DEMO CIRCUIT 1327B LT3599 QUICK START GUIDE LT3599 4-Channel 120mA LED Driver with +/-1.5% Current Matching DESCRIPTION paralleling multiple strings together to achieve higher WARNING current per string is allowed. To paralleling strings, tie the respective LEDn pins together. OPENLED indicator Do not look directly at operating LEDs. flags if any string is left open. To improve efficiency, it is This circuit produces light that can damage eyes. recommended that V is between 3.1V and 5.5V. The IN NOTE: This document is for Demo Circuit 1327B. V bias capacitor of the demo circuit is rated at 6.3V. IN PWM dimming ratio can be as high as 3000:1. The soft Demonstration circuit 1327B is a 4-Channel 120mA LED start will not start until the 1st PWM pulse is presented. Driver with +/-1.5% Current Matching featuring the LT3599. The LT3599 is a step-up DC/DC converter de- The LT3599 datasheet gives complete descriptions of the signed to drive up to 4-strings of LEDs at an output volt- part, operation and application information. The data- age up to 44V. The LED strings are connected to internal sheet must be read in conjunction with this quick start current sources where the current level is set with an guide for working on or modifying the demo circuit external resistor. 1327B. The demonstration circuit drives 80mA through each LED string. Each string can have up to 10 white LEDs. Design files for this circuit board are available. Call The circuit operation frequency is set to 1MHz. Parame- the LTC factory. ters such as the LED current the switching frequency, L, LTC, LTM, LT are trademarks of Linear Technology Corporation. Other product names etc can be modified easily based on the demo circuit. may be trademarks of the companies that manufacture the products. When a string is not used, tie its LED pin to V . Any OUT unused string is no longer in the regulation loop. Direct PERFORMANCE SUMMARY Specifications are at TA = 25C SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS V Input Supply Range 3.1 5.5* V IN PV Power Input Supply Range** 8 16 V IN I Quiescent Current PWM=0V, Not switching 3 5 mA Q F Switching Frequency 0.9 1 1.1 MHz SW I LED String Current 77.6 80 82.4 mA LED I LED String Current Matching*** +/-0.25 +/-1.5 % M Eff Efficiency V = 3.3V PV = 12V I = 80mA 90 % IN IN LED D PWM dimming ratio PVIN = 12V 3000:1 PWM *: Limited by the voltage rating of the bypass capacitor, C3, on the demo circuit. The IC rating is 30V. **: PV below 8V causes current derating but the circuit operates fine. PV between 16V and 40V may be acceptable IN IN depending on the number of LEDs, desired LED current, etc. Power dissipation needs to be taken into considerations if PV is greater than the Maximum LED string voltage. IN ***: Specifications apply over the full operating temperature range. QUICK START PROCEDURE 1 LT3599 Demonstration circuit 1327B is easy to set up to evaluate 5. Turn on power supplies for VIN and PVIN. the performance of the LT3599. Refer to Figure 1 for 6. A PWM signal needs to be applied if PWM is not tied proper measurement equipment setup and follow the to VIN. procedure below: 7. If analog dimming is to be tested by varying the level 1. With power off, connect the input power supply to VIN of CTRL pin voltage, remove R15 to prevent triggering and GND. UVLO at low PVIN (<10V). 2. Connect the power input power supply to PVIN and 8. Removing R15 disables the programmed UVLO and GND. LED current derating. If those functions are required in 3. Tie PWM to VIN or a PWM signal. the test in 7, use two independent resistor dividers for UVLO and CTRL. 4. Connect LED strings to LEDn+ and LEDn-. If any string is not used, tie LEDn- to LEDn+, where n is the 9. Check for the proper LED voltage and current. string number (between 1 and 4). Figure 1. Proper Measurement Equipment Setup 2