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. Issue 3 - July 2006 © Zetex Semiconductors plc 2006 Figure 1 Schematic diagram Figure 2 Performance graphs 1 www.zetex.com DN67 Reference Part number U1 Value Manufacturer Contact details ZXSC400E6 Zetex www.zetex.com Q1 FMMT617 Zetex www.zetex.com D1 ZHCS2000 Zetex www.zetex.com D2 LXHL-NW98 Lumileds www.lumileds.com L1 DO1608C-332 3.3H Coilcraft www.coilcraft.com C1 GRM42-6X5R226K6.3 22F Murata www.murata.com C2 GRM42-6X5R226K6.3 22F Murata www.murata.com R1(1) 17m⍀ Generic NA R2 0.82⍀ Generic NA Table 1 Bill of materials NOTES: (1) Actual in-circuit value, see notes overleaf Figure 3 Open circuit protection Additional BoM AD1 - 5V6 R3 - 1K⍀ www.zetex.com 2 Issue 3 - July 2006 © Zetex Semiconductors plc 2006 DN67 VIN L1 Q1 + C1 D1 U1 R1 GND R2 Figure 4 K’ D2 + A’ D2 C2 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 maximum influences efficiency, keep below 0.1⍀. forward voltage of the LED and less than 3. R1 is small and it is strongly advised to take the maximum VCE rating of the switching track resistance into account. A proven transistor, 15V in the case of the FMMT617. method is to source a 1A current from the The supply current in the open circuit Sense pin to the GND pin and check for 16condition is around 2mA. 17mV. This resistor can be made from a 22m⍀ in parallel with a 47m⍀ (or a single 15m⍀ resistor if available) with the PCB trace contributing the difference. Issue 3 - July 2006 © Zetex Semiconductors plc 2006 3 www.zetex.com DN67 Intentionally left blank Europe Americas Asia Pacific Corporate Headquarters Zetex GmbH Streitfeldstraße 19 D-81673 München Germany 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 Telefon: (49) 89 45 49 49 0 Fax: (49) 89 45 49 49 49 [email protected] 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] For international sales offices visit www.zetex.com/offices Zetex products are distributed worldwide. For details, see www.zetex.com/salesnetwork This publication is issued to provide outline information only which (unless agreed by the company in writing) may not be used, applied or reproduced for any purpose or form part of any order or contact or be regarded as a representation relating to the products or services concerned. The company reserves the right to alter without notice the specification, design, price or conditions of supply of any product or service. www.zetex.com 4 Issue 3 - July 2006 © Zetex Semiconductors plc 2006