ZXLD1374EV2 BUCK/BOOST LED DRIVER USER GUIDE BUCK/BOOST 0-500mA DC GND 8-48V 2A DC PSU 1 - 15 LEDs 350mA 4.5V 0 – 4.5V Status steps 0V Open Drain output 2.5V = 200% 125mV = 10% -t° Thermal connection Fig.1 ZXLD1374EV2 Evaluation board connection diagram Issue 3 – May 2011 © Diodes Incorporated, 2010 www.diodes.com ZXLD1374EV2 Fig2. Schematic diagram Issue 3 – May 2011 www.diodes.com © Diodes Incorporated 2010 2 ZXLD1374EV2 PARTS LIST Ref U1 Q2 Q3 D1 D2 D3 Z1 L1 C1 C2 C5 C8 C3 C4 C9 C10 C6 C7 C11 C12 R1 R2 R4 R7 R9 R10 R3 R5 R6 R8 R14 R18 R13 R15 R11 R16 R17 R19 Value 1.5A LED Driver 60V General Purpose MOSFET NOT FITTED Freewheeling diode 3A 100V 1A 60V diode NOT FITTED 62V 250mW Zener Diode 33uH 2.1A Package TSSOP20L- EP Part Number ZXLD1374EST20TC Manufacturer Diodes Contact Details SOT23 2N7002 Diodes www.diodes.com PowerDI5 PDS3100 Diodes www.diodes.com PowerDI123 DFLS160 Diodes 100pF 50V COG 1uF 100V X7R 2.2uF 100V X7R NOT FITTED 100nF 100v X7R 0R3 1K3 47K 120K 1% 36K 1% 0R0 0805 0R0 2K NOT FITTED www.diodes.com www.diodes.com SOT23 1206 1812 BZX84C62 Diodes www.diodes.com MSS1038-333MLB NPIS104F330MTRF 744-066-330 Coilcraft NIC Comps. Wurth Generic www.coilcraft.com www.niccomp.com www.we-online.com GRM31CR72A105K A01L GRM43ER72A225K A01L Murata www.murata.com Murata www.murata.com 0805 1206 0805 0805 0805 0805 0805 Generic Generic Generic Generic Generic Generic 1206 0805 Generic Generic Issue 3 – May 2011 www.diodes.com © Diodes Incorporated 2010 3 ZXLD1374EV2 NOTES The PCB is supplied with R3 and R8 0R0 resistors fitted. The ‘ADJ’ pin and the ‘TADJ’ pins are disabled. Boost-only mode is selected by changing PL1 selector. In Boost mode, the total LED output voltage is <=60V. The supply voltage for the ZXLD1374EV2 is >=6V, <= (total LED voltage). In Buck-boost operation, the input voltage range is limited by the max LX voltage and the LED voltage. >=6V, <=(60V – VLED). For other reference designs or further applications information, please refer to the ZXLD1374 datasheet. Q2 and Z1 protect the circuit from open-circuit LEDs. The overvoltage threshold of the evaluation board is 62V. (Set by the 62V Zener diode Z1) Do not use a Zener diode of higher voltage than 62V since absolute max rating for the ZXLD1374 is 65V. For Boost and Buck-boost modes the average LED current is: ILED= average IINDUCTOR x R10/(R9+R10) The nominal current, ILED for the evaluation board is set to 350mA. OPERATION In Boost and Buck-boost mode the LED current is sensed by the series resistor (R1 // R2). An output from the control loop drives the input of a internal comparator. The comparator drives the gate of the internal NMOS switch transistor. When the NMOS switch is on (LX pin low), current flows from VIN, via (R1 // R2), inductor and switch to ground and increases until a high value is reached. Then, the switch turns off (LX pin high) and the current flows through (R1 // R2), the inductor, D1 and the LED, to ‘VIN’ (Buck-boost mode), or ‘GND’ (Boost mode). When the inductor current has gone low, ‘LX’ goes low, and the cycle of events repeats resulting in the circuit oscillates. The average current in the LEDs is equal to the average of the maximum and minimum threshold currents. The ripple current (hysteresis) is equal to the difference between the thresholds. The average current in the LED is always less than the average current in the inductor and the ratio between these currents is set by the values of resistors R9 and R10. The peak current in the LED is equal to the peak current in the inductor. The control loop keeps the average LED current at the level set by the voltage on the ‘ADJ’ pin. Loop compensation is achieved by C1. Bootstrap Circuit For input voltages between 6-12V and high switch currents that require a fully enhanced MOSFET, it is required to use the bootstrap network D2-R13 and remove R11. Issue 3 – May 2011 www.diodes.com © Diodes Incorporated 2010 4 ZXLD1374EV2 For input voltages higher than 12V and high switch currents, the MOSFET is fully enhanced. The bootstrap network D2-R13 is not required and can be removed. The resistor R11 (0R0) need to be fited to supply VAUX. Gate Voltage ~15 V 0V VVIN VVIN -225 mV ISM Voltage Coil current 225 mV/R s 0A Diode current 225 mV/R s Average Diode current 0A tOFF tON Fig. 3 Waveforms for Boost and Buck-boost modes Issue 3 – May 2011 www.diodes.com © Diodes Incorporated 2010 5 ZXLD1374EV2 ADJ Terminal (DC output current adjustment) On the ZXLD1374EV2, the ‘ADJ’ pin R3 connects the internal 1.25V reference (VREF) give 100% LED current. The ADJ pin can also be driven with an external DC voltage >=125mV and <= 2.5V to adjust the LED current to >= 10% and <=200% of the nominal value. To do this, remove R3, fit R5 and apply an external DC voltage between the connectors ‘ADJIN’ and ‘GND’ The voltage VADJ can be derived from a resistor-divider connected between ‘REF’ and ‘GND’. ‘ADJ’ has high impedance within its normal operating voltage range. An internal 2.6V clamp protects the device against excessive input voltage and limits the maximum output current to approximately 4% above the maximum current set by ‘VADJ‘ if the maximum input voltage is exceeded. PWM Terminal (PWM output current control/dimming) The LED current can be adjusted digitally, by applying a low frequency PWM logic signal to the ‘PWM’ pin to turn the controller on and off. This will produce an average output current proportional to the duty cycle of the control signal. During PWM operation, the device remains powered up and only the output switch is switched by the control signal. The device can be shut down by taking the PWM pin to < 0.4V for >15ms (with a short to 0V or suitable open collector NPN, or open drain NMOS transistor). In the shutdown state, most of the circuitry inside the device is off and the quiescent current will be typically 90µA. TADJ Terminal (Thermal control of LED current) The ‘Thermal control’ circuit monitors the voltage on the ‘TADJ’ pin and reduces the output current linearly if the voltage on ‘TADJ’ < 625mV. An NTC thermistor and resistor can be connected to set the voltage on the ‘TADJ’ pin = 625mV at the required threshold temperature. This will give 100% LED current below the threshold temperature and <100% above it as shown in the graph. The temperature threshold can be changed by adjusting the value of Rth and/or the thermistor to suit the LED used. On the ZXLD1374EV2, Rth is 1K3 (R4). In order to use thermal control, remove R8, fit R6, and fit a 10K NTC Negative Temperature Coefficient) type thermistor between ‘TADJ’ and ‘GND’. This will set the threshold temperature to ~ 90ºC. Thermal control by LED current reduction Fig. 4 Thermal control The Thermal Control feature can be disabled by connecting TADJ to REF through the jumper resistor R8. Issue 3 – May 2011 www.diodes.com © Diodes Incorporated 2010 6 ZXLD1374EV2 BOARD LAYOUT Issue 3 – May 2011 www.diodes.com © Diodes Incorporated 2010 7 ZXLD1374EV2 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. 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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 Kustermannpark Balanstraße 59, D-81541 München Germany 7F, No. 50, Min Chuan Road Hsin-Tien Taipei, Taiwan Rm. 606, No.1158 Changning Road Shanghai, China Tel: (+86) 215 241 4882 Room A1103-04, ANLIAN Plaza, #4018 Jintian Road Futian CBD, 6 Floor, Changhwa B/D, 1005-5 Yeongtong-dong, Yeongtong-gu, Suwon-si, Gyeonggi-do, Korea 443-813 Fax: (+1) 805 446 4850 Tel: (+49) 894 549 490 Fax: (+49) 894 549 4949 Tel: (+886) 289 146 000 Fax: (+886) 289 146 639 Fax (+86) 215 241 4891 Shenzhen, China Tel: (+86) 755 882 849 88 Fax: (+86) 755 882 849 99 Tel: (+82) 312 731 884 Fax: (+82) 312 731 885 Issue 3 – May 2011 www.diodes.com © Diodes Incorporated 2010 8