L3751 DC converter reference solution

STMicroelectronics provides users with a reference design based on L3751, suitable for DC-DC converters with input voltage 36-72V DC, output voltage 12 VDC, and 10A. Download the reference design schematic below to view. The input stage components include bulk capacitors and filter circuits (C4, C5 and L1) that form a PI network to mitigate high-frequency radio emissions caused by high-frequency switching operations. The input DC bus voltage is connected to the VIN pin of the controller (pin 20) with a series resistor in the path. VIN powers the internal circuitry of the controller and also supplies the internal LDO regulator to generate a Vcc output voltage of 7.5V. VIN is also the power supply for the internal gate drivers. A small MLCC capacitor needs to be connected to pin 20. A bias voltage is applied to the enable pin (Pin 1) via an input voltage divider circuit to enable the controller at 40V to avoid deep discharge of the battery. Once the EN/UVLO pin voltage exceeds 1.2 V typical, the soft-start phase begins, the SS/TRK pin voltage rises, and the controller starts. In order for the controller to operate at a minimum input voltage of 40V, the values ​​of resistors R1 and R6 are chosen to be 100K and 4.7K respectively. To ensure that the control loop is absolutely stable and independent of capacitor type, the controller implements a Type III compensator, which provides developers with two zeros and three poles, ensuring that the phase margin is sufficient to improve performance at step loads.