Supertex inc. HV9918DB1 High Current LED Driver Demoboard General Description Specifications The HV9918DB1 demoboard is a high current LED driver designed Parameter Value to drive one or two LEDs at 700mA from a 9.0 - 16VDC input. The demoboard uses Supertexs HV9918 hysteretic buck LED driver Input voltage 9.0 - 16VDC IC. Output voltage 2.0 - 7.0V The HV9918DB1 includes digital control of PWM dimming, which Output current 700mA 5% allows the user to dim the LEDs using an external, TTL-compatible Line and load regulation < 2% square wave source applied between DIM and GND. In this case, Output current ripple 5% (peak to peak) the PWM dimming frequency and duty ratio are set by the external square wave source. Full load efficiency 87% ( 12.0V input) The demoboard is protected against short circuit and open LED Open LED protection Yes conditions. It also includes thermal derating of the LED current us- ing an external NTC resistor to prevent over-heating. Output short circuit protection Yes Dimensions 25.4mm X 29.2mm The bottom of the HV9918DB1 is an exposed copper plane (con- nected to the input ground) which can be connected to a 1 square heatsink (eg: 374324B00035G from Aavid Thermalloy) to allow for operation in higher ambient temperatures without tripping the HV9918s built-in over temperature protection. Silk Screen Connection Diagram + - NTC Supertex Connections Input Connection: Connect the input DC voltage between 2. If dimming using an external PWM dimming source, VIN and GND terminals. connect the PWM source between the PWMD and GND terminals. Output Connection: Connect the LED(s) between LED+ (anode of LED string) and LED- (cathode of LED string) ter- NTC Thermistor Connection: minals. 1. If no thermal derating is required, the NTC terminal can be left open. PWM Dimming Connection: 1. If no PWM dimming is required, short PWMD and 2. If thermal derating of the LED current is required, the VDD terminals. NTC thermistor can be connected between NTC and GND terminals as shown. Doc. DSDB-HV9918DB1 Supertex inc. A032913 www.supertex.comHV9918DB1 Thermal derating in the HV9918DB1 uses the analog control Operation of the Board of PWM dimming function to limit the LED current when the The HV9918DB1 uses Supertexs HV9918 hysteretic buck LED temperature rises. During normal operating mode (con- LED driver IC to control the LED current. Since the regula- stant LED current no PWM dimming), the LED current will tion method controls both the peak and the valley current be PWM dimmed at 1.0kHz. During PWM dimming mode, in the inductor, the demoboard has excellent line and load the thermal derating function limits the maximum PWM dim- regulation. ming duty cycle so that the LED current does not exceed the maximum allowable current determined by the thermal The LED current can be controlled in by PWM dimming. derating circuit. PWM dimming can be achieved in one of two ways: 1. Analog control of PWM dimming where a 0-2V source Direct Control of PWM Dimming can be applied between NTC and GND terminals (the In the direct control method, the PWM dimming of the LEDs NTC terminal can also be used for thermal derating of is achieved by driving the PWMD terminal using an external the LED current as explained in the next section). square wave source. In this case, PWM dimming frequency and duty cycle are set by the external source. 2. Direct control of PWM dimming by applying a TTL com- patible square wave source between PWMD and GND In this mode, if the thermal derating function is not desired, terminals. NTC terminal should be left open. In this case, the recom- mended PWM dimming frequency can be anything up to Analog Control of PWM Dimming / Thermal De- 10kHz. rating Analog Control of PWM dimming can be accomplished by If thermal derating is desired, then the NTC thermistor should applying a 0 2.0V DC voltage between NTC and GND (the be connected between the NTC and GND terminals. In this DC voltage must have a 500A source/sink capability). In case, the PWM dimming frequency should be greater than this case, PWMD is connected to VDD and the LEDs are 1.2kHz. dimmed at 1.0kHz (as set by the capacitor at the RAMP pin of the IC). The duty cycle of the LED current can be adjusted by varying the external voltage at NTC (0V = 0% LED cur- rent and 2.0V = 100% LED current). The same NTC terminal can instead be used to de-rate the LED current based on the LED temperature, if desired. This would reduce the LED current as the LED temperature rises and prevents over-heating of the LED. An NTC resistor can be used to sense the temperature of the LED and this resis- tor can be connected between the NTC and GND terminals of the HV9918DB1. The demoboard is designed to operate with a 100k NTC thermistor which has a B-constant of 4250 (eg: NCP18WF104 from Murata). With this NTC thermistor, the LED current will start dropping at 85C and will reach about 350mA at 125C. Doc. DSDB-HV9918DB1 Supertex inc. A032913 2 www.supertex.com