Ceramic capacitor 1 10µF/10V, 0805 , Ceramic capacitor 1 Vishay Vitramon Murata C2012X7R2A102K TDK VJ0603Y103KXBAT Vishay Vitramon GRM188R71H103KA01D GRM21BR61A106KE19L C0805C106K8PACTU LMK212BJ106KD-T Murata Murata Kemet Taiyo Yuden GRM32ER72A225KA35L Murata 2.2µF/100V, 1210, Ceramic capacitor TDK 2.2µF/100V, 1812, Ceramic capacitor C4352X7R2A225K 2 R1,R8 CRCW0603100KFKEA Vishay Dale 100kΩ, 0603, 1% 2 R2 CRCW060321K5FKEA Vishay Dale 21.5kΩ, 0603 1 R3 CRCW06030000FKEA Vishay Dale 0Ω, 0603 1 R4 CRCW2010R00FKEF Vishay Dale 2Ω, 1/2W, 2010 1 R5 CRCW06034990FKEA Vishay Dale 499Ω, 1/4W, 0603 1 R6 WSL2010-R0750-FKEA Vishay Dale 0.075Ω, 1/2W, 1812 1 R7 CRCW1206R620JNTALR Vishay Dale 0.620Ω, 1/4W, 1206 1 R9 CRCW06032K00FKEA Vishay Dale 2kΩ, 0603 1 L1 MSD1278-473ML Coilcraft 47µH, rate 5.2A inductor 1 D1 SS5P10-E3 Vishay Corp. 5A, 100V schottky diode 1 Q1 Si7148DP-T1 Vishay Siliconix N-Channel 75V MOSFET 1 Micrel, Inc Boost controller for High Power LEDs 2 U1 MIC3230-YML MIC3231-YML Notes: 1. DigiKey: www.digikey.com 2. Murata: www.murata.com 3. Vishay: www.vishay.com 4. AVX: www.avx.com 5. TDK: www.tdk.com 6. Diodes, Inc.: www.diodes.com 7. Sumida: www.sumida.com 8. International Rectifier: www.irf.com 9. Micrel, Inc: www.micrel.com July 2009 4 M9999-071609-A (408) 944-0800 Micrel, Inc. MIC3230/1 Evaluation Board Top Layer July 2009 5 M9999-071609-A (408) 944-0800 Micrel, Inc. MIC3230/1 Evaluation Board Bottom Layer July 2009 6 M9999-071609-A (408) 944-0800 Micrel, Inc. MIC3230/1 Evaluation Board MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. 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. © 2009 Micrel, Incorporated. July 2009 7 M9999-071609-A (408) 944-0800