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Associate II
October 12, 2026
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STDRIVE102BP power supply connections and internal LDO thermal considerations for a 24 V motor

Hello ST team,

I am designing a custom three-phase inverter using the STDRIVE102BP to drive a 24 V, 26 W BLDC motor. I would like to clarify the recommended external connections for VS, VCC, REGIN_3V3, and VDD.

I have reviewed the datasheet and the EVLDRIVE102BP schematic, but I am still confused about the power supply configuration.

  1. Are separate external 12 V and 3.3 V supplies required?

Do I need to supply VS with an external 12 V source and REGIN_3V3 with an external 3.3 V source?

Alternatively, if I use an external 3.3 V supply, should REGIN_3V3 and VDD be connected together to bypass the internal 3.3 V LDO? Does this bypass require any SPI configuration, or is it implemented entirely through the external connections?

  1. How is the evaluation board powered in its default configuration?

In the EVLDRIVE102BP schematic, REGIN_3V3 is connected to VCC through JP4, with pins 1–2 shorted by default.

VS appears to receive power from the external supply through the board’s connections. Initially, I interpreted this as a separate external 12 V supply. However, JP6 is shown as shorted by default, connecting VS to VM.

Could you confirm whether the default configuration supplies both VS and VM from the same motor power supply, with the internal LDO generating 12 V at VCC?

  1. What configuration does ST recommend for my application?

If a single external 24 V motor supply is sufficient, could you confirm whether the following connections are correct?

  • VM: connected to the external 24 V motor supply.

  • VS: connected to the same 24 V supply as VM.

  • VCC: used as the internal 12 V LDO output, with the required decoupling capacitor.

  • REGIN_3V3: connected to VCC.

  • VDD: used as the internal 3.3 V LDO output, with the required decoupling capacitor.

Please also advise whether any additional components or power sequencing precautions are recommended for this configuration.

Finally, I am concerned about heat dissipation when using both internal LDOs: 24 V to 12 V, followed by 12 V to 3.3 V.

For this 24 V, 26 W motor application, what criteria should I use to determine whether the internal LDOs can operate within their thermal limits? In particular, how should I account for MOSFET gate charge, PWM frequency, internal current consumption, and any external loads connected to VCC or VDD?

Under what conditions would ST recommend using an external supply for VS or REGIN_3V3 instead?

Thank you for your guidance.

Peter BENSCH
Peter BENSCHBest answer
ST Technical Moderator
October 13, 2026

A single 24V motor supply is usually sufficient for the STDRIVE102BP, provided the datasheet limits are respected.

Typical default setup on the eval board is:

  • VM and VS tied to the same motor supply
  • VCC generated internally at 12V
  • REGIN_3V3 linked to VCC by default
  • VDD generated internally at 3.3V

So, in the default configuration, separate external 12V and 3.3V supplies are generally not required.
If you use an external 3.3V rail, that is normally a hardware connection choice, not an SPI setting.

For your 24V, 26W BLDC application, the key thermal checks are the total current drawn from VCC and VDD, including:

  • IC quiescent current
  • gate-charge-related current
  • PWM frequency effects (gate charging power is proportional to the PWM frequency)
  • any external loads on VCC or VDD
  • ambient temperature

If the LDO power dissipation becomes too high, or board temperature rises too much, we would typically recommend using an external supply strategy instead of relying only on the internal LDOs.

For the hardware:

  • ensure that the required decoupling capacitors are present
  • pay attention to adequate grounding and a star-point concept
  • keep the VCC / VDD / bootstrap lines, and especially the gate-driver paths, as short as possible
  • minimise loads on VCC or VDD so that the internal LDO is not overloaded

For power sequencing, the usual order applies:

  • apply the motor supply when the system is to be enabled
  • allow the internal supplies to stabilise
  • then activate the driver

Hope that helps?

Regards
/Peter

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.
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1 reply

Peter BENSCH
Peter BENSCHBest answer
ST Technical Moderator
October 13, 2026

A single 24V motor supply is usually sufficient for the STDRIVE102BP, provided the datasheet limits are respected.

Typical default setup on the eval board is:

  • VM and VS tied to the same motor supply
  • VCC generated internally at 12V
  • REGIN_3V3 linked to VCC by default
  • VDD generated internally at 3.3V

So, in the default configuration, separate external 12V and 3.3V supplies are generally not required.
If you use an external 3.3V rail, that is normally a hardware connection choice, not an SPI setting.

For your 24V, 26W BLDC application, the key thermal checks are the total current drawn from VCC and VDD, including:

  • IC quiescent current
  • gate-charge-related current
  • PWM frequency effects (gate charging power is proportional to the PWM frequency)
  • any external loads on VCC or VDD
  • ambient temperature

If the LDO power dissipation becomes too high, or board temperature rises too much, we would typically recommend using an external supply strategy instead of relying only on the internal LDOs.

For the hardware:

  • ensure that the required decoupling capacitors are present
  • pay attention to adequate grounding and a star-point concept
  • keep the VCC / VDD / bootstrap lines, and especially the gate-driver paths, as short as possible
  • minimise loads on VCC or VDD so that the internal LDO is not overloaded

For power sequencing, the usual order applies:

  • apply the motor supply when the system is to be enabled
  • allow the internal supplies to stabilise
  • then activate the driver

Hope that helps?

Regards
/Peter

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.
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