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
D1
22uH
ZHCS1000
VIN
Q1
LED1
FMMT617
U1
ZXSC400
C1
100uF/6V3
VCC
VDRIVE
STDN
ISENSE
GND
LXHL-PW01
C2
VFB
100uF/6V3
R1
R2
22mohm
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
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
LXHL-PW01
www.lumileds.com 1W white LED
emitter
LED1 1W
N/A
DO3316P-223
Table 1
Issue 1 - May 2005
© Zetex Semiconductors plc 2005
Lumileds
Bill of materials
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 improved efficiency R1 can be changed to a 33mΩ
resistor but LED current will not be regulated below 2V. See Figure 2, Performance graphs.
400
VSTDN=VIN
ILED=350mA
90
LED Current (mA)
Efficiency (%)
100
R1=33mohms
80
70
R1=22mohms
60
50
3.0
2.8
2.6
2.4
2.2
2.0
VSTDN=VIN
380
R1=22mohms
360
340
R1=33mohms
320
300
3.0
1.8
2.8
2.6
2.4
2.2
2.0
1.8
Input voltage (V)
Input Voltage (V)
Efficiency vs Input Voltage
LED Current vs Input Voltage
1000
800
VSTDN=VIN
R1=22mohms
600
400
3.0
LED Voltage (V)
Input Current (mA)
4.0
VSTDN=VIN
R1=33mohms
2.8
2.6
2.4
2.2
2.0
3.8
R1=33mohms
3.6
3.4
R1=22mohms
3.2
3.0
3.0
1.8
2.8
Input Voltage (V)
Input Current vs Input Voltage
Figure 2
2.6
2.4
2.2
2.0
1.8
Input Voltage (V)
LED Voltage vs Input Voltage
Performance graphs
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
europe.sales@zetex.com
Telephone: (1) 631 360 2222
Fax: (1) 631 360 8222
usa.sales@zetex.com
Telephone: (852) 26100 611
Fax: (852) 24250 494
asia.sales@zetex.com
Telephone (44) 161 622 4444
Fax: (44) 161 622 4446
hq@zetex.com
These offices are supported by agents and distributors in major countries world-wide.
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
2
Issue 1 - May 2005
© Zetex Semiconductors plc 2005