TMS320F28379D: TMS320F28379D

Hello
I made an inverter circuit to be controlled with TMS320f28379 and TMS ... 069M. I used Ps21767 Mitsibushi IPM for this inverter circuit.
Since the PS21767 module has HVIC technology, PWM can be given directly from the MCU, it says in the application note.
The LVIC driver circuit control voltage of the IPM module is +15 V DC and the bootstrap circuit is used for the HVIC.
5V DC is required for fault output (Fo). Some Texas ins. He mentions two options for supplying control circuit power in HV motor control development kits.
In the form of using an external power supply or 15V/5V source from the DC bus for the control voltage. If I use an external source (15V), it says that I need to combine the GND (Control GND) of
this source and the GND (Power GND) of the DC bus from a single point (mitsibushi PS21767 IPM app. Note). What I want to ask is how should the GND plan be in such high DC voltage applications?
It is necessary to use 15 V external auxiliary source isolation (eg meanwell IRM-10-15).
Or should it be obtained from the DC bus by voltage division method and regulated at 15 volts (GNDs are the same) and used (for example, with Viper26).
Also, if I use an external power supply, can I feed the DSP(TMS…379D) with 15V -5V/3.3V with this power supply?
Would it be a problem for the DSP if the GNDs are the same? What I'm really curious about is how should the GND plan be in such applications?