ZXSC400EV7 USER GUIDE DESCRIPTION The ZXSC400 is a voltage mode boost converter in a SOT23-6 package. The low feedback voltage VFB input allows the current in a chain of LEDs to be set accurately. The ZXSC400EV7 is designed to drive one or two 3W LEDs at a constant current of 700mA from an input voltage between 1.8V and 3.0V. The board is fitted with a socket for use with a variety of LED types. The board is open-circuit-LED protected and intended to be used with two alkaline, NiCad or NiMH batteries. FEATURES • Drives one or two 3W LEDs. • Typical efficiency of 80%. • Open-circuit-LED protected. • High-sided current sensing. • Compatible with Future LED boards. APPLICATIONS • LED torches and flashlights. • Portable illumination. • Emergency lights. TYPICAL APPLICATION CIRCUIT ORDERING INFORMATION ORDER NUMBER ZXSC400EV7 Please note evaluation boards are subject to availability and qualified leads. Figure 1. ZXSC400EV7 Evaluation Board. Issue 2 – February 2009 © Diodes Incorporated, 2009 www.zetex.com www.diodes.com ZXSC400EV7 REFERENCE DESIGN The ZXSC400EV7 uses the circuit below. The target application is a 3W white LED being driven from two NiCd/NiMH batteries for torches, but the device is also excellent for general high powered LED driving. Q1 and Q2 form a pseudo-Darlington pair, which provides enough current gain for switching currents of above 1.5A. The turnoff speed is enhanced by D2, which provides a discharge path for Q1. The current monitor ZXCT1009 is used for monitoring the LED current flowing through the low-ohmic resistor R2. The resistor R2 transforms the LED current into an accurate and low-loss sensing voltage for the VFB pin of the ZXSC400. Open circuit protection is provided by Zener diode D3, which causes VFB to be held above 300mV when the output is over voltage. Since the Isense threshold of ZXSC400 is quite low (typically 28mV), noise due to heavy collector switching currents may cause the system to work in unstable manner. In order to prevent this from happening, the waveform on the Isense pin is enhanced by adding the edges from the collector waveform via the high pass filter formed by C4 and R6. The ZXSC400EV7 operates from a supply voltage between approximately 1.8V and 3.0V. For other reference designs or further applications information, please refer to the ZXSC400 datasheet. Figure 2. ZXSC400EV7 Schematic Diagram. Issue 2 – February 2009 www.zetex.com www.diodes.com © Diodes Incorporated 2009 2 ZXSC400EV7 COMPONENTS LIST Ref Value Package Part Number Manufacturer Notes U1 U2 Q1 Q2 D1 D2 D3 L1 N/A N/A N/A N/A 40V/2A 40V/400mA 6.8V/0.25W 15uH/3A SOT23-6 SOT23 SOT23 SOT23 SOT23-6 SOD323 SOT23 N/A ZXSC400E6 ZXCT1009 ZXTN25012EFH ZXTN25012EFL ZHCS2000 ZHCS400 BZX84-C6V8 DO3316P-153 NPI31W150MTRF 74456115 Boost converter Current monitor Low sat. NPN transistor Low sat. NPN transistor 40V/1A Schottky diode 40V/400mA Schottky diode 6.8V/ 0.25W Zener diode 15uH/3A SMT Inductor R1 R2 R3 R4 R5 R6 R7 C1 C2 20mΩ 50mΩ 820Ω 82Ω 4.7Ω 10Ω 100Ω 22µF/16V 4.7µF/10V 0805 0805 0805 0805 0805 0805 0805 1210 1206 C3 C4 220nF/6V3 330pF/6V3 0805 0805 Diodes Zetex Diodes Zetex Diodes Zetex Diodes Zetex Diodes Zetex Diodes Zetex Diodes Zetex Coilcraft NIC Comps. Wurth Generic Generic Generic Generic Generic Generic Generic Murata Kemet Murata NIC Comps Generic Generic GRM32ER61C226KE20L C1206C475K8RAC GRM31CR71A475KA01L NMC1206X7R475K10 0805 +/-1% tolerance 0805 +/-1% tolerance 0805 +/-1% tolerance 0805 +/-5% tolerance 0805 +/-5% tolerance 0805 +/-5% tolerance 0805 +/-5% tolerance X5R +/-10% tolerance X7R +/-10% tolerance X7R +/-10% tolerance COG/NPO +/-5% tolerance Figure 3. Performance graphs. Issue 2 – February 2009 www.zetex.com www.diodes.com © Diodes Incorporated 2009 3 ZXSC400EV7 ZXSC400EV7 VERIFICATION ZXSC400EV7 2 CELL 3W LED DRIVER EVALUATION BOARD LED K OFF SW1 L1 SK1 R2 U2 C4 D1 R4 Q2 D3 R6 Q1 PO W ER C1 1 ON C2 R7 C3 U1 R5 R1 R3 LED A Figure 4. Evaluation PCB ZXSC400EV7 Set-up and Test 1. Connect VIN and GND to positive and zero volts of PSU supply respectively. 2. Set the PSU to 3V. 3. Turn on PSU. 4. The LED should illuminate and be regulated at 700mA +/-5%. 5. The input current should measure between 1A ~ 1.2A THIS IS A FUNCTIONAL EVAL BOARD. Issue 2 – February 2009 www.zetex.com www.diodes.com © Diodes Incorporated 2009 4 ZXSC400EV7 LAYOUT CONSIDERATIONS The PCB tracks have been kept as short as possible to minimise ground bounce, and the ground pin of the device is soldered directly to the ground plane. The inductor, and the input and output capacitors, have been mounted close to the device. This is particularly important in order to minimise the parasitic resistance and inductance, which would degrade efficiency. The Isense pin is a high impedance input, so PCB track lengths to pin this have been kept as short as possible to reduce noise pickup. ZXSC400EV7 2 CELL 3W LED DRIVER EVALUATION BOARD LED K OFF SW1 L1 SK1 R2 U2 C4 D1 R4 Q2 D3 R6 Q1 PO WER U1 C1 1 ON C2 R7 C3 R5 R1 R3 LED A Top Silk Top Copper Bottom Copper Drill File Figure 5. Layout of the ZXSC400EV7. Issue 2 – February 2009 www.zetex.com www.diodes.com © Diodes Incorporated 