MIC3263 Evaluation Board Six-Channel WLED Driver for Backlighting Applications with Flicker-Free Dimming Bringing the Power to Light™ General Description Getting Started This evaluation board (EVB) is designed for the MIC3263. The MIC3263 is a high-efficiency Pulse Width Modulation (PWM) boost switching regulator that is optimized for constant-current WLED driver backlighting applications. The MIC3263 drives six channels of up to ten low-power WLEDs per channel. Each channel is matched in current to within ±3% for constant brightness across the screen and can be programmed from 15mA to 30mA. The MIC3263 provides a very flexible dimming control scheme with high accuracy and noise immunity. The dimming frequency can be set to any value between 100Hz and 20kHz by an external resistor. The dimming ratio is determined by the duty-cycle of a dimming ratio control input signal and can be set to one of 16 levels with a minimum ratio of 1%. The LED dimming current is set by an external resistor to allow programming of LED current between 15mA and 30mA. The dimming ratio of the MIC3263 is fixed to 16 logarithmic levels to better match the sensitivity of the human eye. Each of the dimming levels has hysteresis to avoid skipping between levels resulting in Flicker-Free operation. The MIC3263 has a programmable PWM switching frequency from 400kHz to 1.8MHz to allow small inductor sizes. The 6V to 40V wide-input voltage range of MIC3263 allows direct operation from 6V or high cell count Li-Ion batteries commonly found in notebook computers. 1. Set the LED current of all six channels by one resistor RISET (noted as R9 on the EVB). Use 2kΩ for 30mA and 3kΩ for 20mA. Use the following equation to find RISET: Precautions The MIC3263 evaluation board operates as a boost converter, which requires the output voltage to be greater than the input voltage. Connect a PWM dimming signal to the DRC pin. The DRC pin needs an input signal to operate. Requirements 1. 2. 3. 4. 60 RISET = Ω ILED 2. Connect six strings of LEDs from LED out to LEDRTN. Each one of the six LED strings needs to connect to one of the LED RTN. The cathode end of each LED string connects to one of the six LED RTN pins. The anode end of all the LED strings connects to LED OUT (VOUT). The number of LEDs in each string should be from 4 to 10. 3. Connect 12V (or other input voltage) to VIN and GND. 4. Use a current probe to measure the load current and monitor the switch node with a scope to view the switching waveform 5. PWM Dimming: a. Connect a function generator to the dimming input (DRC pin) 0V to 5V at 100Hz to 40kHz. b. Adjust the duty-cycle of the function generator for PWM dimming. The MIC3263 converts the duty-cycle at the DRC to one of sixteen dimming ratios (DR) according to Table 1. c. Follow the power-on sequence to ensure all channels turn on. d. The EVB is set for 30mA LED current. For a different LED current, change R9 using the given equation. Voltage source capable of supplying 10W Load: Six LED strings Scope Function generator for PWM Dimming MLF and MicroLeadFrame are registered trademarks of Amkor Technology, Inc. Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com March 2010 M9999-032410-B Micrel, Inc. MIC3263 Evaluation Board Power-On Sequence OVP This is the over-voltage protection monitor. Also this is the feedback signal that connects to the error amplifier input. The output voltage that the OVP will trigger is set according to the following equation. Using the values for this example gives a max output voltage of: VIN needs to be present before PWM pulses are applied to the DRC pin. Some channels may not turn on if the power-on sequence is not followed. This may be the case if the circuits that monitor the IO pins see transients during the turn on-time and may interpret voltage spikes during turn-on as a fault, preventing that channel from turning on. When a channel is off, its IO pin is at high impedance. It is best to follow the sequence: 1. VIN 2. PWM dimming at DRC 3. Enable high VOVP = 2.4 × (R1+R2)/R1 = 38V Internal PWM Dimming The duty-cycle of the PWM