Introduction
Some STM32CubeMX users have noticed that the DIRECT_SMPS_SUPPLY option is not displayed when using certain STM32H7 dual-core part numbers, such as STM32H7x5 or STM32H7x7. This article addresses the question: Why is the DIRECT_SMPS_SUPPLY option unavailable in the RCC menu? Is it a limitation?
- Introduction
- 1. STM32CubeMX is not showing the DIRECT_SMPS_SUPPLY option
- 2. The reason why the direct SMPS option is not displayed in STM32CubeMX
- Conclusion
- Related links
1. STM32CubeMX is not showing the DIRECT_SMPS_SUPPLY option
As illustrated in figure 1, the SMPS (PWR_DIRECT_SMPS_SUPPLY) power configuration option is not displayed, while LDO (PWR_LDO_SUPPLY) and other power configurations are available. This may appear to be a bug or limitation in STM32CubeMX to the user. However, this is not the case.
2. The reason why the direct SMPS option is not displayed in STM32CubeMX
Let us use the STM32H755 as an example. According to the datasheet of the STM32H7 MCU:
The Voltage Scale 0 (VOS0 - boosted performance) is available only with the LDO regulator, as shown in Figure 2 below.
The Boosted performance refers to a system frequency greater than 400 MHz, where VOS0 (Voltage Scale Level 0) must be used. As illustrated in figure 3, the maximum frequency supported with VOS1 is 400 MHz.
If the system frequency is configured to exceed 400 MHz, STM32CubeMX automatically sets the voltage scale to VOS0 and disables the DIRECT_SMPS_SUPPLY option by hiding it. To enable this option, set the system frequency to a value less than or equal to 400 MHz. Figure 4 demonstrates the DIRECT_SMPS_SUPPLY option displayed in STM32CubeMX.
For instance, if you are using the NUCLEO-H755 board, the maximum frequency allowed with this board is 400 MHz, as the default power supply configured by hardware is SMPS. To achieve the maximum frequency of 480 MHz, you must modify the hardware configuration on the board to operate in LDO mode. Refer to the board’s schematic for details on the required modifications. Figure 5 illustrates the changes needed to switch the NUCLEO-H755 board to LDO mode.
Ensure that the correct power supply is configured according to the board’s power setup. Otherwise, the MCU may become locked. In such cases, follow the procedure to unlock the MCU.
Refer to this knowledge base article:
How can I recover my STM32H7/STM32H7RS board after facing a power configuration deadlock?
Conclusion
This article explains why the DIRECT_SMPS_SUPPLY option is not displayed in STM32CubeMX. The absence of this option is due to the system frequency selected by the user, which exceeds 400 MHz. To enable the DIRECT_SMPS_SUPPLY option, set the frequency value to 400 MHz or lower in STM32CubeMX.
