Zetex Semiconductors PLC Computer Hardware ZXLD1362EV3 User Manual

ZXLD1362EV3 USER GUIDE  
DESCRIPTION  
The ZXLD1362EV3, Figure 1, is a PCB constructed using an aluminium base for evaluating the ZXLD1362 LED  
driver with internal switch [1]. The evaluation board can be used to drive an external choice of LEDs; the total forward  
voltage across the LEDs depending on the number and type connected.  
The operating voltage is nominally higher than 30V for the external LEDs, and can be raised to 60V maximum, which  
will reduce the supply current. Please refer to the Zetex ZXLD1360 and ZXLD1350 products for applications requiring  
input voltages lower than 30V.  
The nominal current for the evaluation board is set at 700mA with a 0.15Ω sense resistor, R1.  
The 68uH inductor used in the circuit is based on a 30V nominal supply, which should be connected across +VIN and  
GND pins.  
Note: The evaluation board does not have reverse polarity protection. It is fitted with a 2.1mm DC power plug with  
positive to the centre pole.  
Test point ADJ provides a connection point for DC or PWM dimming and shutdown.  
Warning: with 700mA output, the connected LED will be hot and very bright  
Figure 1: ZXLD1362EV3 evaluation board  
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ZXLD1362EV3 EVALUATION BOARD  
REFERENCE DESIGN  
The ZXLD1362EV3 is configured to the reference design in Figure 2. The target application is a driver for one or  
more series-connected LEDs for luminaires in both commercial and automotive applications.  
The maximum operating voltage is 60V, and the nominal current is set at 700mA with a 0.15Ω sense resistor R1. The  
device operates in continuous mode at approximately 150 kHz, with a 68uH inductor.  
An accurate way of determining the current, avoiding the need to insert an ammeter in the current path, 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. Using this method, 100mV represents  
0.7 Amp when using a 0.15sense resistor.  
The ADJ pin connects to a low pass filter within the ZXLD1362 chip to provide some decoupling, but the external  
capacitor C2 (100nF) is used to provide additional decoupling to reduce any high frequency noise as well as  
enabling the soft start function.  
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 shut down 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 1 kHz, or high between 10 kHz to 50 kHz.  
For low frequency, PWM capacitor C2 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 external capacitor C2 on the ADJ pin sets the soft start time. The amount of soft start time achievable is  
approximately 0.2ms/nF.  
For other reference designs or further applications information, please refer to the ZXLD1362 datasheet.  
Schematic Diagram  
Figure 2 shows the schematic for the ZXLD1362EV3 evaluation board.  
LED A  
R1  
Vin  
4
5
C3  
Vin  
V sense  
D1  
C4  
C1  
L1  
ADJ  
1
R2  
3
ADJ  
LX  
ZXLD1362  
LED K  
GND  
C2  
GND  
Figure 2: Schematic for the evaluation board ZXLD1362EV3  
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ZXLD1362 Operation  
In normal operation, when voltage is applied at +VIN, the ZXLD1362 internal NDMOS switch is turned on. Current  
starts to flow through sense resistor R1, inductor L1, and the LEDs. 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 ZXLD1362 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 LEDs, 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 ZXLD1362. 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 an average  
current (set by the sense resistor R1) to the LEDs, . Please refer to the datasheet [1] for the threshold limits,  
ZXLD1362 internal circuits, electrical characteristics and parameters.  
ZXLD1362EV1 Evaluation Board - BOM  
Ref  
R1  
R2  
C1  
Value  
0.15R  
1k  
Package  
0805  
0805  
SMD  
0805  
1206  
-
SMC  
Part Number  
CRL1220 R15TD  
Manufacturer  
Notes  
5%, 200ppm  
-
Electrolytic - 20%  
20%  
Tyco  
-
Generic  
10uF 100V  
NACEW100M1006.3x8TR13F  
NMC0805X7R104K100TRPLPF  
NMC1206X7R104K100TRPLP3KF  
NPIS24H680MTRF  
NIC  
NIC  
NIC  
NIC  
IR  
C2,C4 100nF, 100V  
C3  
L1  
D1  
U1  
100nF  
68uH  
100V, 3A  
ZXLD1362  
68uH/1.5A rms  
Schottky diode  
DC-DC converter  
30BQ100PBF  
ZXLD1362E5TA  
TSOT23-5  
Zetex  
The aluminium PCB guarantees a good thermal dissipation for the ZXLD1362 device, which can produce up to 1 watt  
of heat under maximum load conditions. Other sources of heat are the Schottky diode, the inductor and the sense  
resistor. Care must be taken in their placement.  
