MIC2298 Evaluation Board 3.5A ISWMIN,1MHz, High Power LED Driver 3 Preset LED Current Setting General Description This board enables the evaluation of the MIC2298, a fully integrated 7W net output minimum High Power white LED driver. The board includes components necessary to set the LED current to 20%, 50% and 100% of the nominal LED current (1A). The external inputs also allow the LED current to be programmed either with additional resistors or voltages on the DIM or BRT pins. Also the enable pin can be driven to force the part into low IQ mode. The MIC2298, 1MHz, Integrated Step up current regulator, allows the use of small and very few external components to create a compact boosted supply up to 30V. The evaluation board has been configured with three fixed current settings chosen using JP1 and all externally programmable inputs are accessible via board pins. Requirements The MIC2298 evaluation board requires an input power source that is able to deliver at least 5A over the desired input voltage range. For the load, an electronic load (ELoad) capable of constant voltage testing is required or a high power LED mounted on a fan cooled heat sink. Note that stability measurements must be carried out on an LED load as E-Loads do not have the same dynamic characteristics of a high power LED. Precautions The evaluation board does not have reverse polarity protection. Applying a negative voltage to the VIN (J1) terminal may damage the device. The load current is only regulated if connected between VOUT and FB terminals, the GND terminal close to the VOUT terminal is provided for voltage measurements only. The MIC2298 has a maximum input voltage rating of 10V therefore, the supply voltage should never exceed this value. Getting Started 1. Connect the input supply to the input terminals. Take note of the polarity to prevent damage. An ammeter can be used in-line with the VIN terminal to measure input current. The Input voltage should be measured at the input terminals to account for any drops in test leads and amp meter. 2. Ensuring the jumper JP1 is at the top position (50% load), connect the load to the output terminals: +VO connects to the positive E-Load input or Anode of the test LED, FB connects to the negative E-Load input or the Cathode of the test LED. A low impedance ammeter can be connected inline with the +VO terminal for current measurements. The output voltage should be measured between the evaluation board terminals +VO and GND (to measure converter efficiency) or +VO and FB (to measure the voltage of the LED load). 3. Connect a normally closed (NC) momentary switch between enable and GND or alternatively, connect a pulse generator set to output a 2V pulse of 300ms every 3s to the enable input. 4. Switch on the E-Load (if using), pulse generator and then the input supply. Measurements can now be taken of efficiency, switching waveform and output current regulation. When testing 1A load (JP1 open), ensure that these are only pulse tests to prevent damage to the LED. LED manufacturers recommend <10% duty cycle and 3s period. Ordering Information Part Number Description MIC2298-15YML EV Evaluation Board with MIC229815YML 15V OVP 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 June 2008 M9999-062508-B Micrel, Inc. MIC2298 Evaluation Board The external pins can be driven to set any current between the minimum and maximum values. See Table 1 below. The nominal current setting can be reduced by choosing a larger value for R1 (current sense resistor). The 100% current level can be set