MIC4802 High Efficiency 800mA Single Channel Linear WLED Driver with Ultra Fast PWM™ Control General Description Features The MIC4802 is a high efficiency White LED (WLED) driver designed to drive a single LED up to 800mA. The MIC4802 constant current driver is designed to drive high power LED’s in various lighting applications. The MIC4802 provides the highest possible efficiency as this architecture has no switching losses present in traditional charge pumps or inductive boost circuits. It features a typical dropout of 280mV at 800mA. This allows the LEDs to be driven directly from the voltage source eliminating switching noise/losses present with the use of boost circuitry. The high accuracy (±1% Typical) current regulated WLED channel ensures uniform display illumination under all conditions. The brightness is controlled through an Ultra Fast PWM™ Control interface operating down to less than 1% duty cycle. The MIC4802 is available in the 8-pin SOIC Epad package with a junction temperature range of -40°C to +125°C. Datasheets and support documentation can be found on Micrel’s web site at: www.micrel.com. • • • • • • High Efficiency (no Voltage Boost losses) Ultra Fast PWM™ control (200Hz to 500kHz) Input voltage range: 3.0V to 5.5V Dropout of 280mV at 800mA Programmable LED current with external resistor Current accuracy of ±1% typical Applications • Bill board displays • Marquee displays • Instrument displays • Architectural lighting ____________________________________________________________________________________________________________ Typical Application High Current Lighting Schematic Ultra Fast PWM is a trademark of Micrel, 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 January 2011 M9999-013111-B Micrel Inc. MIC4802 Ordering Information Part Number Temperature Range Package MIC4802YME –40°C to +125°C 8-Pin EPAD SOIC Pin Configuration 8-Pin Epad SOIC (ME) (Top View) Pin Description Pin Number Pin Name 1 VIN Voltage Input. Connect at least 2.2µF ceramic capacitor between VIN and GND. 2 EN Enable LED drivers. This pin can be used as a PWM input for dimming of WLEDs. Do not leave floating. 3 RSET An internal 1.27V reference sets the nominal maximum WLED current. Example, apply a 6.19kΩ resistor between RSET and GND to set LED current to 830mA at 100% duty cycle. 4 GND Ground. 5 D1 LED1 driver input. Connect LED anode to VIN and cathode to this pin. All D1 pins must be connected to the LED. 6 D1 LED1 driver input. Connect LED anode to VIN and cathode to this pin. All D1 pins must be connected to the LED. 7 D1 LED1 driver input. Connect LED anode to VIN and cathode to this pin. All D1 pins must be connected to the LED. 8 D1 LED1 driver input. Connect LED anode to VIN and cathode to this pin. All D1 pins must be connected to the LED. EPAD HS PAD January 2011 Pin Function Heat sink pad. Not internally connected. Connect to ground. 2 M9999-013111-B Micrel Inc. MIC4802 Absolute Maximum Ratings(1) Operating Ratings(2) Main Input Voltage (VIN) .................................. –0.3V to +6V Enable Input Voltage (VEN).............................. –0.3V to +6V LED Driver Voltage (VD1) ................................ –0.3V to +6V Power Dissipation .....................................Internally Limited Lead Temperature (soldering, 10sec.)....................... 260°C Storage Temperature (Ts) .........................