2009 5 ZXSC400EV7 INTENTIONALLY BLANK Issue 2 – February 2009 www.zetex.com www.diodes.com © Diodes Incorporated 2009 6 ZXSC400EV7 INTENTIONALLY BLANK Issue 2 – February 2009 www.zetex.com www.diodes.com © Diodes Incorporated 2009 7 ZXSC400EV7 Definitions Product change Diodes Incorporated reserves the right to alter, without notice, specifications, design, price or conditions of supply of any product or service. Customers are solely responsible for obtaining the latest relevant information before placing orders. Applications disclaimer The circuits in this design/application note are offered as design ideas. It is the responsibility of the user to ensure that the circuit is fit for the user’s application and meets with the user’s requirements. No representation or warranty is given and no liability whatsoever is assumed by Diodes Inc. with respect to the accuracy or use of such information, or infringement of patents or other intellectual property rights arising from such use or otherwise. Diodes Inc. does not assume any legal responsibility or will not be held legally liable (whether in contract, tort (including negligence), breach of statutory duty, restriction or otherwise) for any damages, loss of profit, business, contract, opportunity or consequential loss in the use of these circuit applications, under any circumstances. Life support Diodes Zetex products are specifically not authorized for use as critical components in life support devices or systems without the express written approval of the Chief Executive Officer of Diodes Incorporated. As used herein: A. Life support devices or systems are devices or systems which: 1. are intended to implant into the body or 2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in significant injury to the user. B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or to affect its safety or effectiveness. Reproduction The product specifications contained in this publication are issued to provide outline information only which (unless agreed by the company in writing) may not be used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a representation relating to the products or services concerned. Terms and Conditions All products are sold subjects to Diodes Inc. terms and conditions of sale, and this disclaimer (save in the event of a conflict between the two when the terms of the contract shall prevail) according to region, supplied at the time of order acknowledgement. For the latest information on technology, delivery terms and conditions and prices, please contact your nearest Diodes sales office. Quality of product Diodes Zetex Semiconductors Limited is an ISO 9001 and TS16949 certified semiconductor manufacturer. To ensure quality of service and products we strongly advise the purchase of parts directly from Zetex Semiconductors or one of our regionally authorized distributors. For a complete listing of authorized distributors please visit: www.zetex.com or www.diodes.com. Diodes Zetex Semiconductors does not warrant or accept any liability whatsoever in respect of any parts purchased through unauthorized sales channels. ESD (Electrostatic discharge) Semiconductor devices are susceptible to damage by ESD. Suitable precautions should be taken when handling and transporting devices. The possible damage to devices depends on the circumstances of the handling and transporting, and the nature of the device. The extent of damage can vary from immediate functional or parametric malfunction to degradation of function or performance in use over time. Devices suspected of being affected should be replaced. Green compliance Diodes Zetex Semiconductors is committed to environmental excellence in all aspects of its operations which includes meeting or exceeding regulatory requirements with respect to the use of hazardous substances. Numerous successful programs have been implemented to reduce the use of hazardous substances and/or emissions. All Diodes Zetex components are compliant with the RoHS directive, and through this it is supporting its customers in their compliance with WEEE and ELV directives. Product status key: “Preview” “Active” “Last time buy (LTB)” “Not recommended for new designs” “Obsolete” Datasheet status key: “Draft version” “Provisional version” “Issue” Future device intended for production at some point. Samples may be available Product status recommended for new designs Device will be discontinued and last time buy period and delivery is in effect Device is still in production to support existing designs and production Production has been discontinued This term denotes a very early datasheet version and contains highly provisional information, which may change in any manner without notice. This term denotes a pre-release datasheet. It provides a clear indication of anticipated performance. However, changes to the test conditions and specifications may occur, at any time and without notice. This term denotes an issued datasheet containing finalized specifications. However, changes to specifications may occur, at any time and without notice. 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