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| IXYS Features: * * * * 1.1V to 5.5V Input Range 2 Amp Peak Switch Current High Efficiency > 80% 20V Maximum Output with Over-Voltage Protection * LED Intensity Control * 1.0 MHz Fixed Frequency Switching * 8 Lead SOIC Package MX841 White LED Step-Up Converter General Description The MX841 is a fixed frequency, constant current source step-up DC/DC converter. The output current is directly regulated making the MX841 ideal for driving series connected white light emitting diodes (LED's) in backlight applications. The MX841 powers up to 3 series white LED's at 1.1V, and 20 series/parallel white LED's at 5.0V. The MX841 features a 1.0MHz switching frequency to accommodate the use of small capacitors and a small inductor necessary in size sensitive portable applications. Light intensity and shutdown are conveniently controlled by a single analog voltage. Power efficiency and battery life are extended through the use of a high voltage, low RDSON Nchannel MOSFET switch. The MX841 is designed to operate over a temperature range of -40C to +85C, and is available in an SOIC-8 Package, with or without an Exposed Pad in Tube or on Tape and Reel. (Alternate package types available upon request). Applications: * White LED Display Backlighting - Low Voltage: Mobile Phones, PDA's, MP3 Players, Digital Cameras - High Drive Current: Vehicle Instrumentation Panels Ordering Information Part No. 17000-00TU 17000-00TR 17043-00TU 17043-00TR Description SOIC-8 Standard Tube SOIC-8 Standard T&R SOIC-8 Exposed Pad Tube SOIC-8 Exposed Pad T&R Qty 100 2500 100 2500 Functional Block Diagram Typical Application VDD SW SW Vbattery Vboost osc CTL/SLEEP err amp/ comparator driver 5 1 4 VDD SW SW OVD 6 Analog Gnd band gap + compare OVD CTRL Isense 7 CTL/ SLEEP MX841 Isense 8 Switch Gnd sleep det bias gen Analog GND 2 Switch GND 3 Rsense MX841 Drawing No. 17023 Preliminary 1 03/10/05 www.ixys.net MX841 Absolute Maximum Ratings (Voltages with respect to GND=0V) Parameter Min VDD Supply Voltage -0.4 CTRL Voltage GND-0.4 ISENSE Voltage GND-0.4 SW Voltage -0.4 OVD Voltage -0.4 Operating Ambient Temperature Range -40 Storage Temperature Range -55 Operating Junction Temperature Range -40 Power Dissipation Standard SOIC JA = 114C/W TA = 27C Exposed Pad SOIC JA = 50C/W ESD Warning Max +6.5 VDD+0.4 VDD+0.4 +24.0 +24.0 +85 +150 +125 775 1.75 Unit V V V V V Co Co Co mW W IXYS Absolute Maximum Ratings are stress ratings. Stresses in excess of these ratings can cause permanent damage to the device. Functional operation of the device at these or any other conditions beyond those indicated in the operational sections of this data sheet is not implied. Exposure of the device to the absolute maximum ratings for an extended period may degrade the device and affect its reliability. ESD (electrostatic discharge) sensitive device. Although the MX841 features proprietary ESD protection circuitry, permanent damage may be sustained if subjected to high energy electrostatic discharges. Proper ESD precautions are recommended to avoid performance degradation or loss of functionality. VDD=3.0V, RSENSE=5, VCTRL=1.0V, L=6.8H, CBYP=1F, TA = -40oC to +85oC, Typical Values at +25oC Unless otherwise specified DC Electrical Characteristics Parameter Supply Voltage Supply Current Overvoltage Supply Current Operating Sleep Current CTRL Bias Current ISENSE Bias Current OVD Bias Current Over Voltage Threshold CTRL / VRSENSE VCTRL Sleep Mode SW On Resistance Switch Current SW Voltage Range SW Leakage Current VCTRL Condition TA = 25 C o Min 1.1 Typ 0.5 6 7 Max 5.5 0.8 2 Unit V mA A A A A A Not Switching: VCTRL = 260mV VRSENSE > 13 X VCTRL Switching: VCTRL= VDD, VRSENSE=GND TA = +25oC VCTRL < 100mV TA = +85oC -10 OVD = 18V OVD Rising OVD Falling VCTRL Rising VCTRL Falling VSW = 