SLVS839F July 2008 – October 2014 TPS54331
The TPS54331 device is designed to operate using an external catch diode between the PH and GND pins. The selected diode must meet the absolute maximum ratings for the application. The reverse voltage must be higher than the maximum voltage at the PH pin, which is VIN(MAX) + 0.5 V. The peak current must be greater than IOUT(MAX) plus half the peak-to peak-inductor current. The forward-voltage drop should be small for higher efficiencies. The catch diode conduction time is (typically) longer than the high-side FET on time, so attention paid to diode parameters can make a marked improvement in overall efficiency. Additionally, check that the selected device is capable of dissipating the power losses. For this design, a Diodes, Inc. B340A was selected, with a reverse voltage of 40 V, forward current of 3 A, and a forward-voltage drop of 0.5 V.