–65°C to +150°C Supply Voltage (VIN)..................................... +3.0V to +5.5V Enable Input Voltage (VEN) .................................... 0V to VIN LED Driver Voltage (VD1) ....................................... 0V to VIN Junction Temperature (TJ) ........................ –40°C to +125°C Junction Thermal Resistance EPAD SOIC-8L (θJA)..........................................41°C/W Electrical Characteristics VIN = VEN = 5V, RSET = 6.19kΩ; VD1 = 1.2V; TJ = 25°C, bold values indicate –40°C ≤ TJ ≤ 125°C; unless noted. Parameter Conditions (3) Current Accuracy Min Typ Max Units 747 830 913 mA Drop-out Where ILED = 90% of LED current seen at VDROPNOM = 1.2V, 100% brightness level 280 500 mV Ground/Supply Bias Current IOUT = 830mA 4.1 5.7 mA Shutdown Current VEN = 0V 0.01 1 µA 0.2 V PWM Dimming Enable Input Voltage (VEN) Logic Low 1.2 Logic High V Enable Input Current VIH > 1.2V 0.01 1 µA Current Source Delay (50% levels) Shutdown to on Standby to on On to Standby 40 2 0.3 60 µs µs µs Current Source Transient Time (10%-90%) TRISE TFALL 1 0.3 Stand-by to Shutdown Time VEN = 0V 10 20 µs µs 40 ms Notes: 1. Exceeding the absolute maximum rating may damage the device. 2. The device is not guaranteed to function outside its operating rating. 3. As determined by average current based on RSET resistance. January 2011 3 M9999-013111-B Micrel Inc. MIC4802 Typical Characteristics 1.4 1.2 VIN = 3.5V 1 0.8 VIN = 3.0V 0.6 0.4 500 VIN = 5.5V 0.8 LED CURRENT (A) LED CURRENT (A) 1 0.9 VIN = 5.5V Dropout Voltage vs. LED Current LED Current vs. LED Anode Voltage 450 VIN = 3.5V 0.7 0.6 VIN = 3.0V 0.5 0.4 0.3 0.2 0.2 0.1 5.5 5 4.5 4 3.5 3 5.5 2.5 4.5 4 3.5 3 LED ANODE VOLTAGE (V) Supply Bias Current vs. LED Anode Voltage Peak LED Current vs. RSET 10000 VIN = 3.5V VIN = 2.5V 4 3.5 3 2.5 1 10 500 fPWM = 200kHz 300 200 0 60 DUTY CYCLE (%) January 2011 600 fPWM = 5kHz 500 400 300 fPWM = 10kHz 200 0 80 20 100 40 60 80 100 DUTY CYCLE (%) Typical ILED vs. VLED 2 1.8 VIN = 5.0V 1.6 1.36 1.34 1.32 1.3 1.28 1.4 1.2 1 0.8 0.6 0.4 1.26 fPWM = 500kHz 40 fPWM = 1kHz 700 10000 LED CURRENT (A) RSET VOLTAGE (V) fPWM = 100kHz 20 1000 1.38 700 0 100 1.4 fPWM = 20kHz 100 600 800 1000 1200 1400 VIN = 5V RSET Voltage vs. LED Current 900 400 400 RSET (kΩ) LED Current vs. PWM Duty Cycle 600 200 0 1 LED BATTERY VOLTAGE (V) 800 VIN = 5V 100 RSET = 4.64kΩ 0 4.5 100 900 10 5 150 LED Current vs. PWM Duty Cycle 100 2 5.5 200 0 LED CURRENT (mA) 5 1 250 LED CURRENT (mA) 1000 3 300 800 6 4 350 0 2.5 VIN = 5.5V 7 ILED (mA) Supply Bias Current (mA) 5 LED BATTERY VOLTAGE (V) 8 400 50 0 0 LED CURRENT (mA) DROPOUT VOLTAGE (mV) LED Battery Voltage vs. LED Current VIN = 5V 1.24 0 200 400 600 800 1000 1200 1400 LED CURRENT (mA) 4 0.2 0 2.4 2.6 2.8 3 3.2 3.4 3.6 LED FORWARD VOLTAGE (V) M9999-013111-B Micrel Inc. MIC4802 Functional Characteristics January 2011 5 M9999-013111-B Micrel Inc. MIC4802 Functional Diagram Figure 1. MIC4802 Functional Block Diagram Block Diagram As shown in Figure 1, the MIC4802 consists of current mirrors set to copy a master current determined by RSET. The linear LED drivers have a designated control block for enabling and dimming of the LEDs. The MIC4802 dimming is controlled by the Ultra Fast PWMTM control block that receives PWM signals for dimming. Functional Description The MIC4802 is a single channel linear LED driver with a maximum 800mA current capability. The LED driver is designed to maintain proper current