by using the following equation: ILED100% = 0.2V/R1 The values in the table will scale with the nominal 100% current setting. So for example, if the 100% current is set to 500mA, 0Ω on BRT will set LED current to 100mA, 50kΩ to 250mA etc. Evaluation Board DIM Voltage Board Description By default, the board is set to give 500mA nominal current into two series connected Power LEDs (JP1 at 50% position). If the load is not present, the over voltage protection (OVP) will limit VOUT to prevent damage to the MIC2298. JP1 can be removed to set the load current higher to 1A (Flash) or moved to 20% to set a lower 200mA current (Torch). Care should be taken as removing the jumper will result in the maximum LED drive current of 1A. 0V to 200mV LED Current BRT = Open 40mA to 1A BRT = GND 0 to 200mA BRT Voltage 0V to 1V LED Current DIM = 200mV 200mA to 1A BRT Resistance 0Ω to 100kΩ LED Current DIM = 200mV 200mA to 1A Table 1. MIC2298 Dimming Methods Board Performance High Power White LED Driver VIN = 3.6V; Efficiency ~ 85% at full load (Peak > 87%) 50 40 Bode Plot 4.7µH (1A LED Load) 180 144 50 40 30 108 30 108 20 10 72 36 20 10 72 36 0 -10 -36 0 -10 -72 -20 -108 -144 -30 -40 -20 -30 -40 -50 1 Gain (3VIN) Gain (4.2VIN) Phase (3VIN) Phase (4.2VIN) 10 100 FREQUENCY (kHz) -180 1000 -50 1 Stability 4.7µH Inductor June 2007 Bode Plot 2.2µH (1A LED Load) 180 144 -36 Gain (3VIN) Gain (4.2VIN) Phase (3VIN) Phase (4.2VIN) 10 100 FREQUENCY (kHz) -72 -108 -144 -180 1000 Stability 2.2µH Inductor 2 M9999-062508-B Micrel, Inc. MIC2298 Evaluation Board 1100 1000 900 800 700 600 500 400 300 200 100 0 0 LED Current vs. DIM Voltage 1100 1000 900 800 700 600 500 400 300 200 100 0 0 40 80 120 160 200 DIM VOLTAGE (mV) LED Current vs. RBRT VIN = 3.6V 20 40 60 80 100 120 140 LED Current Programming (VDIM) LED Current Programming (BRT) Switching Waveforms (BRT – GND) PWM Programming 250 LED Current vs. DC (on EN Pin) 1200 LED Current vs. DC (on BRT Pin) 1000 200 800 150 600 100 400 50 0 0 200 20 40 60 80 Duty Cycle (%) 0 0 100 LED Current Programming (100Hz PWM on Enable) June 2007 5 10 15 20 25 Duty Cycle (%) 30 35 LED Current Programming (1kHz PWM on BRT) 3 M9999-062508-B Micrel, Inc. MIC2298 Evaluation Board Schematic Bill of Materials Item Part Number C1 C1608X5R1A225M C2 VJ0603Y104KXAAT Manufacturer TDK (1) Vishay(2) (1) Description Qty 2.2µF/10V, 0805 Ceramic Capacitor 1 0.1µF/50V, 0603 Ceramic Capacitor 1 100pF/50V, 0603 Ceramic Capacitor 1 C3 C1608C0G1H101J TDK C4 C1608X5R1H333K TDK(1) 33nF/16V, 0603 Ceramic Capacitor 1 C5 C2012X5R1C475K TDK(1) 4.7µF/16V (X7R or X5R), 0805 Ceramic Capacitor 1 100µF/16V, TPSD size Tantalum Capacitor 1 2A, 20V Schottky Diode 1 C6 TPSD107M016R0100 (3) AVX Diodes, Inc. (4) D1 DFLS220L L1 IHLP2525AHER4R7M01 Vishay(2) 4.7µH, 8A, 7x7x1.2mm Inductor 1 R1 L0805M0R20FN Vishay(2) 200mΩ, 0.2W, 0805 Metal film, 200mW Resistor 1 (2) R2 CRCW0603620RFKTA Vishay 620Ω, 0603 Resistor 1 R3 CRCW060349K9FKEA Vishay(2) 49.9KΩ, 0603 Resistor 1 R4 CRCW06036K98FKEA Vishay(2) 6.98KΩ, 0603 Resistor 1 JP1 3 pin Header Header for Current Setting 1 3.5A ISWMIN, 1MHz High Power LED Driver 1 U1 MIC2298-15YML Micrel (5) Notes: 1. TDK: www.tdk.com 2. Vishay: www.vishay.com 3. AVX: www.avx.com 4. Diodes, Inc.: www.diodes.com 5. Micrel, Inc: www.micrel.com June 2007 4 M9999-062508-B Micrel, Inc. MIC2298 Evaluation Board PCB Layout Recommendations Top Layer Bottom Layer June 2007 5 M9999-062508-B Micrel, Inc. MIC2298 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. © 2007 Micrel, Incorporated. June 2007 6 M9999-062508-B