DN79

DN79 ZXSC400 1W LED driver Neil Wolstenholme, Applications Engineer, Zetex Semiconductors plc Description ZXSC400 is configured to the reference design below. The target application is a 1W white LED driven from a two cell NiCd/NiMH or alkaline battery input for flashlights and high powered LED driving. The supply voltage for ZXSC400 reference design is: VIN = 1.8V ~ 3V. L1 22uH VIN D1 ZHCS1000 C1 100uF/6V3 U1 ZXSC400 VCC VDRIVE STDN ISENSE GND VFB Q1 FMMT617 C2 100uF/6V3 LED1 LXHL-PW01 R1 22mohm R2 0.82ohm GND Figure 1 Schematic diagram Ref. Value Package Part number Manufacturer Contact details Notes U1 N/A SOT23-6 ZXSC400E6 Zetex www.zetex.com Boost converter Q1 N/A SOT23 FMMT617 Zetex www.zetex.com Low sat NPN transistor D1 40V/1A SOT23 ZHCS1000 Zetex www.zetex.com 40V/1A Schottky diode L1 22uH/2.5A N/A DO3316P-223 Coilcraft www.coilcraft.com 22␮H/2.5A SMT inductor R1 22m⍀ 0805 Generic NA 0805 5% tolerance R2 0.82⍀ 0805 Generic NA 0805 5% tolerance C1 100␮F/6V3 1812 18126D107KAT2A AVX www.avx.com 100␮F/6V3/X5R/1812 C2 100␮F/6V3 1812 18126D107KAT2A AVX www.avx.com 100␮F/6V3/X5R/1812 LED1 1W N/A LXHL-PW01 Lumileds www.lumileds.com 1W white LED emitter Table 1 Bill of materials Issue 1 - May 2005 © Zetex Semiconductors plc 2005 1 www.zetex.com DN79 Performance Increasing efficiency On ZXSC400 reference design, R1 is set to 22mΩ to ensure that the LED current is regulated over the full input voltage range of 3V ~ 1.8V. For...