0.1V VSW = 0.5V VDD=1.2V, L=33H VDD=5.5V, L=2.5H VCTRL >260mV VCTRL = GND 18.5 -7 20 0 22 13 260 100 1.9 2.2 30 2 VDD VSCHOTTKY 0.1 0.3 0 VDD 20 V V V/V mV mV mA A V A A V OVD = VSW = 18V TA = +25oC TA = +85oC MX841 Drawing No. 17023 Preliminary 2 03/10/05 www.ixys.net MX841 AC Electrical Characteristics Parameter Oscillator Frequency Duty Cycle IXYS Condition Min 0.6 Typ 1.0 72.5 Max 1.3 Unit MHz % VDD=3.0V, RSENSE=5; VCTRL=1.0V, L=6.8H; CBYP=1F, TA = -40oC to +85oC, Typical Values at +25oC Unless otherwise specified Pin Description Pin No. 1, 4 Pin Name SW Description Power Switch. Connects the drain of the internal high voltage N-channel MOSFET to the Inductor and Schottky Diode to generate the LED boost voltage. This voltage is determined by the total forward bias voltage of the LED series string and the Isense resistor value. (Note: Both pins must be connected.) Analog Ground (Note: Must be connected to a low noise ground source.) Switch Ground (Note: Must be connected to a high current ground source.) Input supply pin. Input range from 1.1 to 5.5 volts. Must be bypassed with a low ESR capacitor to GND. Over Voltage Detect input. Compares the LED boots voltage to the internal voltage reference. If the boost voltage rises above 22V the OVD circuit disables the oscillator and N-channel MOSFET until the boost voltage falls below 18.5V. Must be bypassed with a low ESR capacitor to GND. Shutdown and Intensity Control Input. A control voltage above 260mV enables device operation. A control voltage below 100mV disables device operation. LED intensity is linearly adjusted with voltages between 260mV and VDD. Current Sense Input. The LED bias current is set by connecting a carbon composite or monolithic resistor from this input to Ground. ISENSE regulates this current to 1/13 of the CTRL input voltage. 2 3 5 Analog GND Switch GND VDD 6 OVD 7 CTRL 8 Isense MX841 Drawing No. 17023 Preliminary 3 03/10/05 www.ixys.net MX841 Functional Description The MX841 is specifically designed to be operated from a single cell battery source. The step-up voltage necessary for the constant current source to drive up to 5 white LED's in series, or multiple strings of white LED's, is achieved with minimal external components. (See Application Schematics on pages 1&4). Setting the LED Current The regulated output current is determined by the selection of the sense Resistor connected from the ISENSE input to ground, and the maximum user defined voltage of the CTRL input. The desired output current, (typically 15mA to 20mA for white LEDs), is derived using the following formula for the RSENSE value: RSENSE = (VCTRL X 1/13) / ILED. Current Regulation / Light Intensity Control The ISENSE voltage is fed into an ErrorAmp/Comparator. The user defined Control Voltage applied at the CTRL input is scaled by a gain factor of 1/13 and compared to the ISENSE voltage. If the scaled control voltage is greater than the ISENSE voltage, the 1.0MHz oscillator signal driving the N-Channel MOSFET will be enabled. Once the ISENSE voltage reaches the scaled CTRL voltage the oscillator signal is modulated on and off by the ErrorAmp/Comparator to maintain the desired regulated output current. IXYS Light intensity is controlled by reducing the voltage at the CTRL input. As the CTRL input voltage is reduced below the user defined maximum value, the oscillator signal driving the N-Channel MOSFET is interrupted by the ErrorAmp/Comparator. The pulse skip modulating of the N-Channel MOSFET causes a reduction in the regulated current equal to the ratio of the reduced CTRL voltage to the maximum CTRL voltage. Sleep Mode The MX841 goes into sleep mode when the VCTRL input is less than 100mV. All circuits except VCTRL detection are shutdown and the supply current falls to 6uA. Once the VCTRL input rises above 260mV