DEMO CIRCUIT 975 QUICK START LT3482 GUIDE LT3482 DC/DC Boost Converter for APD Bias DESCRIPTION Demonstration circuit 975A is a DC/DC Converter for APD Bias featuring the LT3482 in a 3mm x 3mm QFN package. This demo circuit is designed to convert a 3V-12V source to 80V at 2mA. The circuit runs at 1.1MHz but can be easily programmed to run at 650KHz (inductor and other components might need to change for such case). The LT3482 features a 48V, 260mA switch, integrated Schottky diodes and a high side current monitor which provides a current proportional to the APD current. This current can be used as a reference to digitally program the output via the CTRL pin. This circuit is specifically designed for APD bias and is optimized for performance, solution size and profile. To further reduce the solution size, inductors such as Taiyo Yuden BRL2012B type can be used though efficiency will suffer about 10%. Typical applications include APD bias, PIN Diode Bias, Optical Receivers and Modules, Fiber Optic Network Equipment etc. Design files for this circuit board are available. Call the LTC factory. LT is a registered trademark of Linear Technology Corporation. PERFORMANCE SUMMARY DC975A SYMBOL VIN VOUT VOUT RIPPLE FS PARAMETER Input Supply Range Output Voltage Range Output Voltage Range Switching frequency Specifications are at TA = 25°C CONDITIONS VIN = 3V, ILOAD = 2mA VIN = 12V, ILOAD = 2mA VIN = 3.6V, ILOAD = 2mA MIN 3 75 75 TYP 80 80 500 1.1 MAX 12 85 85 UNITS V V V µV MHz QUICK START PROCEDURE Demonstration circuit 975 is easy to set up to evaluate the performance of the LT3482. Refer to Figure 1. for proper measurement equipment setup and follow the procedure below: NOTE. When measuring the output voltage ripple, use a BNC cable to connect J1 to the oscilloscope. Set the oscilloscope to AC couple, 2mV/division. That should yield the results shown in Figure 2 (Make sure there are no test cables connected to the APD node). 1. Place jumper in the following position: JP1 Run 2. With power off, connect the input power supply to Vin and GND. 3. Connect a 40K resistor from APD to GND. 4. Turn on the power at the input. 5. Check for the proper output voltage. Vout1 = 75V to 85V. NOTE. If there is no output, temporarily disconnect the load to make sure that the load is not set too high. 6. Once the proper output voltage is established, adjust the load within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. 1 LT3482 Figure 1. Proper Measurement Equipment Setup 2 LT3482 Figure 2. Output Ripple measured with BNC cable directly connected to oscilloscope. BW=20MHz. 2mV/div 3 LT3482 4 LT3482 5