QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 994 THREE CHANNEL LED BALLASTER WITH PWM LT3003 DESCRIPTION Demonstration circuit 994 features the LT3003 three and the pin voltage requirements are met. The boost, channel LED ballaster with PWM in a 10-lead MSOP buck mode, buck-boost mode, SEPIC, and buck LED thermally enhanced MSE package. The demonstration driver topologies can all use the LT3003 three circuit is designed to ballast three channels of LED channel ballaster with PWM. The shutdown pin can current from 100mA to 350mA per channel. The be tied to the switcher shutdown pin or in buck-boost PWM dimming function of the LT3003 eliminates the mode it must be tied to the PWM pin. need for discrete MOSFETs. The LT3003 internally When a single LED channel is open and has no performs the level-shift required for non-ground current, the other two channels cut back their current referred PWM dimming in the buck mode and buck- to zero or almost zero in order to protect themselves. boost mode topologies allowing PWM dimming input The LED current per string rating is between 100mA requirements to remain at logic-level. PWM dimming and 350mA. The maximum voltage on VMAX pin is capabilities reach 3000:1 at 100Hz. Over temperature 48V and the maximum voltage on VIN pin is 40V. protection provides two open-collector pull-down For more details, please read the datasheet. outputs for direct interface with the compensation pin of most LT LED drivers and for use with a Design files for this circuit board are available. Call microcontroller. Additional thermal shutdown the LTC factory. prevents the LT3003 from getting too hot. LT is a registered trademark of Linear Technology Corporation The LT3003 can be configured in all LED driver topologies as long as there are three strings of LEDs QUICK START PROCEDURE Follow the test procedure outlined below and see driver or to the VIN terminal of the DC994A if Figure1 to setup and test the LT3003 in the boost LED the shutdown function is not being used. driver topology. The LT3003 needs to run with three 4. Connect the VMAX terminal of the DC994A to strings of LEDs and an LED driver. The LEDs and LED the output voltage at the output capacitor of driver do not come with DC994A, it is a standalone the boost LED driver. The DC841A shown in demonstration circuit that is meant to be used with Figure 1 does not have a terminal for this different LED drivers in different topologies for node, so a wire has to be soldered to the evaluation. output capacitor. 1. Connect the three strings of LEDs from the 5. Connect a 3.3V or 5V bench supply with LED+ terminal of the boost LED driver to the power OFF to the VIN and GND terminals of three LED terminals of the DC994A. DC994A. 2. Connect the VEE terminal of the DC994A to 6. Connect a 3V to 10V bench supply with power the LED- (GND) terminal of the boost LED OFF to the VIN and GND terminals of DC841A. driver. 7. Turn on the input power supply for the 3. Connect the shutdown terminal of the DC994A. DC994A to the shutdown terminal of the LED 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 994 THREE CHANNEL LED BALLASTER WITH PWM 8. Turn on the input power supply for the boost LED driver and set the voltage. 9. Observe the LEDs working properly at 100mA to 350mA per string without looking straight at the LEDs. The extreme brightness may be harmful to the eye. 10. For PWM dimming, tie the PWM terminal of the DC994A to the PWM dimming input of the boost LED driver if the driver has a PWM dim input. Attach a logic-level PWM dimming pulse waveform to the PWM terminal of the DC994A at 100Hz with as high as 3000:1 PWM dimming ratio determined by the boost LED driver. Observe the PWM dimming brightness of the LEDs without looking straight at them. Figure 1 Proper Measurement Equipment Setup with DC841A in Boost Mode JP1=JP2=open DC994A OPTIONS VIN PIN VOLTAGE RANGE PWM DIMMING The operating pin voltage range for VIN pin on the DC994A is designed to provide LED PWM dimming in LT3003 is 3V to 40V. In most cases, it is not desirable to every LED driver topology with a logic-level PWM dim- tie VIN to the highest rail available due to both excessive ming input directly tied into the PWM pin of the LT3003. IC power consumption and to LED string current match- The necessary level-shifting of the PWM dimming signal ing accuracy. It is most optimal to tie the VIN pin to a is designed into the IC, eliminating extra level-shifting voltage that is between 3V and 7V higher than the VEE discrete components from the circuit in certain topolo- pin voltage. In the cases of boost LED driver and buck gies and replacing the PWM dimming MOSFET in all to- LED driver (LT3474 / LT3475), when the VEE pin is tied pologies. to ground, a 3.3V or 5V supply on the VIN pin of the Some LED drivers have a PWM pin that can be tied to LT3003 is optimal for best LED string current matching. the PWM pin of the LT3003 and to the same PWM signal In buck-boost mode and buck mode LED topologies, the as shown in Figures 2, 3, and 4. The LT3003 PWM func- VIN pin of the LT3003 should be tied to the VMAX pin tion also works with LED drivers that do not have a rail (Vout and Vin of the LED driver respectively) through PWM pin. Please refer to the datasheet for details. a zener diode that has a breakdown voltage of Vf = When not in use, the PWM pin of the LT3003 can be left VfLED 5V approximately. This makes the VIN pin volt- floating. There is an internal pull-up on the PWM dim- age about 4V above the VEE pin voltage that is not ming pin that eliminates the need to tie this pin high. In ground-referred. 2