8.3 Freewheeling Diode

The MCP16367/8/9 requires a freewheeling diode to create a path for the inductor current flow when the internal switch is turned off. The diode must have a reverse voltage rating greater than the maximum input voltage expected in the application. Additionally, its peak current rating must be higher than the maximum inductor current. A diode with a lower forward voltage drop increases the efficiency of the regulator, which is why Schottky diodes are typically recommended for this application.

It is also important to ensure that the diode has an adequate power rating. During the off-time of the internal power switch, the diode conducts the output current. In applications with a high V_IN to V_OUT ratio, diode conduction losses can become significant. These losses can be estimated using Equation 8-3.

Equation 8-3. Diode Conduction Losses

P_{D} = \frac{(V_{I N} - V_{O U T}) \times I_{O U T} \times V_{F W}}{V_{I N}}

Where:


I_OUT	=	Nominal output current
V_OUT	=	Output voltage
V_IN	=	Input voltage
V_FW	=	Forward voltage drop of the diode

Because of the high switching frequency, the AC losses of the diode must also be taken into account. These losses are caused by the charging and discharging of the junction capacitance and the reverse recovery charge.