3.4 Buck Converter Guidelines and Considerations
A buck converter is implemented to power the core at a lower voltage. The buck allows for reduced power loss and heat generated within the device. The connections are:
- SWVDD – This power pin is connected to the internal power switches of the buck converter. This pin has high transient currents and should have a low impedance path to VDD. A 10 µF (4.7 µF minimum) capacitor is recommended as close as possible to the pin.
- SWVSS – This power pin is connected to the internal power switches of the buck converter. This pin has high transient currents and should have a low impedance path to PCB ground.
- LX - This pin is the output of the H bridge power switches and provides current to the external inductor. This pin has high transient currents and should have a low impedance trace to the inductor.
- VDDCORE – This pin supplies power from external inductor to the core. A 10 µF capacitor is required and should be placed as close to the VDDCORE pin and inductor as possible.
The buck converter adjusts duty cycle to maintain a constant voltage output as the current demands change. Current is delivered to the core through the external inductor and is filtered with the capacitor in the VDDCORE pin. Figure 3-1 illustrates a simplified topology of the buck components inside the dsPIC®.
No other connections should be made to the VDDCORE or LX pins. The output voltage of the buck converted is listed in Electrical Characteristics. An example application circuit is shown in Figure 3-2.