ZXLD381EV1 User Guide Issue 2

ZXLD381EV1 USER GUIDE
Description
The ZXLD381 is a single or multi cell LED driver
designed for applications requiring step-up
voltage conversion from a very low input voltage
and on/off enable control. The IC generates
constant current pulses that are ideal for driving
single or multiple LEDs over a wide range of
operating voltages.
The IC can start up under full load and operates
down to an input voltage of below 0.9V.
The ZXLD381 is offered in the space saving
SOT23-3 package or in die form, offering an
excellent cost versus performance solution for
single cell LED driving applications.
The ZXLD381 uses a PFM control technique to
drive an internal switching transistor which
exhibits a low saturation resistance. This ensures
high efficiency, even for input voltages as low as
1.0V.
Features
Applications
•
•
•
•
•
•
•
• LED flashlights and torches
• LED backlights
• White LED driver
85% Efficiency
User adjustable output current
Single cell operation (0.9V minimum)
Low saturation voltage switching transistor
SOT23-3 package
Available also in Die form
Simple Application circuit
Ordering information
Typical application circuit
L1
3
Vin
ZXLD381
Vout
2
GND
Please note evaluation
boards are subject to
availability and qualified
leads.
4u7
SW1
1
ORDER NUMBER
ZXLD381EV1
ZXLD381
Batt
LED1
LED2
LED3
GND
Issue 2 - June 2009
© Diodes Incorporated, 2009
www.diodes.com
ZXLD381EV1
Reference design
ZXLD381EV1 evaluation board is designed to drive up to 3 white LEDs in parallel. The target application is
single cell flashlights and torches.
This board is designed to accept a single AAA cell as the voltage source. Please note that the board does not
have reverse polarity protection, so the battery must be fitted correctly.
The circuit is switched on using the momentary push button and goes off when the button is released.
The design demonstrates the simplicity possible with this device: the capacitor C1 may be omitted if the battery is
close to the device but is needed otherwise.
The evaluation board is fitted with three T1¼ white LEDs, and to use these, the jumper P1 must be fitted.
External LEDs may be connected via CON1 and CON2, marked LED +ve and LED –ve respectively. In this
case the jumper must be removed.
For other reference designs or further applications information please refer to the ZXLD381 datasheet.
Schematic diagram
L1
4u7
SW1
3
Batt
Batt
2
GND
ZXLD381
Vout
LED+ve
1
C1
4.7uF
1
+2
Vin
P1
2
1
ZXLD381
Header 2
LED1
LED2
LED3
LED-ve
GND
Issue 2 - June 2009
www.diodes.com
© Diodes Incorporated, 2009
2
ZXLD381EV1
Components list
Ref
Value
U1
L1
C1
LED1,2,3
LED Driver
4.7uH
4.7uF 25V X7R
5mm White LED
Package
SOT23-3
ME3220
Part Number
Manufacturer
ZXLD381FHTA
ME3220-472MLB
C1206C475K3RAC
[email protected]
Zetex
Coilcraft
Kemet
(generic)
Contact Details
www.zetex.com
www.coilcraft.com
www.kemet.com
Performance graphs
Input Current v Batt Voltage
200
180
160
Batt ma
140
120
100
Iin
80
60
40
20
0
0.9
1
1.1
1.2
1.3
1.4
1.5
Batt Volts
LED Current v Batt Voltage
45
40
35
LED mA
30
25
20
15
10
5
0
0.9
1
1.1
1.2
1.3
1.4
1.5
Batt Volts
Issue 2 - June 2009
www.diodes.com
© Diodes Incorporated, 2009
3
ZXLD381EV1
% efficiency v Batt Voltage
100
90
80
70
%
60
50
40
30
20
10
0
0.9
1
1.1
1.2
1.3
1.4
1.5
Batt Volts
ZXLD381EV1 operation
Component layout diagram
ZXLD381EV1 set-up and test
1.
2.
3.
4.
5.
6.
7.
Preset the PSU to 1.5V with a current limit of around 200mA.
Close the link P1.
