STSPIN32G4 with motor voltage of 6V

[jcysyk]

I want to use the STSPIN32G4 for an application with a motor voltage of 6-8V.  Has anyone ever ran with this low of a motor voltage. The specifications list the minimum motor voltage of 5.5V, so I believe it should be possible.  However, the lowest buck voltage (VCC) setting is 8V.  What will VCC be if Vm is 6V?  I believe I will have to drive VCC directly, instead of using the buck converter.  Can I tie Vm directly to VCC for this application?

[RhSilicon]

DS13630

• Table 8. VCC Buck regulator output voltage

Apparently this regulator only serves to polarize the (Gate) switches (MOSFET), not to power the motor (VM).

5.1 Power management section: The VM pin is the main supply voltage of the device

5.1.1 VCC buck regulator
The device integrates a buck regulator generating the supply voltage for the gate drivers (VCC) starting from the
motor supply (VM). The regulated voltage supplies the gate driving circuitry, charges the bootstrap capacitors and
supplies external circuitry with a maximum overall consumption of 200 mA.

2.2 Recommended operating conditions: VM pin (5.5V~75V)

See Figure 26. Application example diagram. The application schematic is very confusing, but there is a trial board (EVSPIN32G4NH), check the schematic, VM comes from CN2 connector:

https://www.st.com/en/evaluation-tools/evspin32g4nh.html

[RhSilicon]

Note: The schematics are in a different tab (to confuse users a little more)

https://www.st.com/en/evaluation-tools/evspin32g4nh.html#cad-resources

[jcysyk]

Thanks for the response.  Yes, the buck-converter is only used for the gate drivers.  The lowest setting for the buck-converter is 8V, but I'm not sure what will happen if I drive it with 6V - a lower stable buck voltage, and unpredictable voltage, or nothing?  There is an option to drive VCC directly and not use the buck converter.  So will I be OK connecting VCC directly to VM?  The eval board has VCC tied directly to the buck-converter so I cannot test this out.  For my custom layout I think I will put in solder bridges for the option of using the buck-converter or driving VCC directly.  Unless there's something else I'm missing

[RhSilicon]

See Figure 7. VCC externally supplied (buck disabled) - DS13630

• It is possible to provide externally the VCC supply, bypassing the integrated regulator

[jcysyk · Accepted solution]

So to close out this thread, for anyone else interested in running at 6V.  Using the eval board (STSPIN32G4NH) I varied the motor voltage and measured VCC

Vm [V]	VCC (buck) [V]
12	10.5
11	9.6
10	8.7
9	7.8
8	6.9
7	6.0
6	4.9	motor control failed
6	6 (tied to Vm)	motor ran

Motor ran down to 7V, but failed at 6V.  I assume because VCC dropped below the minimum of 5.5V.  If I tied Vm directly to Vcc at 6V, the motor ran fine.