ZXLD1360EV8 User Guide Issue 3

ZXLD1360EV8 EVALUATION BOARD USER GUIDE
DESCRIPTION
The ZXLD1360EV8, Figure 1, is a double sided evaluation board for the ZXLD1360 LED driver with internal
switch. The evaluation board is preset to drive a 660mA into a single LED, or an external choice of LEDs. The
number of externally connected LEDs depends on the forward voltage of the LEDs connected.
The LED fitted on this evaluation board is supplied by Cree Inc. For further information on the Cree range of
LEDs, please visit their website at: www.cree.com
The operating voltage is nominally 30 volts, but can be reduced to 7 volts. The 33uH inductor used in the circuit is
based on this nominal supply, which should be connected across +Vin and Gnd pins. Note: The evaluation
board does not have reverse battery protection. The nominal current for the evaluation board is set at 660mA
with a 0R15 sense resistor, R1.
Alternative LEDs can be connected using the terminals marked LED A and LED K but the onboard LED should
be disconnected first by removing J3.
Terminal Adj provides a connection point for DC or PWM dimming and shutdown.
The evaluation board includes a thermal protection circuit to ensure the LED is not over-driven under normal use.
This circuit can be disabled by removing J7
Warning: At 30V nominal operation with 660mA output, the LED will be hot and very bright
Figure 1: ZXLD1360EV8 evaluation board
Issue 3 – May 2009
© Diodes Incorporated, 2008
www.diodes.com
ZXLD1360EV8
ZXLD1360 DEVICE DESCRIPTION
The ZXLD1360 is a continuous mode inductive driver in a TSOT23-5 package, for driving one or more seriesconnected LEDs efficiently from a voltage source higher than the LED voltage. The device includes the output
switch and a current sense circuit, which requires an external sense resistor to set the nominal current up to
1000mA.
ZXLD1360 DEVICE FEATURES
•
Drives one or more series-connected LEDs
•
LEDs up to 1000mA.
•
Internal 30V switch.
•
Wide input voltage: 7V to 30V.
•
Inherent open circuit LED protection.
•
Brightness control using DC or PWM.
•
Internal PWM filter.
DEVICE APPLICATIONS
•
LED flashlights.
•
High Power LED driving.
•
Low-voltage halogen replacement LEDs.
•
Automotive lighting.
•
Illuminated signs.
ZXLD1360 Device Packages, Pin and Definitions
TSOT23-5 pack
ZXLD1360 Device Pin Definition
Name
Pin No
LX
1
GND
2
ADJ
3
ISENSE
4
VIN
5
Description
Drain of NDMOS switch.
Ground (0V).
Internal voltage ref. pin (1.25V) :
•
Leave floating for normal operation.
•
Connect to GND to turn off output current.
•
Drive with DC voltage (0.3V to 1.25V) or with PWM signal to adjust
output current or....
•
Connect a capacitor from this pin to ground to set soft-start time.
Connect a sense resistor, Rs, from the ADJ pin to VIN to sense the nominal
output current. Nominal Iout = 0.1/ R1
Input voltage: 7V to 30V. Decouple to ground with a 2U2F or higher ceramic
capacitor.
ORDERING INFORMATION
EVALBOARD ORDER NUMBER
ZXLD1360EV8
DEVICE ORDER NUMBER
ZXLD1360E5TA
Please note: Evaluation boards are subject to
availability and qualified sales leads.
Issue 3 – May 2009
www.diodes.com
© Diodes Incorporated 2008
2
ZXLD1360EV8
ZXLD1360EV8 EVALUATION BOARD
REFERENCE DESIGN
The ZXLD1360EV8 is configured to the reference design in Figure 2. The target application is a driver for torches
or other high powered LED applications.
The operating voltage is a nominal 30V.The nominal current is set at 660mA with a 0R15 sense resistor, R1 and
the circuit operates in continuous mode at 300kHz approximately , with a 33uH inductor.
An accurate way of determining the current is to measure the voltage on the sense resistor. A 10K resistor and a
1uF capacitor can be used to form a low pass filter and the voltage across the capacitor represents a more stable
dc reading of current . 100mV represents 1 Amp when using a 0.1Ω sense resistor.
The ADJ pin has a low pass filter within the 1360 chip to provide some decoupling and soft a start but the
external capacitor C1 (100nF) is used to provide additional decoupling to reduce any high frequency noise as
well as providing an extra amount of soft start.
