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