STSPIN32G4 separate control and motor supplies

[OscarM]

I developed a board for 3 ph motor control with a quadrature encoder that seems to work fine. Now my client would like to modify it to use separate supplies for control/logic and motor as is standard practice in the PLC/automation world.

There are a couple of ways of doing this (in order of preference):

1) Power the STM32G431 die from the logic supply and the drive die and motor from the motor supply

2) Power the STSPIN32G4 from the logic supply and the motor from the motor supply.

3) Treat everything associated with the STSPIN32G4 and motor as a 'motor power domain' (not preferred)

Thinking about approach #1:

Figure 1 on page 3 of the data sheet is not super helpful.

It shows VDD on both dies without a strong indication of how it gets from one to the other.

Perhaps they are separate, one coming in on the VDD/VDDA pin of the left hand die and another one coming in on REG3V3/VDD of the right hand die because they are actually different nets?

Power sequencing becomes a consideration.

Has anyone done this/considered this or developed recommendations ?

[Brohanlo]

I am also interested in finding an answer for this.

1) is preferred because then the STM32G431 and its associated components can operate from a PELV/SELV power source.

However 3) seems to be the only way to truly isolate the motor supply from the rest of the low-voltage circuitry.

[Cristiana SCARAMEL]

Hello @OscarM and welcome to the ST Community.

The STSPIN32G4 allows a flexible selection of power supplies depending on application requirements.

One point that must be highlighted is that both STM32G431 microcontroller and gate driver die requires a logic supply voltage in the 3.3 V domain.
This supply corresponds to pin 1 named REG3V3/VDD that is internally connected to both microcontroller and gate driver so there is no possibility to use separate independent voltages as assumed in point 1.

However the 3.3 V supply can be provided via an external regulator instead of the internal LDO regulator. 
The recommended way is described in Figure 12 of the datasheet where REGIN and REG3V3 pins must be shorted together and connected to the external regulator.
This approach can be useful when the control logic supply rail is always on, while the motor supply voltage can be turned off when motor is not spinning.
In this case the microcontroller remains operative while the gate driver is disabled and no I2C access is possible too.

Pin 27 is the VDDA supply of analog subsystems like ADC and DAC inside the microcontroller and it is independent from control logic supply REG3V3/VDD.
Refer to STM32G431 datasheet for allowed voltage levels. Commonly VDD and VDDA nets are shorted together at board level or a ferrite bead is inserted between them.

Regarding the gate driver voltage VCC it is usually derived from the main motor voltage via the integrated buck converter. If an external regulator is needed for this VCC rail the preferred connection is illustrated in Figure 7 of STSPIN32G4 datasheet where the VM and SW pin are shorted together.

With above considerations points 2 and 3 are both viable and alternatively used in STSPIN32G4 applications.