DN84

DN84
ZXSC400 Driving 3W high power LEDs
Ray Liu, Applications Engineer, Zetex Semiconductors
Description
This design note shows the ZXSC400 driving a single 3W LED. The input voltage ranges from 1.8V
to 3.6V with constant output current of 700mA down to 2.6V with an overall 80% of efficiency.
Figure 1 shows typical constant current solution with ZXSC400 driving one 3W LED. The input
voltage range allows the use of two alkaline batteries or one Lithium Ion cell (CR123A) for
portable flashlight applications.
Q1 and Q2 forms a pseudo Darlington pair which provide enough current gain for a switching
current up to 1.5A. In order to provide better switch off performance, a Schottky diode, D2, is used
to drain the base current from the base of Q1 directly. In order to achieve higher efficiency, current
monitor U2 is used to provide a low voltage drop LED current sensing through the low ohmic
resistor, R2. The LED current is converted to 300mV feedback voltage through R3.
D1
L1
VIN = 1.8V to 3V
R2
U2
VSENSE+
Q2
C1
R4
VSENSE-
IOUT
ZXCT1009
Q1
C2
U1
C1
VCC
VDRIVE
Stdn
ISENSE
GND
VFB
D2
R6
D1
R5
ZXSC400
C3
R3
R1
Figure 1
Issue 1 - August 2007
© Zetex Semiconductors plc 2007
Schematic diagram
1
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DN84
Ref.
Value
U1
Part number
Manufacturer
Comments
ZXSC400E6
Zetex
LED driver in SOT23-6
U2
ZXCT1009
Zetex
Current monitor in SOT23
Q1
ZXTN25012EFH
Zetex
Low sat NPN in SOT23
Q2
ZXTN25012EFL
Zetex
Low sat NPN in SOT23
D1
ZHCS2000
Zetex
2A Schottky in SOT23
D2
ZHCS400
Zetex
400mA Schottky
L1
15␮H
744 561 15
Wurth Electronik
ISAT = 3A DCR=60m⍀
R1
20m⍀ 1%
Generic
Generic
0805 size low ohmic
R2
50m⍀ 1%
Generic
Generic
0805 size low ohmic
R3
820⍀ 1%
Generic
Generic
0805 size
R4
82⍀ 5%
Generic
Generic
0805 size
R5
4.7⍀ 5%
Generic
Generic
0805 size
R6
10⍀ 5%
Generic
Generic
0805 size
C1
22␮F 10V 10%
Generic
Generic
1206 size X7R/X5R
C2
4.7␮F 10V 10%
Generic
Generic
1206 size X7R/X5R
C3
0.22␮F 16V
10%
Generic
Generic
C4
330pF/10V
Generic
Generic
0805 size
Table 1
www.zetex.com
Bill of materials
2
Issue 1 - August 2007
© Zetex Semiconductors plc 2007
DN84
Typical operating characteristics
(For typical application circuit where Tamb = 25°C unless otherwise stated)
90
0.8
Output Current (A)
1.0
Efficiency (%)
100
80
70
60
50
0.6
0.4
0.2
0.0
3
2.8
2.6
2.4
2.2
2
1.8
3
2.8
2.6
Input Voltage (V)
Input Voltage vs Efficiency
2.2
2
1.8
Input Voltage vs Output Current
1.6
4
1.2
3
Output Voltage (V)
Input Current (A)
2.4
Input Voltage (V)
0.8
0.4
2
1
0
0.0
3
2.8
2.6
2.4
2.2
2
3
1.8
2.8
2.6
Input Voltage vs Input Current
Figure 2
Issue 1 - August 2007
© Zetex Semiconductors plc 2007
2.4
2.2
2
1.8
Input Voltage (V)
Input Voltage (V)
Input Voltage vs Output Voltage
Performance graphs
3
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DN84
Definitions
Product change
Zetex Semiconductors reserves the right to alter, without notice, specifications, design, price or conditions of supply of any product or
service. Customers are solely responsible for obtaining the latest relevant information before placing orders.
Applications disclaimer
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
arising from such use or otherwise. Zetex does not assume any legal responsibility or will not be held legally liable (whether in contract,
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.
Life support
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.
Reproduction
The product specifications contained in this publication are 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 contract or be regarded as a
representation relating to the products or services concerned.
Terms and Conditions
All products are sold subjects to Zetex’ terms and conditions of sale, and this disclaimer (save in the event of a conflict between the two
when the terms of the contract shall prevail) according to region, supplied at the time of order acknowledgement.
For the latest information on technology, delivery terms and conditions and prices, please contact your nearest Zetex sales office .
Quality of product
Zetex is an ISO 9001 and TS16949 certified semiconductor manufacturer.
To ensure quality of service and products we strongly advise the purchase of parts directly from Zetex Semiconductors or one of our
regionally authorized distributors. For a complete listing of authorized distributors please visit: www.zetex.com/salesnetwork
Zetex Semiconductors does not warrant or accept any liability whatsoever in respect of any parts purchased through unauthorized sales channels.
ESD (Electrostatic discharge)
Semiconductor devices are susceptible to damage by ESD. Suitable precautions should be taken when handling and transporting devices.
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.
Green compliance
Zetex Semiconductors is committed to environmental excellence in all aspects of its operations which includes meeting or exceeding
regulatory requirements with respect to the use of hazardous substances. Numerous successful programs have been implemented to
reduce the use of hazardous substances and/or emissions.
All Zetex components are compliant with the RoHS directive, and through this it is supporting its customers in their compliance with
WEEE and ELV directives.
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
specifications may occur, at any time and without notice.
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USA
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Hong Kong
Zetex Semiconductors plc
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Oldham, OL9 9LL
United Kingdom
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]
© 2007 Published by Zetex Semiconductors plc
www.zetex.com
4
Issue 1 - August 2007
© Zetex Semiconductors plc 2007
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