MIC3202/MIC3202-1 Evaluation Board High-Brightness LED Driver with Integrated MOSFET and High-Side Current Sense General Description Getting Started The MIC3202/MIC3202-1 is a hysteretic step-down, constant-current, High-Brightness LED (HB LED) driver. It provides an ideal solution for interior/exterior lighting, architectural and ambient lighting, LED bulbs, and other general illumination applications. This board enables the evaluation of the MIC3202/MIC3202-1 for 1A LED current. The board is optimized for ease of testing, with all the components on a single side. The device operates from a 6V to 37V input voltage range, and includes an integrated 1.0A MOSFET. When the input voltage approaches and crosses UVLO threshold, the internal 5V VCC is regulated and the integrated MOSFET is turned on if EN pin and DIM pin are high. The inductor current builds up linearly. When the CS pin voltage hits the VCS(MAX) with respect to VIN, the internal MOSFET is turned off and the Schottky diode takes over and returns the current to VIN. Then the current through inductor and LEDs starts decreasing. When CS pin hits VCS(MIN), the internal MOSFET is turned on and the cycle repeats. Since the control scheme does not need loop compensation, it makes for a very simple design and avoids problems of instability. Datasheets and support documentation can be found on Micrel’s web site at: www.micrel.com. Requirements This board needs a single-bench power source adjustable over the input voltage of 6V < VIN < 37V that can provide at least 1A of current. The loads can either be active (electronic load in CV mode) 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, ensure that the correct polarity is observed. In the line transient condition, such as hot plug-in, an electrolytic capacitor may be required at the VIN and GND terminals in order to prevent IC damage from a surge voltage. 1. Connect VIN supply to the input VIN and GND terminals. With the output of this supply disabled, set the supply voltage to the desired input test voltage (6V < VIN < 37V). This supply voltage should be monitored at the test boards input terminals to allow voltage drops in the test cables (and ammeter if used) to be accounted for. An ammeter can be added inline with the +VIN input terminal to accurately measure input current. 2. Connect the LEDs to the output terminals between LED+ and LED−. This LED voltage drop depends on manufacturer tolerance and number of LEDs. The LED current can be measured using an ammeter or current probe. A 4.7µF ceramic capacitor helps to reduce the current ripple through the LED. The LED current is set to 1A by a 200mΩ current-sense resistor (RCS). 3. Enable the input supply. By default, the IC is enabled when the input voltage crosses the VIN threshold (4V) and the internal VCC regulator and internal MOSFET are turned on with the EN and DIM pins are high. To use the EN and DIM functions of the MIC3202/MIC3202-1, a test point is provided for each of them. Ordering Information Part Number Description MIC3202YME EV MIC3202YME Evaluation Board Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com October 2010 M9999-102810 Micrel, Inc. MIC3202/MIC3202-1 Evaluation Board Other Features EN Input The EN pin provides a logic level control of the output and the voltage has to 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 to off-state and the supply current of the device is reduced to below 1µA. Do not drive the EN pin above the supply voltage. DIM Input The DIM pin provides a logic level control for brightness of the LED. A PWM input can be used to control the brightness of LED. DIM high enables the output and its voltage has to be 2.0V or higher. DIM low disables the output, regardless of EN high-state. Current-Sense Input The CS pin provides the high-side current sense to set the LED current