DEMO CIRCUIT 1327B QUICK START LT3599 GUIDE LT3599 4-Channel 120mA LED Driver with +/-1.5% Current Matching DESCRIPTION WARNING! Do not look directly at operating LEDs. This circuit produces light that can damage eyes. NOTE: This document is for Demo Circuit 1327B. Demonstration circuit 1327B is a 4-Channel 120mA LED Driver with +/-1.5% Current Matching featuring the LT3599. The LT3599 is a step-up DC/DC converter designed to drive up to 4-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 resistor. The demonstration circuit drives 80mA 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 current per string is allowed. To paralleling strings, tie the respective LEDn pins together. OPENLED indicator flags if any string is left open. To improve efficiency, it is recommended that VIN is between 3.1V 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 soft start will not start until the 1st PWM pulse is presented. The LT3599 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 1327B. 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 3.1 8 PWM=0V, Not switching 0.9 77.6 VIN = 3.3V; PVIN = 12V; ILED = 80mA PVIN = 12V TYP 3 1 80 +/-0.25 90 3000:1 MAX 5.5* 16 5 1.1 82.4 +/-1.5 UNITS V V mA MHz mA % % *: Limited by the voltage rating of the bypass capacitor, C3, on the demo circuit. The IC rating is 30V. **: PVIN below 8V causes current derating but the circuit operates fine. PVIN between 16V and 40V may be acceptable depending on the number of LEDs, desired LED current, etc. Power dissipation needs to be taken into considerations if PVIN is greater than the Maximum LED string voltage. ***: Specifications apply over the full operating temperature range. QUICK START PROCEDURE 1 LT3599 Demonstration circuit 1327B is easy to set up to evaluate the performance of the LT3599. 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. 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 4). 5. Turn on power supplies for VIN and PVIN. 6. A PWM signal needs to be applied if PWM is not tied to VIN. 7. If analog dimming is to be tested by varying the level of CTRL pin voltage, remove R15 to prevent triggering UVLO at low PVIN (<10V). 8. Removing R15 disables the programmed UVLO and LED current derating. If those functions are required in the test in 7, use two independent resistor dividers for UVLO and CTRL. 9. Check for the proper LED voltage and current. Figure 1. Proper Measurement Equipment Setup 2 LT3599 3