ZXLD381EV1 USER GUIDE Description The ZXLD381 is a single or multi cell LED driver designed for applications requiring step-up voltage conversion from a very low input voltage and on/off enable control. The IC generates constant current pulses that are ideal for driving single or multiple LEDs over a wide range of operating voltages. The IC can start up under full load and operates down to an input voltage of below 0.9V. The ZXLD381 is offered in the space saving SOT23-3 package or in die form, offering an excellent cost versus performance solution for single cell LED driving applications. The ZXLD381 uses a PFM control technique to drive an internal switching transistor which exhibits a low saturation resistance. This ensures high efficiency, even for input voltages as low as 1.0V. Features Applications • • • • • • • • LED flashlights and torches • LED backlights • White LED driver 85% Efficiency User adjustable output current Single cell operation (0.9V minimum) Low saturation voltage switching transistor SOT23-3 package Available also in Die form Simple Application circuit Ordering information Typical application circuit L1 3 Vin ZXLD381 Vout 2 GND Please note evaluation boards are subject to availability and qualified leads. 4u7 SW1 1 ORDER NUMBER ZXLD381EV1 ZXLD381 Batt LED1 LED2 LED3 GND Issue 2 - June 2009 © Diodes Incorporated, 2009 www.diodes.com ZXLD381EV1 Reference design ZXLD381EV1 evaluation board is designed to drive up to 3 white LEDs in parallel. The target application is single cell flashlights and torches. This board is designed to accept a single AAA cell as the voltage source. Please note that the board does not have reverse polarity protection, so the battery must be fitted correctly. The circuit is switched on using the momentary push button and goes off when the button is released. The design demonstrates the simplicity possible with this device: the capacitor C1 may be omitted if the battery is close to the device but is needed otherwise. The evaluation board is fitted with three T1¼ white LEDs, and to use these, the jumper P1 must be fitted. External LEDs may be connected via CON1 and CON2, marked LED +ve and LED –ve respectively. In this case the jumper must be removed. For other reference designs or further applications information please refer to the ZXLD381 datasheet. Schematic diagram L1 4u7 SW1 3 Batt Batt 2 GND ZXLD381 Vout LED+ve 1 C1 4.7uF 1 +2 Vin P1 2 1 ZXLD381 Header 2 LED1 LED2 LED3 LED-ve GND Issue 2 - June 2009 www.diodes.com © Diodes Incorporated, 2009 2 ZXLD381EV1 Components list Ref Value U1 L1 C1 LED1,2,3 LED Driver 4.7uH 4.7uF 25V X7R 5mm White LED Package SOT23-3 ME3220 Part Number Manufacturer ZXLD381FHTA ME3220-472MLB C1206C475K3RAC 10000mcd@30mA Zetex Coilcraft Kemet (generic) Contact Details www.zetex.com www.coilcraft.com www.kemet.com Performance graphs Input Current v Batt Voltage 200 180 160 Batt ma 140 120 100 Iin 80 60 40 20 0 0.9 1 1.1 1.2 1.3 1.4 1.5 Batt Volts LED Current v Batt Voltage 45 40 35 LED mA 30 25 20 15 10 5 0 0.9 1 1.1 1.2 1.3 1.4 1.5 Batt Volts Issue 2 - June 2009 www.diodes.com © Diodes Incorporated, 2009 3 ZXLD381EV1 % efficiency v Batt Voltage 100 90 80 70 % 60 50 40 30 20 10 0 0.9 1 1.1 1.2 1.3 1.4 1.5 Batt Volts ZXLD381EV1 operation Component layout diagram ZXLD381EV1 set-up and test 1. 2. 3. 4. 5. 6. 7. Preset the PSU to 1.5V with a current limit of around 200mA. Close the link P1. Connect Batt +ve and Batt -ve to the positive and zero volts respectively, of a battery or power supply. Ensure that the connections are made correctly, as the board is not reverse polarity protected. Turn on the PSU. The LEDs should illuminate. The input current should measure between 120mA - 160mA. Turn off the PSU Layout considerations PCB tracks should be kept as short as possible to minimize ground bounce. It is particularly important to mount the coil and the input/output capacitors close to the device to minimize parasitic resistance and inductance, which will degrade efficiency. Issue 2 - June 2009 www.diodes.com © Diodes Incorporated, 2009 4 ZXLD381EV1 Intentionally blank Issue 2 - June 2009 www.diodes.com © Diodes Incorporated, 2009 5 ZXLD381EV1 Intentionally blank Issue 2 - June 2009 www.diodes.com © Diodes Incorporated, 2009 6 ZXLD381EV1 Intentionally blank Issue 2 - June 2009 www.diodes.com © Diodes Incorporated, 2009 7 ZXLD381EV1 IMPORTANT NOTICE DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARD TO THIS DOCUMENT, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION). Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes without further notice to this document and any product described herein. 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