DN85 ZXSC400 1W/3W buck LED drivers Ray Liu, Applications Engineer, Zetex Semiconductors Description In Figure 1, ZXSC400 is configured as a high efficiency buck LED driver. The target applications are either 1W (350mA) or 3W (700mA) drivers for white LED driven from a 4 cell battery, or a 2 alkaline cell input for flashlights. The supply voltage for ZXSC400 reference design is: VIN = 3.8V to 6V. Parts lists for 1W and 3W design are shown in Table 1 and Table 2 respectively. Performance data is measured based on two different LED's VF binning with 0.3V VF difference. C3 L1 VIN = 4V to 6V D1 C2 U1 VCC C1 Q1 VDRIVE Stdn VFB GND ISENSE R3 R2 ZXSC400 R1 Figure 1 Issue 1 - August 2007 © Zetex Semiconductors plc 2007 Schematic diagram 1 www.zetex.com DN85 Ref. Value Package Part number Manufacturer Contact details Notes U1 N/A SOT23-6 ZXSC400E6 Zetex www.zetex.com LED Driver Q1 N/A SOT23 ZXTN25012EFL Zetex www.zetex.com Low sat NPN transistor D1 40V/0.75A SOT23 BAT750 Zetex www.zetex.com 40V/0.75A Schottky diode L1 47H N/A 744052470 Wurth Elektronik www.we-online.com ISAT = 520mA R1 62m⍀ 0805 Generic N/A 0805 1% R2 10⍀ 0805 Generic N/A 0805 5% R3 47⍀ 0805 Generic N/A 0805 5% C1 4.7F/10V 1206 Generic N/A X7R/X5R C2 100pF/10V 0805 Generic N/A COG/NPO C3 1uF/10V Generic N/A X7R/X5R optional 0805 Table 1 www.zetex.com Bill of materials for 1W LED 2 Issue 1 - August 2007 © Zetex Semiconductors plc 2007 DN85 Performance 90 0.4 Output Current (A) 0.5 Efficiency (%) 100 80 70 60 VF~3.3 5.8 5.4 5 4.6 0.2 0.1 VF~3.6 VF~3.3 50 6.2 0.3 4.2 3.8 6.2 5.8 Input Voltage (V) 5.4 5 4.6 4.2 3.8 Input Voltage (V) Input Voltage vs Efficiency Input Voltage vs Output Current 0.4 4 0.3 3 Output Voltage (V) Input Current (A) VF~3.6 0.0 0.2 2 0.1 1 VF~3.3 VF~3.6 VF~3.3 0.0 6.2 5.8 5.4 5 4.6 4.2 3.8 6.2 Input Voltage (V) Issue 1 - August 2007 © Zetex Semiconductors plc 2007 5.8 5.4 5 4.6 Input Voltage (V) 4.2 3.8 Input Voltage vs Output Voltage Input Voltage vs Input Current Figure 2 VF~3.6 0 Performance graphs for 1W design 3 www.zetex.com DN85 Ref. Value Package Part number Manufacturer Contact details Notes U1 N/A SOT23-6 ZXSC400E6 Zetex www.zetex.com LED Driver Q1 N/A SOT23 ZXTN25012EFL Zetex www.zetex.com Low sat NPN transistor D1 40V/1A SOT23 ZHCS1000 Zetex www.zetex.com 40V/1A Schottky diode L1 33H N/A 722065330 Wurth Elektronik www.we-online.com Isat=1.6A R1 30m⍀ 0805 Generic N/A 0805 1% R2 10⍀ 0805 Generic N/A 0805 5% R3 47⍀ 0805 Generic N/A 0805 5% C1 10F/10V 1210 Generic N/A X7R/X5R C2 100pF/10V 0805 Generic N/A COG/NPO C3 2.2uF/10V 1206 Generic N/A X7R/X5R optional Table 2 www.zetex.com Bill of materials for 3W LED 4 Issue 1 - August 2007 © Zetex Semiconductors plc 2007 DN85 Performance 0.8 100 0.7 Output Current (A) Efficiency (%) 90 80 70 60 VF~3.2 6 5.6 5.2 4.8 4.4 0.5 0.4 0.3 0.2 0.1 VF~3.5 50 6.4 0.6 VF~3.2 VF~3.5 0.0 4 6.4 6 Input Voltage (V) 5.6 5.2 4.8 4.4 4 Input Voltage (V) Input Voltage vs Efficiency Input Voltage vs Output Current 0.8 4 0.6 3 Output Voltage (V) Input Current (A) 0.7 0.5 0.4 2 0.3 0.2 1 VF~3.2 0.1 VF~3.5 VF~3.2 0.0 6.4 6 5.6 5.2 4.8 4.4 4 6.4 Input Voltage (V) Issue 1 - August 2007 © Zetex Semiconductors plc 2007 6 5.6 5.2 4.8 Input Voltage (V) 4.4 4 Input Voltage vs Output Voltage Input Voltage vs Input Current Figure 3 VF~3.5 0 Performance graphs for 3W design 5 www.zetex.com DN85 Definitions Product change Zetex Semiconductors reserves the right to alter, without notice, specifications, design, price or conditions of supply of any product or service. 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