regulation with LED current accuracy of ±10%. The dropout is 280mV at 800mA. The low dropout of the linear drivers allows the LEDs to be driven directly from the battery voltage and eliminates the need for boost or large and inefficient charge pumps. The maximum LED current for each channel is set via an external resistor. Dimming is controlled by applying a PWM signal to the EN pin. The MIC4802 accommodates a wide PWM frequency range as outlined in the application information section. January 2011 6 M9999-013111-B Micrel Inc. MIC4802 VIN The input supply (VIN) provides power to the linear LED drivers and the control circuitry. The VIN operating range is 3V to 5.5V. A minimum bypass capacitor of 1µF should be placed close to the input (VIN) pin and the ground (GND) pin. Refer to the layout recommendations section for details on placing the input capacitor (C1). Peak LED Current vs. RSET ILED (mA) 1000 EN The EN pin is equivalent to the enable pin for the linear drivers on the MIC4802. It can also be used for dimming applying a PWM signal. See the PWM Dimming Interface in the Application Information section for details. Pulling the EN low for more than 40ms puts the MIC4802 into a low IQ sleep mode. The EN pin cannot be left floating; a floating enable pin may cause an indeterminate state on the outputs. The first pulse on the EN pin must be equal or greater than 60µs to wake the part up in a known state. This equates to an 8.3kHz PWM signal at equal or greater than 50% duty cycle. Higher PWM frequencies may be used but the first pulse must be equal or greater than 60µs. 100 10 1 1 10 100 1000 10000 RSET (kΩ) Figure 2. Peak LED Current vs. RSET D1 The D1 pins are the linear driver inputs for the LED. Connect the anode of the LED to VIN and the cathode to the D1 pins. All the D1 pins must be connected together. The D1 voltage at dropout is the minimum voltage required by the linear driver in order for the LED to be fully biased. RSET The RSET pin is used to set the peak current of the linear driver by connecting a RSET resistor to ground. The theoretical average LED current can be estimated by equation (1): ILED (mA) = 4920 * D / RSET (kΩ) (1) RSET (kΩ) = 4920 * D / ILED (mA) (2) GND The ground pin is the ground path for the linear driver. The ground of the input capacitor should be routed with low impedance traces to the GND pin and made as short as possible. Refer to the layout recommendations for more details. D is the duty cycle of the LED current during PWM dimming. When the device is fully ON the duty cycle equals 100% (D = 1). A plot of ILED versus RSET is shown in Figure 2. Due to DC losses across current paths internal and external to the package, the calculated RSET resistance equation is modified by a factor K, where K is calculated to be 0.280kΩ. RSET (kΩ) = 4920 * D / ILED (mA) + 0.280 (kΩ) (3) ILED (mA) = 4920 * D / ((RSET (kΩ) – 0.280 (kΩ)) (4) The modified LED current equation is more accurate in determining the actual LED current based on the RSET resistor value. January 2011 7 M9999-013111-B Micrel Inc. MIC4802 Application Information LED Current vs. PWM Duty Cycle Ultra Fast PWM™ Dimming Interface The MIC4802 supports a wide range of PWM control signal frequencies from 200Hz to 500kHz. This extremely wide range of control provides ultimate flexibility for handheld applications using high frequency PWM control signals. WLED dimming is achieved