with an external sense resistor. A sense resistor RCS is placed between VIN and LED+ terminals. The current through LED is sensed by the sense resistor (RCS). The sensed voltage is fed back to the MIC3202 to regulate the LED current RCS is given by: 1 VCS(MAX) + VCS(MIN) x( ) 2 ILED Bookmark not defined. RCS = Error! Frequency of Operation To calculate the frequency spread across input supply: FSW = ΔIL = (VD +ILED×RCS + VLED) ×(VIN - ILED×RCS - VLED) L × ΔIL ×(VD + VIN) VCS(MAX ) - VCS(MIN) RCS where: VD is Schottky diode forward drop VLED is total LEDs voltage drop VIN is input voltage ILED is average LED current According to the above equation, choose the inductor to make the operating frequency no higher than 1MHz. Refer to the datasheet Application Information for more information on components selection guidelines. Frequency Dithering The MIC3202 is designed to modulate the VCS(MAX) with amplitude ±6mV by a pseudo random generator to generate the ±12% of the switching frequency dithering. This spreads the frequency spectrum over a wider range and reduce the EMI noise peaks. The MIC3202-1 is non-dithering version of the MIC3202. ILED is LED current required to set. RCS (Ω) ILED (A) I2R (W) Size (SMD) 1.33 0.15 0.03 0603 0.56 0.35 0.07 0805 0.4 0.5 0.1 0805 0.28 0.7 0.137 0805 0.2 1.0 0.2 1206 For VCS(MAX) and VCS(MIN) refers to the Electrical Characteristics table. October 2010 2 M9999-102810 Micrel, Inc. MIC3202/MIC3202-1 Evaluation Board Evaluation Board Performance October 2010 3 M9999-102810 Micrel, Inc. MIC3202/MIC3202-1 Evaluation Board Evaluation Board Schematic Notes: 1. If bulk capacitor on input rail is away (4 inches or more) from the MIC3202/MIC3202-1, install the 100µF bulk capacitor near VIN. 2. Source impedance should be as low as 10mΩ. October 2010 4 M9999-102810 Micrel, Inc. MIC3202/MIC3202-1 Evaluation Board Bill of Materials Item C1, C2, C8 Part Number 12105C475KAZ2A GRM32ER71H475KA88L 08053D105KAT2A C3, C9 C4, C7 GRM21BR71E105KA99L D1 Murata(2) AVX(1) Murata AVX(1) GRM188R71H104KA93D (2) Murata 4.7µF/50V, Ceramic Capacitor, X7R, Size 1210 2 1µF/25V, Ceramic Capacitor, X5R, Size 0805 1 1µF/25V, Ceramic Capacitor, X7R, Size 0805 1 270pF/50V, Ceramic Capacitor NPO, Size 0603 2 0.1µF/50V, Ceramic Capacitor, X7R, Size 0603 2 60V, 2A, SMA, Schottky Diode 1 30V, 200mA, Schottky diode, SOD-323 2 47µH, 1.4A, SMT, Power Inductor 1 0.2Ω Resistor, 1/2W, 1%, Size 1206 1 AVX(1) Murata(2) (3) C1608X7R1H104K TDK SS24-TP MCC(4) B0530WS-TP Qty. (2) 06035C271KAT2A SS24 D2, D3 AVX TDK(3) GRM188R71H271KA01D Description (1) C2012X7R1E105K 06035C104MAT C5, C6 Manufacturer Fairchild(5) MCC(4) L1 SLF10145T-470M1R4 R1 CSR 1/2 0.2 1% I R2, R3 CRCW06031003FKEA Vishay(8) 100kΩ Resistor, 1%, Size 0603 2 R4 CRCW08052R20FKEA Vishay(8) 2.2Ω Resistor, 1%, Size 0805 1 CRCW080510R0FKEA (8) 10Ω Resistor, 1%, Size 0805 1 (8) 10kΩ Resistor, 1%, Size 0603 1 (8) R5 R6 CRCW060310K0FKEA TDK (3) Stackpole Electronics, (7) Inc Vishay Vishay R7, R8 CRCW06030000FKEA Vishay 0Ω Resistor, 1%, Size 0603 2 R9 CRCW060349R9FKEA Vishay(8) 49.9Ω Resistor, 1%, Size 0603 1 POT 100kΩ 3/8" SQ CERM SL ST 1 Bourns (9) RV1 3386P-1-104TLF U1 MIC3202YME Micrel, Inc.(10) High Brightness LED Driver with High-Side Current Sense 1 U2 MIC1557YM5 Micrel, Inc.(10) RC Time/Oscillator (SOT-23-5) 1 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: www.vishay.com. 9. Bourns Inc : www.bourns.com. 10. Micrel, Inc.: www.micrel.com. October 2010 5 M9999-102810 Micrel, Inc. MIC3202/MIC3202-1 Evaluation Board PCB Layout Recommendations Top Assembly Top Layer October 2010 6 M9999-102810 Micrel, Inc. MIC3202/MIC3202-1 Evaluation Board PCB Layout Recommendations (Continued) 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 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. © 2010 Micrel, Incorporated. October 2010 7 M9999-102810