DN67

DN67 ZXSC400 solution for 1W high powered LED Mike Farley, Field Applications Engineer. December 2003 Description The ZXSC400, although designed for small LEDs in LCD backlighting, is sufficiently flexible to provide an efficient 1W solution producing a nominal 350mA constant current source from 2 NiMH or NiCd cells. Figure 1 Schematic diagram Figure 2 Performance graphs Issue 3 - July 2006 © Zetex Semiconductors plc 2006 1 www.zetex.com DN67 Reference U1 Q1 D1 D2 L1 C1 C2 R1(1) Part number ZXSC400E6 FMMT617 ZHCS2000 LXHL-NW98 DO1608C-332 GRM42-6X5R226K6.3 GRM42-6X5R226K6.3 Value Manufacturer Zetex Zetex Zetex Lumileds Contact details www.zetex.com www.zetex.com www.zetex.com www.lumileds.com www.coilcraft.com www.murata.com www.murata.com NA NA 3.3␮H 22␮F 22␮F 17m⍀ 0.82⍀ Table 1 Coilcraft Murata Murata Generic Generic R2 Bill of materials NOTES: (1) Actual in-circuit value, see notes overleaf Figure 3 Additional BoM AD1 - 5V6 R3 - 1K⍀ Open circuit protection www.zetex.com 2 Issue 3 - July 2006 © Zetex Semiconductors plc 2006 DN67 VIN L1 + C1 U1 R1 GND R2 K’ D2 + C2 A’ D2 Q1 D1 Figure 4 Layout suggestion Note For these approximate layout dimensions, R1 is 15m⍀. See note 3. Notes: 1. D1 can be exchanged with a SOT23 4. Open circuit protection can be added as ZHCS1000 with a loss of 5% efficiency. shown below. The voltage rating of the small signal Zener diode ZD1 is not critical. 2. Inductor DCR (DC resistance) strongly It must be greater than the ma...