MIC3232 Evaluation Board High Voltage Boost HBLED Driver with PWM Dimming Control Bringing the Power to Light™ General Description The MIC3232 is a constant current boost switching controller specifically designed to power one or more strings of high power LEDs. The MIC3232 has an input voltage range from 6V to 45V and is ideal for a variety of applications. The MIC3232 is the fixed 400kHz version of the MIC3230, in a 10-pin MSOP package. The MIC3232 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 MIC3232 is 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 1A. 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. 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 How it works The MIC3232 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 MIC3232 is off, the input is connected to the output through the inductor (L1) and diode (D1). The input voltage (VIN) is effectively applied across the LEDs and will turn on if VIN is greater than the sum of the forward voltage drops across the LED string. 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 to 0.4A. The evaluation board is currently set to this output current value. ILED = VREF R7 Where VREF = 0.25 PWM Dimming A PWM signal applied to the PWMD pin turns the current to the LEDs on and off. When PWMD is high, the MIC3232 is enabled and the boost converter regulates the LED current by keeping the voltage drop across the R7 resistor constant. When PWMD is low the converter turns off and the LED current discharges the output capacitors and the LED current stops. Ordering Information Part Number Description MIC3232YMM EV Evaluation board for the MIC3232YML IC 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. 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. MIC3232 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 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 MIC3232 features current limit sensing. Current limit is set through the external resistor, R6, 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 the R9 resistor, according to equation: OVP = 1.245 V = (R8 + R9) On the evaluation board, these values have been set to: R9=2kΩ and R8=100kΩ and VO,MAX = 64V. C3 1000pF 100V R4 1/2 W L1 47µH J1 VIN C1 4.7uF 50V R1 J3 EN J4 PWMD Dim VIN 2 EN OVP 7 3 PWMD DRV 9 IS 6 IADJ 5 C5 10uF 6.3V COMP VDD Q1 SI7148DP C6 2.2uF 100V R5 C7 2.2uF 100V R10 OPEN R9 Vfb=0.25V R7 R6 1/4W 1/2 W PGND C4 10nF R8 1 10 J6 +Vout to LED D1 SS5P10-E3 MIC3232YMM MSOP-10 4 R3 J2 GND (R9 × VO,MAX ) 8 J7 LED RTN Figure 1. Schematic Diagram July 2009 2 M9999-071609-A (408) 944-0800 Micrel, Inc. MIC3232 Evaluation Board Evaluation Board Design Specifications MIN TYP MAX VIN 6V 12-24 45V Output Voltage Vin 12-24 Series LEDs 90V* LED Current 0 0.2-.5 0.70A Power Out 0 20W 70W Efficiency 90% Switching Frequency 100kHz 400kHz 1MHz PWM Dim Frequency 0 300Hz 500Hz 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 (ohms) I_LED 5 50mA 2 125mA 1 250mA 0.62 404mA 0.5 500mA 0.4 625mA .35 0.7A Table 2. LED current selection July 2009 3 M9999-071609-A (408) 944-0800 Micrel, Inc. MIC3232 Evaluation Board Bill of Materials Item Part number U1 MIC3232-YMM Q1 Si7148DP-T1 D1 SS5P10-E3 L1 MSD1278-473ML Coilcraft 47µH, rate 5.2A inductor 1 C1 GRM32ER71H475KA88L Murata 4.7µF/50V, 1210, Ceramic capacitor 1 C5 GRM21BR61A106KE19L Murata 10uF/10V, 0805, ceramic capacitor 1 LMK212BJ106KD-T C0805C106K8PACTU C3 VJ0805Y102KXBAT. OR GRM2195C2A102JA01B. Manufacturer Micrel.Inc Part Description Quant Constant Current Boost control for Hi Power LED 1 Vishay Siliconix. N Channel 75V MOSFET 1 Vishay corp 5A, 100V schottky diode 1 Taiyo Yuden OR Kemet OR Vishay Vitramon 1nF/100V,0805, Ceramic capacitor 1 Murata C2012X7R2A102K TDK C6,C7 C4532X7R2A225K TDK 2.2µF/100V,1812, Ceramic capacitor OR GRM32ER72A225KA35L. Murata 2.2uF/100V, 2220, Ceramic capacitor C4 VJ0603Y103KXBAT. OR GRM188R71H103KA01D. R1,R8 CRCW0603100KFKEA. Vishay Dale 100kΩ, 0603, 1% 2 R3 CRCW06030000FKEA. Vishay Dale 0Ω, 0603 1 R4 CRCW20102R00FKEF Vishay Dale 2Ω, 1/2W, 2010 1 R9 CRCW06032K00FKEA. Vishay Dale 2kΩ, 0805 1 R5 CRCW12064990FKEA. Vishay Dale 499Ω, 1206 1 R6 WSL2010-R0750-FKEA Vishay Dale 0.075Ω, 1/2W, 1812 1 R7 CRCW1206R620JNTALR. Vishay Dale 0.620Ω, 1/4W, 1206 1 Open 1 Vishay Vitramon 10nF/50V, 0603, Ceramic capacitor Murata R10 2 1 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. MIC3232 Evaluation Board Top Layer July 2009 5 M9999-071609-A (408) 944-0800 Micrel, Inc. MIC3232 Evaluation Board Bottom Layer 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 6 M9999-071609-A (408) 944-0800