QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 994 THREE CHANNEL LED BALLASTER WITH PWM LT3003 DESCRIPTION

Transcription

1 LT00 DESCRIPTION Demonstration circuit features the LT00 three channel LED ballaster with in a 0-lead MSOP thermally enhanced MSE package. The demonstration circuit is designed to ballast three channels of LED current from 00mA to 0mA per channel. The dimming function of the LT00 eliminates the need for discrete MOSFETs. The LT00 internally performs the level-shift required for non-ground referred dimming in the buck mode and buckboost mode topologies allowing dimming input requirements to remain at logic-level. dimming capabilities reach 000: at 00Hz. Over temperature protection provides two open-collector pull-down outputs for direct interface with the compensation pin of most LT LED drivers and for use with a microcontroller. Additional thermal shutdown prevents the LT00 from getting too hot. The LT00 can be configured in all LED driver topologies as long as there are three strings of LEDs and the pin voltage requirements are met. The boost, buck mode, buck-boost mode, SEPIC, and buck LED driver topologies can all use the LT00 three channel ballaster with. The shutdown pin can be tied to the switcher shutdown pin or in buck-boost mode it must be tied to the pin. When a single LED channel is open and has no current, the other two channels cut back their current to zero or almost zero in order to protect themselves. The LED current per string rating is between 00mA and 0mA. The maximum voltage on pin is V and the maximum voltage on pin is 0V. For more details, please read the datasheet. Design files for this circuit board are available. Call the LTC factory. LT is a registered trademark of Linear Technology Corporation QUICK START PROCEDURE Follow the test procedure outlined below and see Figure to setup and test the LT00 in the boost LED driver topology. The LT00 needs to run with three strings of LEDs and an LED driver. The LEDs and LED driver do not come with DCA, it is a standalone demonstration circuit that is meant to be used with different LED drivers in different topologies for evaluation.. Connect the three strings of LEDs from the LED+ terminal of the boost LED driver to the three LED terminals of the DCA.. Connect the terminal of the DCA to the LED- () terminal of the boost LED driver.. Connect the shutdown terminal of the DCA to the shutdown terminal of the LED driver or to the terminal of the DCA if the shutdown function is not being used.. Connect the terminal of the DCA to the output voltage at the output capacitor of the boost LED driver. The DCA shown in Figure does not have a terminal for this node, so a wire has to be soldered to the output capacitor.. Connect a.v or V bench supply with power OFF to the and terminals of DCA.. Connect a V to 0V bench supply with power OFF to the and terminals of DCA.. Turn on the input power supply for the DCA.

2 . Turn on the input power supply for the boost LED driver and set the voltage.. Observe the LEDs working properly at 00mA to 0mA per string without looking straight at the LEDs. The extreme brightness may be harmful to the eye. 0. For dimming, tie the terminal of the DCA to the dimming input of the boost LED driver if the driver has a dim input. Attach a logic-level dimming pulse waveform to the terminal of the DCA at 00Hz with as high as 000: dimming ratio determined by the boost LED driver. Observe the dimming brightness of the LEDs without looking straight at them. DCA OPTIONS Figure Proper Measurement Equipment Setup with DCA in Boost Mode JP=JP=open PIN VOLTAGE RANGE The operating pin voltage range for pin on the LT00 is V to 0V. In most cases, it is not desirable to tie to the highest rail available due to both excessive IC power consumption and to LED string current matching accuracy. It is most optimal to tie the pin to a voltage that is between V and V higher than the pin voltage. In the cases of boost LED driver and buck LED driver (LT / LT), when the pin is tied to ground, a.v or V supply on the pin of the LT00 is optimal for best LED string current matching. In buck-boost mode and buck mode LED topologies, the pin of the LT00 should be tied to the pin rail (Vout and Vin of the LED driver respectively) through a zener diode that has a breakdown voltage of Vf = VfLED V approximately. This makes the pin voltage about V above the pin voltage that is not ground-referred. DIMMING DCA is designed to provide LED dimming in every LED driver topology with a logic-level dimming input directly tied into the pin of the LT00. The necessary level-shifting of the dimming signal is designed into the IC, eliminating extra level-shifting discrete components from the circuit in certain topologies and replacing the dimming MOSFET in all topologies. Some LED drivers have a pin that can be tied to the pin of the LT00 and to the same signal as shown in Figures,, and. The LT00 function also works with LED drivers that do not have a pin. Please refer to the datasheet for details. When not in use, the pin of the LT00 can be left floating. There is an internal pull-up on the dimming pin that eliminates the need to tie this pin high. In

3 buck-boost mode, the LT00 pin is shown to be tied to the shutdown pin of the LT00. This is needed when dimming is being used so that the pin current does not drain the output capacitor during off time by putting the IC in shutdown. If this is not an issue, the shutdown pin can be released from the pin and should be tied high or to the system shutdown signal instead. When the two pins and / are not tied together and dimming is being used, the maximum dimming ratio is reduced when compared with the case where the two pins are tied together. BOOST, BUCK, BUCK MODE, AND BUCK-BOOST MODE TOPOLOGIES The LT00 can be configured to work with any LED driver topology. The different topologies such as boost, buck, buck mode, and buck-boost mode are shown in the LT00 datasheet and below. The different topologies accommodate the different relationships between the input voltage range and the LED string voltage range. The LT00 datasheet covers the different topologies as shown in the figure below. Although these topology schematics are shown in the LT00 datasheet, the pin should not generally be tied directly to or VOUT of the LED driver circuit. A zener diode or other supply should be used with the pin to keep the pin voltage between V and V for minimal IC heating and for optimal LED string current matching. Figure Boost LED driver topology Figure Buck mode LED driver topology

4 Figure Buck-boost mode LED driver topology

5 Figure DCA schematic with features Tie // to three LED strings Tie to boost LED driver VOUT V-V U LT00EMSE 0 Tie to boost LED driver ground Tie / to LED driver / Tie / to LED driver gm output (Vc) logic level input may also be tied to LED driver.v or V Tie to.v or V source C uf.v R M If / of LT00 is pulled-up externally, R m ay not be needed. Figure DCA boost LED driver setup - / & / terminals, / terminal, terminal float is okay (JP, JP = OPEN)

6 Tie to buck mode LED driver P V-V D Vz = VfLED - V Tie // to three LED strings U LT00EMSE 0 COUT Tie to LED driver inductor and COUT LED driver P L LED driver VSW Tie / to LED driver / Tie / to LED driver gm output (Vc) logic level input C uf 0V R M If / of LT00 is pulled-up externally, R m ay not be needed. Figure DCA buck mode LED driver setup terminal, / & / terminals, terminal, / terminal float is okay (JP, JP = OPEN)

7 Tie // to three LED strings U Tie to buck-boost mode LED driver VOUT V-V D Vz = VfLED - V LT00EMSE Tie to LED driver P 0 Tie / to LED driver gm output (Vc) Tie / to with JP when dimming logic level input C uf 0V Figure DCA LT00 buck-boost mode LED driver setup terminal, / & / terminals float is okay pin float is okay, but when not dimming / must be connected to system shutdown signal or (JP = OPEN, JP = OPEN when not dimming)

8 V-V Tie to buck LED driver P Tie // to three LED strings U LT00EMSE 0 Tie to buck LED driver ground Tie / to LED driver / Tie / to LED driver gm output (Vc) logic level input may also be tied to LED driver.v or V Tie to.v or V source C uf.v R M If / of LT00 is pulled-up externally, R m ay not be needed. Figure DCA LT00 buck LED driver setup with ICs such as the LT/LT terminal, / terminal, / & / terminals float is okay (JP, JP = OPEN)

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