DN70 ZXSC400 Driving 2 serial high power LEDs Description This design note shows the ZXSC400 driving 2 serial LEDs. The input voltage ranges from 2V to 3.6V with a maximum output current of 360mA from 2.6V input. Figure 1 shows a typical constant current solution with the ZXSC400 driving two 1W LEDs in series. The wide input voltage range allows the use of different battery cell combinations. This could be dual alkaline cells with voltage starting from 3V down to 2V or triple NiCad/NiMH cells with voltage starting from 3.6V down to 2.7V. D1 L1 VIN=1.8V to 3.6V Q1 C2 U1 C1 Vcc Vdrive Stdn Isense Gnd VFB ZXSC400 R1 Figure 1 Ref. Value R2 Schematic diagram Part number Manufacturer Comments U1 ZXSC400E6 Zetex LED driver in SOT23-6 Q1 ZXTN25012EFH Zetex Low sat. NPN transistor in SOT23 D1 2A ZHCS2000 Zetex 2A Schottky in SOT23 L1 22H Generic Generic ISAT = 2A R1 18m⍀ Generic Generic 0805 size R2 820m⍀ Generic Generic 0805 size R3 1K⍀ Generic Generic 0805 size C1 22uF/10V Generic Generic C2 100uF/10V Generic Generic C3 220nF/10V Generic Generic Table 1 Issue 3 - July 2007 © Zetex Semiconductors plc 2007 0805 size Bill of materials 1 www.zetex.com DN70 Typical operating characteristics (For typical application circuit where Tamb = 25°C unless otherwise stated) 100 0.4 Output Current (A) Efficiency (%) 90 80 70 60 50 3.6 3.4 3.2 3 2.8 2.6 2.4 2.2 0.2 0.0 2 3.6 3.4 3.2 Input Voltage (V) Input Voltage vs Efficiency 2.8 2.6 2.4 2.2 2 2.2 2 Input Voltage vs Output Current 1.6 8 1.2 6 Output Voltage (V) Input Current (A) 3 Input Voltage (V) 0.8 0.4 0.0 4 2 0 3.6 3.4 3.2 3 2.8 2.6 2.4 2.2 3.6 2 3.4 3.2 2.8 2.6 2.4 Input Voltage vs Output Voltage Input Voltage vs Input Current Figure 2 www.zetex.com 3 Input Voltage (V) Input Voltage (V) Performance graphs 2 Issue 3 - July 2007 © Zetex Semiconductors plc 2007 DN70 Intentionally left blank Issue 3 - July 2007 © Zetex Semiconductors plc 2007 3 www.zetex.com DN70 Definitions Product change Zetex Semiconductors 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 Zetex 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. Zetex 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. 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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/salesnetwork 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. 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Samples may be available “Active” Product status recommended for new designs “Last time buy (LTB)” Device will be discontinued and last time buy period and delivery is in effect “Not recommended for new designs” Device is still in production to support existing designs and production “Obsolete” Production has been discontinued Datasheet status key: “Draft version” This term denotes a very early datasheet version and contains highly provisional information, which may change in any manner without notice. “Provisional version” 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. “Issue” This term denotes an issued datasheet containing finalized specifications. However, changes to specifications may occur, at any time and without notice. Zetex sales offices Europe Americas Asia Pacific Corporate Headquarters Zetex GmbH Kustermann-park Balanstraße 59 D-81541 München Germany Telefon: (49) 89 45 49 49 0 Fax: (49) 89 45 49 49 49 [email protected] Zetex Inc 700 Veterans Memorial Highway Hauppauge, NY 11788 USA Zetex (Asia Ltd) 3701-04 Metroplaza Tower 1 Hing Fong Road, Kwai Fong Hong Kong Zetex Semiconductors plc Zetex Technology Park, Chadderton Oldham, OL9 9LL United Kingdom Telephone: (1) 631 360 2222 Fax: (1) 631 360 8222 [email protected] Telephone: (852) 26100 611 Fax: (852) 24250 494 [email protected] Telephone: (44) 161 622 4444 Fax: (44) 161 622 4446 [email protected] © 2007 Published by Zetex Semiconductors plc www.zetex.com 4 Issue 3 - July 2007 © Zetex Semiconductors plc 2007