by applying a pulse width modulated (PWM) signal to the END pin. For PWM frequencies between 200Hz – 10kHz the MIC4802 supports a duty cycle range from 1% to 100%, as shown in Figure 3. The MIC4802 incorporates an internal shutdown delay to ensure that the internal control circuitry remains active during PWM dimming. This feature prevents the possibility of backlight flickering when using low frequency PWM control signals. The MIC4802 also supports Ultra Fast PWM™ frequencies from 20kHz to 500kHz. Due to input signal propagation delay, PWM frequencies above 20kHz have a non-linear relationship between the duty cycle and the average LED current, as shown in Figure 4 and 5. Figures 6 through 9 show the WLED current response when a PWM signal is applied to the END pin (1). 900 LED CURRENT (mA) 800 fPWM = 200kHz 400 300 200 fPWM = 500kHz 0 20 40 60 80 100 DUTY CYCLE (%) Figure 4. Channel Current Response to PWM Control Signal Frequencies from 50kHz to 500kHz Minimum Duty Cycle vs. Frequency 35 30 MINIMUM DUTY (%) LED Current vs. PWM Duty Cycle 25 20 15 10 5 0 100 900 LED CURRENT (mA) 500 0 From the low IQ sleep mode higher PWM frequencies above 15kHz require a logic high enable signal for 60μs to first enable the MIC4802 prior to PWM dimming. VIN = 5V fPWM = 1kHz 1000 10000 100000 1000000 FREQUENCY (Hz) 700 600 Figure 5. Minimum Duty Cycle for Varying PWM Frequency fPWM = 5kHz 500 fPWM = 100kHz 600 100 (1) 800 fPWM = 20kHz 700 400 300 fPWM = 10kHz 200 100 0 0 20 40 60 80 100 DUTY CYCLE (%) Figure 3. Average Current per LED Dimming by Changing PWM Duty Cycle for PWM Frequencies up to 20kHz Figure 6. PWM Signal at 1% Duty Cycle (Iavg = 8mA) January 2011 8 M9999-013111-B Micrel Inc. MIC4802 Thermal Consideration The MIC4802 thermal considerations involve calculating the junction temperature based on the voltage drop across the package and the LED current. The voltage drop across the package is equal to the voltage at D1 with respect to ground times the LED current. PLOSS = ILED * VD1 The temperature rise (ΔT) is calculated: ΔT = PLOSS * θJA Assuming the ILED is 800mA and VD1 is 500mV at 20°C room temperature, we can calculate the junction temperature: TJ = TA + ΔT TJ = 20°C + 0.4W * 41°C/W TJ = 20°C + 16.4°C = 36.4°C The junction temperature will be 36.4°C. Figure 7. PWM Signal at 20% Duty Cycle (Iavg = 160mA) Figure 8. PWM Signal at 50% Duty Cycle (Iavg = 400mA) Figure 9. PWM Signal at 80% Duty Cycle (Iavg = 640mA) January 2011 9 M9999-013111-B Micrel Inc. MIC4802 MIC4802 Typical Application Circuit Bill of Materials Item C1 Part Number Manufacturer C1608X5R0J225K TDK(1) 06036D225KAT2A AVX(2) GRM188R60J225KE19D Murata(3) VJ0603G225KXYAT Vishay(4) R42180 Seoul Semiconductor(5) LED RSET CRCW06036K19FKEA U1 MIC4802YME (4) Vishay Micrel, Inc.(6) Description Qty. Ceramic Capacitor, 2.2µF, 6.3V, X5R, Size 0603 1 3.8W High Power WLED 1 Resistor, 6.19kΩ, 1%, 1/16W, Size 0603 1 800mA Single Channel Ultra Fast PWM™ Linear WLED Driver 1 Notes: 1. TDK: www.tdk.com 2. AVX: www.avx.com 3. Murata: www.murata.com 4. Vishay: www.vishay.com 5. Seoul Semi: http://www.acriche.com/en 6. Micrel, Inc.: www.micrel.com January 2011 10 M9999-013111-B Micrel Inc. MIC4802 Layout Recommendations Top Layer Bottom Layer January 2011 11 M9999-013111-B Micrel Inc. MIC4802 Package Information 8-Pin SOIC (ME) 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. January 2011 12 M9999-013111-B