DEMO CIRCUIT 1285 LT3598 QUICK START GUIDE LT3598 6-String 30mA LED Driver with 1.5% Current Matching DESCRIPTION WARNING! Do not look directly at operating LED. This circuit produces light that can damage eyes. Demonstration circuit 1285 is a 6-String 30mA LED Driver with 1.5% Current Matching featuring the LT3598. The LT3598 is a step-up DC/DC converter designed to drive up to 6-strings of LEDs at an output voltage up to 44V. The LED strings are connected to internal current sources where the current level is set with an external resist. The demonstration circuit drives 20mA through each LED string. Each string can have up to 10 white LEDs. The circuit operation frequency is set to 1MHz. Parameters such as the LED current; the switching frequency, etc can be modified easily based on the demo circuit. When a string is not used, tie its LED pin to VOUT. Any unused string is no longer in the regulation loop. Direct paralleling multiple strings together to achieve higher per string current is allowed. To paralleling strings, tie the respective LEDn pins together. OPENLED indicator flags should any string be left open. To improve efficiency, it is recommended that VIN is between 3.2V and 5.5V. The VIN bias capacitor of the demo circuit is rated at 6.3V. PWM dimming ratio can be as high as 3000:1. The LT3598 datasheet gives complete descriptions of the part, operation and application information. The datasheet must be read in conjunction with this quick start guide for working on or modifying the demo circuit 1285. Design files for this circuit board are available. Call the LTC factory. L, LTC, LTM, LT are trademarks of Linear Technology Corporation. Other product names may be trademarks of the companies that manufacture the products. PERFORMANCE SUMMARY Specifications are at TA = 25°C SYMBOL VIN PVIN IQ FSW ILED IM Eff DPWM PARAMETER Input Supply Range Power Input Supply Range** Quiescent Current Switching Frequency LED String Current LED String Current Matching*** Efficiency PWM dimming ratio CONDITIONS MIN 3.2 3 PWM=0V, Not switching 0.9 19.5 VIN = 3.3V; PVIN = 12V; ILED = 20mA PVIN = 12V TYP 3.5 1 20 0.5 90 3000:1 MAX 5.5* 40 5 1.1 20.7 1.5 UNITS V V mA MHz mA % % *: Limited by the voltage rating of the bias capacitor, C2, on the demo circuit. The IC rating is 30V. **: MIN PVIN depends on LED string voltages and the Maximum Switch Duty Cycle (specified on page 3 of the datasheet). PVIN greater than MAX LED string voltage is permitted but power dissipation needs to be taken into considerations. ***: Specifications apply over the full operating temperature range. 1 LT3598 QUICK START PROCEDURE Demonstration circuit 1285 is easy to set up to evaluate the performance of the LT3598. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 1. With power off, connect the input power supply to VIN and GND. 2. Connect the power input power supply to PVIN and GND. 3. Tie PWM to VIN or a PWM signal. 2 4. Connect LED strings to LEDn+ and LEDn-. If any string is not used, tie LEDn- to LEDn+, where n is the string number (between 1 and 6). 5. Turn on power supplies for VIN and PVIN. NOTE. Make sure that VIN does not exceed 5.5V and PVIN does not exceed 40V. 6. Check for the proper LED voltage and current. LT3598 Figure 1. Proper Measurement Equipment Setup 3 LT3598 L1 E6 C1 2.2uF 50V E5 C7 10uF 50CE10BJ OPT VISHAY IHLP-2525BD-01 E9 E11 E13 E15 E17 E19 LED1+ LED2+ LED3+ LED4+ LED5+ LED6+ VIN U1 7 VIN 20 2 15 14 R7 100K 1% 16 18 23 LED1 RT LED2 LED3 VREF LED4 R6 10K 1% LED5 R2 2.4M 1% 178K 1% C10 47pF 1 2 3 4 5 6 CTRL 12 R9 13 R8 14.7K 1% VC 9 LED6 11 10 E20 R12 107K 1% 4 NC SY NC SS CTRL 100K 1% PWM C8 0.1uF R5 51.1K 1% R11 FB 17 E7 SHDN TSET E4 24 OPENLED GND 100K 1% SY NC VO_SW R4 76.8K 1% 1 JP1 PWM LED1LED2LED3LED4LED5LED6E8 E10 E12 E14 E16 E18 ON 3 R3 VIN 25 OFF LT3598EUF VOUT 22 E3 ISET E2 R1 100K 1% SW C2 1uF 6.3V 21 OPENLED VOUT 1 40V 1A E1 3.2V - 5.5V GND + 19 VIN D1 2 3V - 40V GND 10uH 8 PVIN R10 C4 C9 0.1uF 100pF 3K 1% C5 10nF C6 4.7uF 50V C3 4.7uF 50V