Connect Batt +ve and Batt -ve to the positive and zero volts respectively, of a battery or power supply.
Ensure that the connections are made correctly, as the board is not reverse polarity protected.
Turn on the PSU.
The LEDs should illuminate.
The input current should measure between 120mA - 160mA.
Turn off the PSU
Layout considerations
PCB tracks should be kept as short as possible to minimize ground bounce. It is particularly important to mount
the coil and the input/output capacitors close to the device to minimize parasitic resistance and inductance, which
will degrade efficiency.
Issue 2 - June 2009
www.diodes.com
© Diodes Incorporated, 2009
4
ZXLD381EV1
Intentionally blank
Issue 2 - June 2009
www.diodes.com
© Diodes Incorporated, 2009
5
ZXLD381EV1
Intentionally blank
Issue 2 - June 2009
www.diodes.com
© Diodes Incorporated, 2009
6
ZXLD381EV1
Intentionally blank
Issue 2 - June 2009
www.diodes.com
© Diodes Incorporated, 2009
7
ZXLD381EV1
IMPORTANT NOTICE
DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARD TO THIS
DOCUMENT, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
FITNESS FOR A PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION).
Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements,
corrections or other changes without further notice to this document and any product described herein. Diodes Incorporated
does not assume any liability arising out of the application or use of this document or any product described herein; neither
does Diodes Incorporated convey any license under its patent or trademark rights, nor the rights of others. Any Customer
or user of this document or products described herein in such applications shall assume all risks of such use and will agree
to hold Diodes Incorporated and all the companies whose products are represented on Diodes Incorporated website,
harmless against all damages.
Diodes Incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through
unauthorized sales channels. Should Customers purchase or use Diodes Incorporated products for any unintended or
unauthorized application, Customers shall indemnify and hold Diodes Incorporated and its representatives harmless
against all claims, damages, expenses, and attorney fees arising out of, directly or indirectly, any claim of personal injury or
death associated with such unintended or unauthorized application.
Products described herein may be covered by one or more United States, international or foreign patents pending. Product
names and markings noted herein may also be covered by one or more United States, international or foreign trademarks.
LIFE SUPPORT
Diodes Incorporated 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 Diodes Incorporated. 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 labeling 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
be expected to cause the failure of the life support device or to affect its safety or effectiveness.
Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support
devices or systems, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related
requirements concerning their products and any use of Diodes Incorporated products in such safety-critical, life support
devices or systems, notwithstanding any devices- or systems-related information or support that may be provided by
Diodes Incorporated. Further, Customers must fully indemnify Diodes Incorporated and its representatives against any
damages arising out of the use of Diodes Incorporated products in such safety-critical, life support devices or systems.
Copyright © 2009, Diodes Incorporated
www.diodes.com
Sales offices
The Americas
Europe
Taiwan
Shanghai
Shenzhen
Korea
3050 E. Hillcrest Drive
Westlake Village,
CA 91362-3154
Tel: (+1) 805 446 4800
Fax: (+1) 805 446 4850
Kustermannpark
Balanstraße 59,
D-81541 München
Germany
Tel: (+49) 894 549 490
7F, No. 50,
Min Chuan Road
Hsin-Tien
Taipei, Taiwan
Tel: (+886) 289 146 000
Rm. 606, No.1158
Changning Road
Shanghai, China
Tel: (+86) 215 241 4882
Fax (+86) 215 241 4891
Room A1103-04,
ANLIAN Plaza, #4018
Jintian Road
Futian CBD,
Shenzhen, China
6 Floor, Changhwa B/D,
1005-5 Yeongtong-dong,
Yeongtong-gu, Suwon-si,
Gyeonggi-do, Korea 443-813
Tel: (+82) 312 731 884
Fax: (+49) 894 549 4949
Fax: (+886) 289 146 639
Tel: (+86) 755 882 849 88
Fax: (+86) 755 882 849 99
Fax: (+82) 312 731 885
Issue 2 - June 2009
www.diodes.com
© Diodes Incorporated, 2009
8