the MX841 resumes normal operation. Over Voltage Detection The MX841 will go into a shutdown state to avoid an over voltage condition if the current path between the SW output and the RSENSE input is interrupted. A voltage reference and comparator circuit evaluates the voltage potential at the OVD input and shuts down the oscillator and NChannel MOSFET if an over voltage condition is detected. Normal operation is resumed once the OVD input voltage falls below the reference voltage, (20V typical). MX841 Drawing No. 17023 Preliminary 4 03/10/05 www.ixys.net MX841 Circuit Application Driving 15 White LED's Vbattery 3.0V - 5.0V 6.8uH Ipk=1.7A 22uF 35V 0.1uF in Parallel 1N5817 VF=0.3V Vboost IXYS 22uF 35V 0.1uF in Parallel 26K Ohms @ 3.0V 57K Ohms @ 5.0V 5 1 4 SW VDD SW OVD 6 20K Ohms (Dimming Control) CTRL 7 CTL/SLEEP MX841 Isense 8 Analog GND 2 Switch GND 3 Rsense 5 Ohms 5 Ohms 5 Ohms 8-LEAD SOI IXYS Corporation makes no representations or warranties with respect to the accuracy or completeness of the contents of this publication and reserves the right to make changes to specifications and product descriptions at any time without notice. Neither circuit patent licenses nor indemnity are expressed or implied. Except as set forth in IXYS' Standard Terms and Conditions of Sale, IXYS Corporation assumes no liability whatsoever, and disclaims any expressed or implied warranty, relating to its products including, but not limited to, the implied warranty of merchantability, fitness for a particular purpose, or infringement of any intellectual property right. MX841 Drawing No. 17023 Preliminary 5 03/10/05 www.ixys.net IXYS IXYX Corporation 3540 Bassett Street Santa Clara, CA 925054 Tel: 1-408-892-0700 Fax: 1-408-496-0670 e-mail:sales@ixys.net SALES OFFICES AMERICAS Eastern Region [AL, AR, CT, DC, FL, GA, IA, IL, IN, KS, KY, LA, MA, MD, ME, MI, MN, MO, MS, NC, ND, NE, NH, NJ, NY, OH, OK, PA, RI, SC, SD, TN, TX, VA, VT, WI, WV, Americas: Canada, Brazil] World Wide Sales Offices Germany IXYS Semiconductor GMBH Edisonstrasse 15 D- 68623 Lampertheim Germany Tel : +49-6206-503203 Fax - +49-6206-503286 Italy IXYS Via C. Colombo 10/A I-20066 Melzo (Milano) Tel: +39-02-95737160 Fax: +39-02-95738829 Sweden IXYS Sales Comptronic AB Box 167 S-16329 Spanga Tel: +46-862-10370 Fax: +46-862-10371 United Kingdom IXYS UK Sales Marco Polo House Cook Way Bindon Road Taunton, Somerset TA2 6BG Tel: +44-1-823 352541 Fax: +44-1-823 352797 ASIA / PACIFIC Asian Headquarters IXYS Room 1016, Chia-Hsin, Bldg II, 10F, No. 96, Sec. 2 Chung Shan North Road Taipei, Taiwan R.O.C. Tel: 886-2-2523-6368 Fax: 886-2-2523-6368 IXYS Groveland, FL Tel: 1-352-429-3892 Fax: 1-352-429-3899 mproctor@clare.com Western Region [AK, AZ, CA, CO, HI, ID, MT, NM, NV, OR, UT, WA, WY, Americas: Canada, Mexico] IXYS 3540 Bassett Street Santa Clara, CA 95054 Tel: 1-408-982-4353 Fax: 1-408-496-0670 EUROPE European Headquarters IXYS Semiconductor GMBH Edisonstrasse 15 D- 68623 Lampertheim Germany Tel : +49-6206-503203 Fax - +49-6206-503286 SALES OFFICES France Eurocomposant 144, Av. J. Kessel F-78960 Voisins-le-Bretonneux, France Tel : +33-130-649515 Fax : +33-130-436827 IXYS cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in this IXYS product. No circuit patent licenses nor indemnity are expressed or implied. IXYS reserves the right to change the specification and circuitry, without notice at any time. The products described in this document are not intended for use in medical implantation or other direct life support applications where malfunction may result in direct physical harm, injury or death to a person. Specification: MX841 (c)Copyright 2005, IXYS Corporation All rights reserved. Printed in USA. MX841 Drawing No. 17023 Preliminary 6 03/10/05 www.ixys.net |
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