Both DC and PWM dimming can be achieved by driving the ADJ pin. For DC dimming, the ADJ pin may be
driven between 0.3V and 1.25V. Driving the ADJ pin below 0.2V will shutdown the output current. For PWM
dimming, an external open-collector NPN transistor or open-drain N-channel MOSFET can be used to drive the
ADJ pin. The PWM frequency can be low, around 100Hz to 1kHz, or high between 10kHz to 50kHz.
For low frequency PWM C1 should be removed on the evaluation board to give a more accurate duty cycle .
Shorting R2 will connect the test pin ADJ to device pin ADJ if needed.
The soft-start time will be nominally 0.5ms without capacitor C1. Adding C1 will increase the soft start time by
approximately 0.5ms/nF
For other reference designs or further applications information, please refer to the ZXLD1360 datasheet.
Schematic Diagram
`
R1
0R15
JP1
LED 1
Vin
LED A
R2 1k
ADJ
Thermally
connected
R4
4k7
C2
2.2uF
C3
5
Vin
R3
1k
JP2
3
ZXLD 1360
ADJ
LX
100nF
D1
4
V Sense
1
L1 33 uH
LED K
Q1
D2
1.24V
GND
2
R5
10 k NTC
Thermistor
C1
100 nF
GND
Figure 2: Schematic for the evaluation board ZXLD1360EV8
Issue 3 – May 2009
www.diodes.com
© Diodes Incorporated 2008
3
ZXLD1360EV8
ZXLD1360 Operation
In normal operation, when voltage is applied at +Vin, the ZXLD1360 internal NDMOS switch is turned on. Current
starts to flow through sense resistor R1, inductor L1, and the LED. The current ramps up linearly, and the ramp
rate is determined by the input voltage +Vin and the inductor L1. This rising current produces a voltage ramp
across R1. The internal circuit of the ZXLD1360 senses the voltage across R1 and applies a proportional voltage
to the input of the internal comparator. When this voltage reaches an internally set upper threshold, the NDMOS
switch is turned off. The inductor current continues to flow through R1, L1, the LED and the schottky diode D1,
and back to the supply rail, but it decays, with the rate of decay determined by the forward voltage drop of the
LEDs and the schottky diode. This decaying current produces a falling voltage at R1, which is sensed by the
ZXLD1360. A voltage proportional to the sense voltage across R1 is applied at the input of the internal
comparator. When this voltage falls to the internally set lower threshold, the NDMOS switch is turned on again.
This switch-on-and-off cycle continues to provide the average LED current set by the sense resistor R1. Please
refer to the datasheets for the threshold limits, ZXLD1360 internal circuits, electrical characteristics and
parameters.
To prevent overheating of the LED, a 10K thermistor (R5) provides feedback of the LED temperature to the base
of Q1 which is held at 1.23 volts by D2 R3 and R4 at ambient 25°C. The emitter is above the ADJ voltage of the
1360 and so if full current of 1 amp is programmed by the R sense resistor the LED current reduces to around
500mA if no additional heat-sinking is provided to the eval board. The voltage on the ADJ pin is 800mV approx
when the LED is hot. This function may be disabled by removing jumper link J7.
ZXLD1360EV8 Component list
Ref
R1
R2, R3
R4
R5
C1, C3
Value
0R15
1K
4k7
10K
100nF, 50V
Package
0805
0805
0805
1206
0805
C2
L1
D1
D2
U1
LED1
Q1
2u2F 50V
33uH
40V, 3A
1.23V
ZXLD1360
LED
PNP
1206
SOT-23
TSOT23-5
SOT- 23
Part Number
B57621C103J62
NMC0805X7R104K50TRPF
GRM21BR71H104KA01L
GRM31CR71H225KA88L
NPIS64D330MTRF
B340B
ZRA124F01TA
ZXLD1360E5TA
XREWHT-L1-WC-P2-01
BCW68H
Manufacturer
Generic
Generic
Generic
Epcos
NIC Comps
MURATA
MURATA
NIC Comps
Diodes Zetex
Diodes Zetex
Diodes Zetex
Cree
Diodes Zetex
Notes
5%
1%
1%
NTC Thermistor
X7R
X7R
33uH, 1.1A rms
Schottky diode
Voltage ref
DC-DC converter
Note: The component part numbers are correct at the time of publication. Zetex Semiconductors Plc reserves the
right to substitute other parts where necessary, without further notification.
