I checked PTN3356 reference design in data sheet and application note(AN11590).
And I have two questions about their reference design as below.
1. In Fig4 of the data sheet, VDD_3V3 and GND are connected by FB. But they are not used in Fig5.
- Are they OPTION DESIGN as ESD protection and PI filter?
- Are they necessary only for DC to DC converter mode?
2. In Fig4 and 5, VBUCK_1V5 is connected to GND by 4.7uF capacitor.
I think that it is smoothing capacitor for SWOUT.
Is it necessary for LDO mode? If it's necessary to both mode, could you tell me the purpose of it?