Evaluation Board For Synchronous Buck Controller With PreBias Startup, And Optional Clock Synchronization
This application notes describes the LM2745 printed circuit board PCB design and provides an example typical application circuit. The LM2745 is a voltage mode PWM buck controller which implements synchronous rectification. It provides a low cost, high power density, and efficient point of load solution. In steady state operation the LM2745 is always synchronous, even at no load, thus simplifying the compensation design. The LM2745 ensures a smooth and controlled start up when the output is pre-biased. The current limit protection does not require a current limit resistor in the power path, but is achieved by sensing the voltage VDS across the low side MOSFET. Though the control sections of the IC are rated for 3 to 6V VCC, the driver sections are designed to accept input supply rails VIN as high as 14V.
**Specifics Of The Board** This demo board targets the fixed and mobile telecommunications, industrial electronics, and distributed power markets. The demo board has a VIN range of 8V to 14V and a LDO regulator, the LP2937, powers VCC by regulating a 5V output voltage. The LM2745 regulates to an output range of 1.2V to 3.3V at 19A with a switching frequency of 300 kHz. Note, the demo board is optimized for the above parameters, thus for additional design modifications refer to the Design Consideration section of the LM2745 data sheet. The PCB is designed on four layers, the top and bottom layers are 2oz. copper and the two inner layers are 1oz. copper. The board measures 2.19 in. x 1.03 in. x 0.41 in. 56 mm x 26.2 mm x 10.3 mm l, w, h on a FR4 laminate.