ZXLD1356EV1 USER GUIDE DESCRIPTION The ZXLD1356EV1, Figure 1, is a PCB constructed using an FR4 base for evaluating the ZXLD1356 LED driver with internal switch in SOT23-5 package. 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. [1] 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 550mA with a 0.36Ω sense resistor, R1//R3. The 150uH inductor used in the circuit is based on a 30V nominal supply, which should be connected across +VIN and GND pins. Test point ADJ provides a connection point for DC or PWM dimming and shutdown. Note: The evaluation board does not have reverse polarity protection Warning: with 550mA output, the connected LED will be hot and very bright Figure 1: ZXLD1356EV1 evaluation board ZXLD1356 DEVICE DESCRIPTION The ZXLD1356 is a continuous mode inductive driver both in a TSOT23-5 package and DFN633 package, for driving one or more series connected 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 550mA. ZXLD1356 DEVICE FEATURES • Typical accuracy better than 0.8% • Enhanced thermal capability in DFN633 package • Drives one or more series-connected LEDs • LEDs up to 550mA. • Internal 60V switch. • Wide input voltage: 7V to 60V. • Inherent open circuit LED protection. • Brightness control using DC or PWM. • Internal PWM filter. Issue 1 – December 2008 © Diodes Incorporated, 2008 DEVICE APPLICATIONS • LED flashlights. • High Power LED driving. • Low-voltage halogen replacement LEDs. • Automotive lighting. • Illuminated signs. www.zetex.com www.diodes.com ZXLD1356EV1 ZXLD1356 Device Packages, Pin and Definitions TSOT23-5 and DFN633 package options ZXLD1356 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 a DC voltage (0.3V to 1.25V) or with a PWM signal to adjust output current • Connect a capacitor from this pin to ground to set the soft-start time. Connect a sense resistor, Rs= R1//R3, from the ADJ pin to VIN to sense the nominal output current. Nominal Iout = 0.2/ Rs Input voltage: 6V to 60V. Decouple to ground with a 100nF and a 10uF or higher ceramic capacitor depending on the input voltage[1]. ORDERING INFORMATION EVALBOARD ORDER NUMBER ZXLD1356EV1 DEVICE ORDER NUMBER ZXLD1356DAC ZXLD1356E5TA Please note: Evaluation boards are subject to availability and qualified leads. ZXLD1356EV1 EVALUATION BOARD REFERENCE DESIGN The ZXLD1356EV1 is an evaluation board configured to be used with the ZXLD1356 in SOT23-5 package, as 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 550mA with a 0.36Ω sense resistor R1. The device operates in continuous mode at approximately 120 kHz, with a 150uH inductor, when the system drives a single LED. 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 Issue 1 – December 2008 www.zetex.com www.diodes.com © Diodes Incorporated 2008 2 ZXLD1356EV1 filter and the voltage across the capacitor represents a more stable dc reading of current. Using this method, 200mV represents 0.55 Amp when using a 0.36Ω sense resistor. The ADJ pin connects to a low pass filter within the ZXLD1356 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 0.1ms/nF. For other reference designs or further applications information, please refer to the ZXLD1356 datasheet. Schematic Diagram Figure 2 shows the schematic for the ZXLD1356EV1 evaluation board. LED A R1//R3 Vin 5 4 C4 Vin V sense D1 C3 C1 L1 ADJ R2 3 ADJ ZXLD1356 1 LX LED K C2 GND GND Figure 2: Schematic for the evaluation board ZXLD1356EV1 Issue 1 – December 2008 www.zetex.com www.diodes.com © Diodes Incorporated 2008 3 ZXLD1356EV1 ZXLD1356 Operation In normal operation, when voltage is applied at +VIN, the ZXLD1356 internal NDMOS switch is turned on. Current starts to flow through sense resistor R1//R3, 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//R3. The internal circuit of the ZXLD1356 senses the voltage across R1//R3 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//R3, 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//R3, which is sensed by the ZXLD1356. A voltage proportional to the sense voltage across R1//R3 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 resistors R1 and R3) to the LEDs. Please refer to the datasheet for the threshold limits, ZXLD1356 internal circuits, electrical characteristics and parameters. ZXLD1356EV1 Evaluation Board - BOM Ref R1 R2 R3 C1 C2,C4 C3 L1 D1 U1 Value 0.36R 1kΩ Package 1206 0805 10uF 100V 100nF, 100V 100nF 150uH 100V, 2A ZXLD1356 SMD 0805 1206 SMB TSOT23-5 Part Number SR732BTTDR360F Generic Not fitted NACEW100M1006.3x8TR13F NMC0805X7R104K100TRPLPF NMC1206X7R104K100TRPLP3KF NPIS104F151MTRF B2100 ZXLD1356E5TA Manufacturer KOA - Notes 1%, 100ppm - NIC NIC NIC NIC DIODES inc Zetex Electrolytic - 20% 20% 150uH Schottky diode DC-DC converter The FR4 PCB design guarantees a good thermal dissipation for the ZXLD1356 device. 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 500mA output, the board temperature rises by around 50C from ambient after 30 minutes of operation. Figure 3: Component layout and circuit board view Issue 1 – December 2008 www.zetex.com www.diodes.com © Diodes Incorporated 2008 4 ZXLD1356EV1 ZXLD1356EV1 Connection Point Definition Name Description +VIN Positive supply voltage. GND 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 connects to the external LED anode LED K connects to the external LED cathode LED A LED K ZXLD1356EV1 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 500mA 5. LX waveforms can be acquired using the test point J1 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 and R3 2. Calculate and fit a new sense resistor, R1//R3, the value of which is based on the required LED current without dimming. R1//R3 can be calculated using following equation : R1//R3 = 0.2(V / IOUT) where IOUT = the LED current. R1,R3 = the sense resistors value in ohms. 0.2V is the nominal sense voltage with ADJ open circuit or set to 1.25V. Issue 1 – December 2008 www.zetex.com www.diodes.com © Diodes Incorporated 2008 5 ZXLD1356EV1 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] ZXLD1356 Datasheet – www.zetex.com Issue 1 – December 2008 www.zetex.com www.diodes.com © Diodes Incorporated 2008 6 ZXLD1356EV1 INTENTIONALLY BLANK Issue 1 – December 2008 www.zetex.com www.diodes.com © Diodes Incorporated 2008 7 ZXLD1356EV1 Definitions Product change Diodes Incorporated 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 Diodes Inc. 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. Diodes Inc. 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 Diodes 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 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 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 Diodes Inc. 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 Diodes sales office. Quality of product Diodes Zetex Semiconductors Limited 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 or www.diodes.com. Diodes 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 Diodes 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 Diodes 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” “Last time buy (LTB)” “Not recommended for new designs” “Obsolete” Datasheet status key: “Draft version” “Provisional version” “Issue” 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. 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