pulse applied to the DRC input is converted to 16 log levels. This logarithmic dimming is a unique feature of the MIC3263 which better matches the sensitivity of the human eye compared to linear dimming. The DRC duty-cycle to DR duty-cycle conversion is shown in Table 2. MODE This selects the internal PWM dimming frequency range. When MODE is low, the PWM dimming frequency range is 100Hz to 2kHz and it selects low-frequency (LF) mode. When MODE is high, the PWMD frequency range is 1.5kHz to 20kHz and it selects high-frequency (HF) mode. N 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 DFS DFS stands for Dimming Frequency Select. The dimming frequency of the LEDs is different than the input dimming frequency at the DRC input. The MIC3263 uses an internal dimming frequency. This internal dimming frequency is programmable by an external resistor to ground RDFS (R8). When using internal dimming the range is determined by the MODE pin and the actual frequency is determined by RDFS. Connect a resistor-to-ground to select a dimming frequency. Use the following equations to determine the value for RDFS: RDFS(kΩ) = −20 × fDIM(kHz) + 432 (HF Mode) RDFS(kΩ) = −335 × fDIM(kHz) + 433 (LF Mode) For direct dimming control, connect DFS to VDD and use the MODE pin for the input dimming pulse. This method by passes the internal dimming control and allows for dimming control by the external PWM pulse. DRC Duty Cycle PWM Dimming Ratio (DR) DR = 10(N − 1) / 7 % % 0 6.25 12.5 18.75 25 31.25 37.5 43.75 50 56.25 62.5 68.75 75 81.25 87.5 93.75 0 1.0 1.4 1.9 2.7 3.7 5.2 7.2 10 14 19 27 37 52 72 100 Table 1. Dimming Ratio Ordering Information March 2010 2 Order Part Number Description MIC3263YML EV Boost Evaluation Board M9999-032410-B Micrel, Inc. MIC3263 Evaluation Board Figure 1. Schematic Diagram March 2010 3 M9999-032410-B Micrel, Inc. MIC3263 Evaluation Board Evaluation Board Design Specifications Parameter Minimum Typical Maximum 6V 6 40V 18-25 38V VIN Output Voltage Number of LEDs/Channel 4 LED Current 8 10 15mA Power Out 30mA 0 5W Switching Frequency (FIXED) 400kHz 1MHz 1.8MHz PWM Dim Frequency 100Hz 300Hz 20kHz Efficiency 7W 90% Line Regulation <±3% Load Regulation <±3% Ambient Temperature –40°C +25°C +85°C Table 1. Evaluation Board Design Specifications March 2010 4 M9999-032410-B Micrel, Inc. MIC3263 Evaluation Board Bill of Materials Item Part Number Manufacturer C1 C2, C6 C3, C8 C4 C5 C7 Description Qty. OPEN 0603ZC222KAT2A AVX(1) C1608X7R1H222K TDK(2) GRM188R71H222K muRata C5750X7R1H106M TDK(2) 22205C106KAZ2A AVX(1) GRM21BR71A106KE51L muRata(3) 0805ZD106KAT2A AVX(1) 0603YC104KAT2A AVX(1) C1608X7R1C104K TDK(2) muRata 0603ZD225KAT2A AVX(1) GRM188R61A225KE34D muRata(3) D1 L1 2 10μF, 50V, X7R, 2220 2 10μF, 10V, X7R, 0805 1 0.1μF, 16V, X7R, 0603 1 2.2μF, 10V, X5R, 0603 1 Schottky 3A, 40V (SMA) 1 22μH, 2.6A 1 (3) GRM188R71C104K C1608X5R1A225K 2200pF, 10V, X7R, 0603 (3) TDK (2) SK34A MCC(4) B349LA-13 Diode, Inc. (5) DO3316P-223ML Coilcraft(6) (7) R1 CRCW0603150KFKEA Vishay Dale 150k 2 R2 CRCW060310K0FKEA Vishay Dale(7) 10k 1 (7) 110k (RSLP) 1 (7) R3 CRCW0603110KKFKEA Vishay Dale R4 CRCW060315K0FKEA Vishay Dale 15.0k (RCOMP) 1 R5 CRCW0603200KFKEA Vishay Dale(7) 200k 1 CRCW060340K2FKEA (7) 4.02k (7) 100k 1 (7) R6 R7 CRCW0603100KFKEA Vishay Dale Vishay Dale R8 CRCW060326K7FKEA Vishay Dale 97.6k 1 R9 CRCW06032K00FKEA Vishay Dale(7) 2k 1 Six-Channel WLED Driver for Backlighting Applications 1 U1 MIC3263YML Micrel, Inc. (8) Notes: 1. AVX: www.avx.com. 2. TDK: www.tdk.com. 3. Murata Tel: www.murata.com. 4. MCC: www.mccsemi.com. 5. Diode, Inc.: www.diodes.com. 6. Coilcraft: www.coilcraft.com. 7. Vishay: www.vishay.com. 8. Micrel, Inc.: www.micrel.com. March 2010 5 M9999-032410-B Micrel, Inc. MIC3263 Evaluation Board Evaluation Board PCB Layout March 2010 6 M9999-032410-B Micrel, Inc. MIC3263 Evaluation Board Package Information 24-Pin 4mm x 4mm (MLF®) March 2010 7 M9999-032410-B Micrel, Inc. MIC3263 Evaluation Board Recommended Land Pattern 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. © 2010 Micrel, Incorporated. March 2010 8 M9999-032410-B