8.3 Freewheeling Diode

The MCP16367/8/9 requires a freewheeling diode to create a path for the inductor current flow after the internal switch is turned off. The diode must have a reverse voltage rating greater than the maximum input voltage possible in the application. The peak current rating of the diode must be higher than the maximum inductor current. The lower the forward voltage of the diode, the higher the efficiency of the regulator, and that is why Schottky diodes are typically a good choice for this purpose.

On the other hand, the diode must also be selected with an appropriate power rating. The diode conducts the output current during the off-time of the internal power switch, and, therefore, in high V_IN to V_OUT ratios, the conduction losses of the diode may become significant. The conduction 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.