DN85

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
47␮H
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
4.7␮F/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
33␮H
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
10␮F/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
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DN85
Definitions
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The circuits in this design/application note are offered as design ideas. It is the responsibility of the user to ensure that the circuit is fit for
the user’s application and meets with the user’s requirements. No representation or warranty is given and no liability whatsoever is
assumed by Zetex with respect to the accuracy or use of such information, or infringement of patents or other intellectual property rights
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tort (including negligence), breach of statutory duty, restriction or otherwise) for any damages, loss of profit, business, contract,
opportunity or consequential loss in the use of these circuit applications, under any circumstances.
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Zetex products are specifically not authorized for use as critical components in life support devices or systems without the express written
approval of the Chief Executive Officer of Zetex Semiconductors plc. As used herein:
A. Life support devices or systems are devices or systems which:
1. are intended to implant into the body
or
2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the
labelling can be reasonably expected to result in significant injury to the user.
B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to
cause the failure of the life support device or to affect its safety or effectiveness.
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ESD (Electrostatic discharge)
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The possible damage to devices depends on the circumstances of the handling and transporting, and the nature of the device. The extent
of damage can vary from immediate functional or parametric malfunction to degradation of function or performance in use over time.
Devices suspected of being affected should be replaced.
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Product status key:
“Preview”
Future device intended for production at some point. Samples may be available
“Active”
Product status recommended for new designs
“Last time buy (LTB)”
Device will be discontinued and last time buy period and delivery is in effect
“Not recommended for new designs” Device is still in production to support existing designs and production
“Obsolete”
Production has been discontinued
Datasheet status key:
“Draft version”
This term denotes a very early datasheet version and contains highly provisional information, which
may change in any manner without notice.
“Provisional version”
This term denotes a pre-release datasheet. It provides a clear indication of anticipated performance.
However, changes to the test conditions and specifications may occur, at any time and without notice.
“Issue”
This term denotes an issued datasheet containing finalized specifications. However, changes to
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© 2007 Published by Zetex Semiconductors plc
www.zetex.com
6
Issue 1 - August 2007
© Zetex Semiconductors plc 2007
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