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AN44 Datasheet(PDF) 4 Page - Zetex Semiconductors |
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AN44 Datasheet(HTML) 4 Page - Zetex Semiconductors |
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4 / 6 page 
AN44 www.zetex.com 4 Issue 2 - July 2006 © Zetex Semiconductors plc 2006 As the TOFF period is nominally 1.7µs, the current should have time to reach zero. However, 1.5µs is rather close to 1.7µs and it is possible that, over component tolerances, the coil current will not reach zero, but this is not a big issue as the remaining current will be small. Note that, because of the peak current measurement and switch-off, it is not possible to get the dangerous ‘inductor staircasing’ which occurs in converters with fixed TON times. The current can never exceed IPEAK, so even if it starts from a finite value (i.e. continuous mode) it will not exceed the IPEAK. The LED current will therefore be approximately the average of 680mA and zero = 340mA (it will not be exactly the average, because there is a 200ns period at zero current, but this is small compared with the IPEAK and component tolerances). Ref Value Part number Manufacturer Contact details Comments U1 ZXSC310E5 Zetex www.zetex.com LED Driver in SOT23-5 Q1 ZXMN6A07F Zetex www.zetex.com N-channel MOSFET in SOT23 D1 1A / 40V ZHCS1000 Zetex www.zetex.com 1A Schottky diode in SOT23 D2 6V8 Generic Generic 6V8 Zener diode L1 22 H DO3316P-223 Coilcraft www.coilcraft.com R1 50m Generic Generic 0805 size R2 1k2 Generic Generic 0805 size C1 100 F/25V Generic Generic C2 1 F/10V Generic Generic C3 2.2 F/25V Generic Generic Table 1 Bill of materials |
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