Warning: At 60V operation with 700mA output, the board temperature rises by around 50C from ambient  
after 30 minutes of operation.  
Figure 3: Component layout and circuit board view  
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ZXLD1362EV3 Connection Point Definition  
Name  
+VIN  
GND  
Description  
Positive supply voltage.  
Supply Ground (0V).  
ADJ  
Internal voltage ref. pin (1.25V). This pin can be used to achieve dimming and soft-start,  
and for switching the output current off.  
Leave floating for normal operation.  
See 'Circuit Features' section to achieve dimming, soft-start and for switching the  
output current off.  
LED A  
LED K  
LED A connects to the external LED anode  
LED K connects to the external LED cathode  
ZXDL1362EV3 Basic operation at full voltage  
1. Connect external LEDs across test pins ‘LED A’ (anode) and ‘LED K’ (cathode). The number of external  
LEDs that can be connected depends on their operating power and forward voltage drop, but typically 16 x  
3.4V LEDs can be connected using a 60V rail. For an external load other than LEDs, the positive terminal of  
the load should be connected the anode and the negative to the cathode.  
2. Connect VIN and GND.  
Warning: The board does not feature reverse battery/supply protection.  
3. Set the PSU to the desired input voltage (usually between 30V and 60V)  
4. Turn on the PSU. The external LEDs will illuminate and the current should be approximately 700mA.  
Warning: Do not stare at the LEDs directly.  
Circuit features  
N.B. Remove power whilst changing components!  
Soft-start  
1. The evaluation board is fitted with capacitor C2, which performs the soft start function by slowing the rise  
time of the adjust pin at start-up. The pin output impedance is 50K so CxR is the time constant to reach 66%  
of output current.  
PWM  
1. Remove the soft start capacitor C2  
2. Refer to the datasheet for how to perform PWM  
Switching off the output current  
3. Shorting the ADJ pin to GND will cause the LED current to go to zero. Releasing this pin will switch on the  
system (creating a soft-start power up sequence if the C2 capacitor is used).  
Changing the LED current  
1. Remove R1  
2. 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 = 0.1(V / 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.  
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PERFORMANCE  
The system efficiency depends on the sense resistor, supply voltage, switching inductor, and the number of LEDs.  
With a 60V supply and 15 LEDs, the switching frequency is typically 200 kHz and efficiency levels >90% are  
achievable.  
Visit our website www.zetex.com to find useful tools for circuit design and simulation.  
REFERENCE  
[1] ZXLD1362 Datasheet – www.zetex.com  
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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 labeling can be reasonably expected to result in significant injury to the user.  
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.  
B.  
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”  
“Active”  
Future device intended for production at some point. Samples may be available  
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”  
“Issue”  
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.  
Europe  
Americas  
Asia Pacific  
Corporate Headquarters  
Zetex GmbH  
Kustermann-park  
Balanstraße 59  
D-81541 München  
Germany  
Zetex Inc  
Zetex (Asia Ltd)  
Zetex Semiconductors plc  
Zetex Technology Park, Chadderton  
Oldham, OL9 9LL  
700 Veterans Memorial Highway  
Hauppauge, NY 11788  
USA  
3701-04 Metroplaza Tower 1  
Hing Fong Road, Kwai Fong  
Hong Kong  
United Kingdom  
Telefon: (49) 89 45 49 49 0  
Fax: (49) 89 45 49 49 49  
Telephone: (1) 631 360 2222  
Fax: (1) 631 360 8222  
Telephone: (852) 26100 611  
Fax: (852) 24250 494  
Telephone (44) 161 622 4444  
Fax: (44) 161 622 4446  
© 2006 Published by Zetex Semiconductors plc.  
ZXLD1362EV3 User Guide issue 1  
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11-01-2008  
 

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