The solder pad on the underside of the LED is connected to a heat-dissipating copper plane on the top and
bottom layers which is electrically isolated from all other connections on the board.
Warning: At 30V operation with 1000mA output, the heatsink temperature rises to 80°C from ambient
after 30 minutes of operation.
Issue 3 – May 2009
www.diodes.com
© Diodes Incorporated 2008
4
ZXLD1360EV8
Figure 3: Component layout
ZXLD1360EV8 Connection Point Definition
Name
Description
Vin
Positive supply voltage.
Gnd
Supply Ground (0V).
Adj
LED A
LED K
Internal voltage ref. pin (1.25). This pin can be used to achieve dimming and soft-start,
and for switching the output current off.
•
Leave floating for normal operation.
•
See 'Other Features' section to achieve dimming, and soft-start and for switching
the output current off.
LED A connects to the ANODE of LED1, and is the external LED anode connection
point. Disconnect the jumper JP1 when driving an external load.
LED K connects to the CATHODE of LED1, and is the external LED cathode
ZXLD1360EV8 Basic operation at full voltage
1.
2.
3.
Connect Vin and Gnd .
Warning: The board does not feature reverse battery/supply protection.
Set the PSU to 30V
Turn on the PSU and the LED will illuminate and the current should be approximately 660mA.
Warning: Do not stare at the LED directly.
Issue 3 – May 2009
www.diodes.com
© Diodes Incorporated 2008
5
ZXLD1360EV8
Circuit features (Remove power whilst changing components!)
Soft-start
1.
Fit a capacitor at C1 to alter the rise-time of the adjust pin at start-up. The output impedance is 200K so
200,000Ω x C1 (farads) is the time constant to reach 66% of the maximum output current
Switching the output current off
1.
Short the Adj pin to Gnd and the LED current will go to zero. Releasing this pin will create a soft-start
power-up sequence.
Changing the LED current
1.
2.
Remove R1.
Calculate and fit a new sense resistor, R1, the value of which is based on the required LED current
without dimming. R1 can be calculated using following equation :
R1 = 0.1V/IOUT
where
IOUT = the LED current.
R1 = the sense resistor value in ohms.
0.1V is the nominal sense voltage with ‘Adj’ open circuit or set to 1.25V.
Using external LEDs or loads
1.
2.
Switch off the power supply.
Connect external LEDs across test pins ‘LED A’ and ‘LED K’. ‘LED A’ is the LEDs anode connection
point and ‘LED K’ is the LEDs cathode connection point. The number of external LEDs that can be
connected depends on their operating power and forward voltage drop. For an external load other than
LEDs, the positive terminal of the load should be connected to test pin ‘LED A’ and the negative terminal
of the load should be connected to test pin ‘LED K’. The onboard LED should be disconnected by
removing J3.
PERFORMANCE
The system efficiency depends on the sense resistor, supply voltage, switching inductor and the number of LEDs
With a 30V supply the switching frequency is typically 200kHz and theefficiency level is >85% .
Issue 3 – May 2009
www.diodes.com
© Diodes Incorporated 2008
6
ZXLD1360EV8
INTENTIONALLY BLANK
Issue 3 – May 2009
www.diodes.com
© Diodes Incorporated 2008
7
ZXLD1360EV8
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
Kustermannpark
Balanstraße 59,
D-81541 München
7F, No. 50,
Min Chuan Road
Hsin-Tien
Rm. 606, No.1158
Changning Road
Shanghai, China
Room A1103-04,
ANLIAN Plaza, #4018
Jintian Road
6 Floor, Changhwa B/D,
1005-5 Yeongtong-dong,
Yeongtong-gu, Suwon-si,
Tel: (+1) 805 446 4800
Fax: (+1) 805 446 4850
Germany
Tel: (+49) 894 549 490
Fax: (+49) 894 549 4949
Taipei, Taiwan
Tel: (+886) 289 146 000
Fax: (+886) 289 146 639
Tel: (+86) 215 241 4882
Fax (+86) 215 241 4891
Futian CBD,
Shenzhen, China
Tel: (+86) 755 882 849 88
Fax: (+86) 755 882 849 99
Gyeonggi-do, Korea 443-813
Tel: (+82) 312 731 884
Fax: (+82) 312 731 885
Issue 3 – May 2009
www.diodes.com
© Diodes Incorporated 2008
8