ZXSC400EV3 User Guide Issue 4

ZXSC400EV3
ZXSC400EV3 USER GUIDE
DESCRIPTION
The ZXSC400 is voltage mode boost converter in
SOT23-6 package. Its low feedback voltage allows the
current in a chain of LEDs to be set and accurately
monitored with a single resistor with minimal losses.
The ZXSC400EV3 is configured as a boost converter
to drive a 1W LED from two NiCd/NiMH batteries.
FEATURES
•
Drives a 1W white LED at 350mA
•
Typical efficiency of 80%
APPLICATIONS
•
LED torches
•
High Power LED driving
ORDERING INFORMATION
ORDER NUMBER
ZXSC400EV3
Please note evaluation boards are subject to availability and qualified leads.
REFERENCE DESIGN
ZXSC400EV3 is configured to the reference design below. The target application is a 1W white LED Driving from
two NiCd/NiMH battery input for torches and high powered LED driving.
The supply voltage for ZXSC400EV3 is: VIN=3V ~ 1.8V.
For other reference designs or further applications information please refer to the ZXSC400 datasheet.
Schematic Diagram
L1
D1
22uH
ZHCS1000
VIN
Q1
ZXTN25012EFH
U1
1
3
C1
2
C2
ZXSC400
VCC
VDRIVE
STDN
ISENSE
GND
VFB
100uF/6V3
6
LED1
LXHL-PW01
4
5
100uF/6V3
R1
R2
22mohm
0.82ohm
GND
ZXSC400EV3
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ZXSC400EV3
Suggested components:
Ref
Value
Package
Part Number
Manufacturer
Notes
ZXSC400E6
ZXTN25012EFH
ZHCS1000
DO3316P-223
NPI31W220MTRF
Boost converter
Low sat NPN transistor
40V/1A Schottky diode
22uH/2.5A Inductor
U1
Q1
D1
L1
N/A
N/A
40V/1A
22uH/2.5A
SOT23-6
SOT23
SOT23
N/A
R1
22mΩ
0805
Zetex
Zetex
Zetex
Coilcraft
NIC Components
Generic
R2
0805
Generic
0805 5% tolerance
C1
0.82Ω
100µF/6V3
100uF/6V3/X5R
C2
100µF/6V3
1812
LED1
PCB
1W
N/A
Murata
NIC Components
Murata
NIC Components
Lumileds
Zetex
1812
GRM43SR60J107ME20L
NMC1812X5R107M6.3F
GRM43SR60J107ME20L
NMC1812X5R107M6.3F
LXHL-PW01
ZDB250R2
0805 5% tolerance
100uF/6V3/X5R
1W white LED emitter
Note: Components are continually being developed and improved. Please check each manufacturer’s data for
current products.
1W LED DRIVER
ZXSC400EV 3
a
L1
D2
VIN
D1
Q1
U1
3V m ax.
k
GND
C1
R1
R2
C2
ZD B250R3
C opy rightZetex PLC 2006
ZXSC400EV3 Set-up and Test
1. Connect VIN and GND to positive and zero volts of PSU supply respectively.
2. Set the PSU to 3V.
3. Turn on PSU.
4. The LED should illuminate and be regulated at 350mA.
5. Input current should measure between 0.5A ~ 0.6A - THIS IS A FUNCTIONAL EVAL. BOARD.
Layout considerations
PCB tracks should be kept as short as possible to minimise ground bounce, and the ground pin of the device
should be soldered directly to the ground plane. It is particularly important to mount the coil and the input/output
capacitors close to the device to minimise parasitic resistance and inductance, which will degrade efficiency. The
FB pin is a high impedance input, so PCB track lengths to this should also be kept as short as possible to reduce
noise pickup. Excess capacitance from the FB pin to ground should be avoided.
Manufacturer’s datasheets must be consulted regarding proper mounting and thermal management of the LED
device. The evaluation board is intended as a demonstration of the functionality of the driver circuitry, and is not
intended to represent a final solution for the OEM.
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ZXSC400EV3
PERFORMANCE
Increasing efficiency
On ZXSC400EV3, 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 performance graphs.
Graphs
100
VSTDN=VIN
LED Current (mA)
Efficiency (%)
90
400
VSTDN=VIN
ILED=350mA
R1=33mohms
80
70
R1=22mohms
60
50
3.0
2.8
2.6
2.4
2.2
2.0
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
4.0
VSTDN=VIN
3.8
800
R1=22mohms
R1=33mohms
600
400
3.0
LED Voltage (V)
Input Current (mA)
1000
VSTDN=VIN
2.8
2.6
2.4
2.2
2.0
1.8
Input Voltage (V)
R1=33mohms
3.6
3.4
R1=22mohms
3.2
3.0
3.0
2.8
2.6
2.4
2.2
2.0
1.8
Input Voltage (V)
Input Current vs Input Voltage
ZXSC400EV3
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LED Voltage vs Input Voltage
ZXSC400EV3
Definitions
Product change
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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
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circuit applications, under any circumstances.
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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 labeling can be reasonably expected to result in significant injury to the user.
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A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to
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ESD (Electrostatic discharge)
Semiconductor devices are susceptible to damage by ESD. Suitable precautions should be taken when handling and transporting devices. The
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can vary from immediate functional or parametric malfunction to degradation of function or performance in use over time. Devices suspected of
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Product status key:
“Preview”
“Active”
“Last time buy (LTB)”
“Not recommended for new designs”
“Obsolete”
Datasheet status key:
“Draft version”
Future device intended for production at some point. Samples may be available
Product status recommended for new designs
Device will be discontinued and last time buy period and delivery is in effect
Device is still in production to support existing designs and production
Production has been discontinued
This term denotes a very early datasheet version and contains highly provisional
information, which may change in any manner without notice.
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.
This term denotes an issued datasheet containing finalized specifications. However, changes to
specifications may occur, at any time and without notice.
“Provisional version”
“Issue”
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ZXSC400EV3
ISSUE 4 – January 2008
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