QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 773 SYNCHRONOUS 1MHZ LUXEON III WHITE LED DRIVER LTC3441 & LTC2050 DESCRIPTION Demonstration circuit 773 is a synchronous buck-boost optional MODE/SYNC terminal can be used to synchro- 1MHz Luxeon III white LED driver featuring the LTC3441 nize the LTC3441 clock with an external clock. and LTC2050. The board is optimized for 3.9V LED for- The LTC2050 is used to control a constant LED current ward voltage output at 1000mA load current and a single at the output with the minimum amount of power dissi- lithium-ion input voltage range of 3V to 4.2V. With its pation in the sense resistor. The five-pin LTC2050IS5 is high frequency, synchronous buck-boost internal power used for minimum components and minimum pins, but switches, low quiescent current, 1MHz switching fre- the LTC2050IS6 with a shutdown pin can be used for quency and thermally enhanced package, the LTC3441 is extremely low quiescent current. 1 a very versatile and powerful IC for driving Luxeon III The LTC3441 and LTC2050 datasheets give complete LEDs that require both step-up and step-down capability descriptions of the parts including operation and appli- from lithium-ion supplies used in very compact hand- cations information. The datasheets must be read in held solutions. conjunction with this Quick Start Guide for demonstra- The LTC3441 1MHz switching frequency allows all of the tion circuit 773. The LTC3441 is assembled in a small components to be small, surface mount devices. The 10-pin thermally enhanced package with exposed pad. current-mode control topology creates fast transient Lumileds LXHL-PW09 Luxeon III LED emitter has an response and good loop stability with a minimum num- exposed pad slug for thermal enhancement. Proper ber of external components. The LED pushbutton is board layout is essential for maximum thermal perform- used to manually turn on the LED. The SHDN terminal ance. The LXHL-PW09 datasheet is found on Lumileds can be used to program pulses of light from an external website www.lumileds.com. source for certain flash applications. The DIM terminal Design files for this circuit board are available. Call can be used to program the LED for dimmer operation the LTC factory. than 1A LED current using a external PWM signal. The . Table 1. Typical Performance Summary (T = 25C) A PARAMETER CONDITION VALUE Input Voltage Range 34.2V V = 3.6V, U2 LTC2050IS6 w/ Shutdown 1 1.4A IN LED OFF Input Current 1 V = 3.6V, U2 LTC2050IS5 w/out Shutdown 1 1.08mA IN V V = 3V to 4.2V, LED ON, I = 1000mA 3.9V LED IN LED I V = 3V to 4.2V, LED ON 1000mA LED IN LED Ripple Current V = 3.6V, LED ON, I = 1000mA 25mA IN OUT PKPK Switching Frequency V = 3V to 4.2V, LED ON 1MHz IN Efficiency V = 3.6V, I = 1000mA, LED ON 84% IN LED LED Brightness V = 3.6V, I = 1000mA, LED ON 80LM IN LED NOTE: 1 Replace LTC2050IS5 with LTC2050IS6 for low quiescent current during LED OFF. Tie SHDN pin of LTC2050IS6 to SHDN pin of LTC3441. DC773A is stuffed with LTC2050IS5 without a shutdown pin. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 773 SYNCHRONOUS 1MHZ LUXEON III WHITE LED DRIVER QUICK START PROCEDURE Demonstration circuit 773 is easy to set up to evaluate the performance of the LTC3441 & LTC2050. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: NOTE: Make sure that the input voltage does not exceed 4.2V. NOTE: The shutdown function, dim function, and sync function are optional and their terminals can be left float- ing (disconnected) if not being used. 1. Connect the power supply (with power off), load, and meters as shown in Figure 1. 2. After all connections are made, turn on input power and verify that the LED turns on when the LED ON button is depressed. NOTE: If the LED is not bright or not on, make sure that the current limit on the supply is not set too low. 3. Once the operation of the LED is established, adjust Figure 1. Proper Measurement Equipment Setup the supply within the operating range and observe the LED brightness, LED ripple, efficiency and other parameters. OPTIONAL FUNCTIONS SHUTDOWN / SOFT-START The LED ON pushbutton is used to manually demon- strate how bright the LXHL-PW09 LED is with 1000mA of LED current. However, for some flash applications, a timed pulse is required. The SHDN terminal is used to attach an external pulsed source to drive the LED at 1000mA without pressing the LED ON pushbutton. Please see the LTC3441 datasheet for the soft-start func- tion and its implementation using the SHDN/SS terminal. DIM Demonstration Circuit 773 has a DIM terminal for dim- ming the LED. Typically the LED provides 80LM with 1A constant current. However, for less current, the DIM function may be used by switching in a lower resistance in the feedback path. Figure 2 demonstrates where to add the parallel dimming resistor. For 50% dimming, 2