ZXLD1374EV1 BUCK LED DRIVER USER GUIDE 0-1.5A DC DVM GND 8-48V 2A DC PSU 1 - 15 LEDs 1.5A 4.5V 0 – 4.5V Status steps 0V Open Drain output 2.5V = 200% 125mV = 10% -t° Thermal connection Fig. 1 ZXLD1374EV1 Evaluation board connection diagram Issue 1 – September 2010 © Diodes Incorporated, 2010 www.diodes.com ZXLD1374EV1 Fig. 2 ZXLD1374EV1 Schematic Diagram Issue 1 – September 2010 www.diodes.com © Diodes Incorporated 2010 2 ZXLD1374EV1 PARTS LIST Ref U1 D1 Value 1.5A LED Driver Freewheeling diode 3A 100V NOT FITTED 33uH 2.3A Package TSSOP20L- EP DFN3030 Part Number ZXLD1374 SBR3U100LP Manufacturer Diodes Diodes Contact Details www.diodes.com www.diodes.com SOT23 DDZX15 MS1246-333MLB NPIS24H330MTRF 744-7715330 Diodes Coilcraft NIC Comps. Wurth www.diodes.com www.coilcraft.com www.niccomp.com www.weonline.com C1 C2 C5 C8 C3 C4 100pF 10V 1uF 100V X7R 0805 1206 2.2uF 100V X7R 1812 GRM31CR72A105 KA01L GRM43ER72A225 KA01L generic Murata / generic Murata / generic C6 C7 C9 R1 R2 R3 R5 R6 R8 R14 R4 R7 R11, R13 NOT FITTED 100nF 100V X7R 0R3 0R 0805 1206 0805 generic generic generic 1K3 47K NOT FITTED 0805 0805 1206 generic generic D2 L1 www.murata.com www.murata.com NOTES The PCB is supplied with R3 and R8 0R0 resistors fitted. The ‘ADJ’ pin and the ‘TADJ’ pin are disabled. ‘VIN’ and ‘VAUX’ are shorted on ZXLD1374EV1 The LED current of the ZXLD1374EV1 boards = 1.5A with 2x // 0R3 = 0R15 (R1 & R2) The ZXLD1374 ‘VAUX’ pin can be driven from a separate supply instead of the ‘VIN’ voltage. To do this, remove R14, fit R11 = 10k0, fit R13 = 10k0. Use Zener diode D2 to keep ‘VAUX’ pin <15V. For other reference designs or more applications information, please see the ZXLD1374 datasheet. OPERATION In Buck mode the LED current is sensed by the series resistor (R1 // R2). An output from the control loop responsible for sensing this current drives the input of an internal comparator. The comparator then 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, the LED and D1, to ‘VIN’ . When the inductor current has gone low, ‘LX’ goes low, the cycle of events repeats and so 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 equal to the average 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. Issue 1 – September 2010 www.diodes.com © Diodes Incorporated 2010 3 ZXLD1374EV1 Fig. 3 Waveforms Issue 1 – September 2010 www.diodes.com © Diodes Incorporated 2010 4 ZXLD1374EV1 ADJ Terminal (DC output current adjustment) On the ZXLD1374EV1, R3 connects the ‘ADJ’ pin to ‘VREF’ to give 100% LED current. The ‘ADJ’ pin can 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 ‘ADJIN’ and ‘GND’. The voltage ‘VADJ ‘ can be derived from a resistor-divider connected between ‘REF’ and ‘GND’. ‘ADJ’ has a high impedance within its normal operating voltage range. An internal 2.6V clamp protects the device against high input voltages and limits the maximum output current to about 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 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 shutdown, most of the circuitry inside the device is turned 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% current 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 ZXLD1374EV1, Rth is 1K3 (R4). 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 1 – September 2010 www.diodes.com © Diodes Incorporated 2010 5 ZXLD1374EV1 BOARD LAYOUT Issue 1 – September 2010 www.diodes.com © Diodes Incorporated 2010 6 ZXLD1374EV1 INTENTIONALLY BLANK Issue 1 – September 2010 www.diodes.com © Diodes Incorporated 2010 7 ZXLD1374EV1 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. 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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. 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