STM32H7R3: Use SMPS to power a NOR flash chip, XSPI, and the MCU

EBDRS · ‎2024-07-16

My question today is kind of simple: I am using the SMPS to supply power to the MCU. Can I also use the SMPS to supply power to a NOR flash chip (W25 by Winbond, the exact chip doesn't matter, but it would be 1.8V with at least 64 Mbit size), and the XSPI I/O to communicate with the chip? Or would this use too much power? I cannot find any info on this.

EBDRS · ‎2024-07-17

>Or: are you asking using the SMPS in/on MCU and powering external stuff from it?
(not possible, not intended)

The question was using the SMPS on the MCU to supply power for external components. Due to the way one is supposed to implement the SMPS on an STM32H7R3 (AN5935 figure 2 on page 7), I assumed power could also flow to other external components, as long as they stayed under the 600 mA limit the SMPS has. Based on the STM32H7R3I8 datasheet, the max current consumption appears to be under the 600 mA limit, as long as it is not at 105 C with everything on. The XSPI uses 10 mA max, while the NOR flash would be 20 mA.

It appears that the SMPS is only on 1.8 V if it is not connected to Vcore. When connected to Vcore through the VCAP pins, it will make about 1.2 V. I would need to connect the SMPS to the LDO to get a 1.8 V output to use on other components.

>The SMPS on MCU is just for MCU (there is no way to get MCU to provide external power).

The SMPS does not connect internally, you have to connect it externally in order to power the MCU. According to AN5935, it can provide power externally, especially if the LDO is used to provide power to the MCU. However, you are not supposed to connect the SMPS to the VCAP in bypass; if one wants to use the SMPS to power both the MCU and external components, one would need to use the LDO, with either the SMPS or an external supply.

Solution edit: The SMPS can be used to power external components as it has an external connection, however it cannot be used to both power the MCU directly and external components. If one wants to use it to power external components and the MCU, it may be connected to the LDO, however the output current limit and the use by other components may degrade the signal. The best option if one wants to use the SMPS at 1.8V is to power the LDO by an external component, not the SMPS, and use the SMPS for the part. However, I do not know if this works.

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tjaekel · ‎2024-07-16

Are you asking how to use an external SMPS (chip) in order to power all the components on board?
Sure, why not.
All running at 1V8? or MCU with 3V3 and 1V8 for external SPI flash?

Bear in mind to set MCU VDD to 1V8 when using external 1V8 components (or level shifters needed). MCU runs at 1V8 but often still 3.0V needed for MCU.

So, you have to design an appropriate power supply circuit (e.g generating different voltages out from an input supply). Do you have a schematics?

Or: are you asking using the SMPS in/on MCU and powering external stuff from it?
(not possible, not intended)
The SMPS on MCU is just for MCU (there is no way to get MCU to provide external power). Was this your question?

EBDRS · ‎2024-07-17

>Or: are you asking using the SMPS in/on MCU and powering external stuff from it?
(not possible, not intended)

The question was using the SMPS on the MCU to supply power for external components. Due to the way one is supposed to implement the SMPS on an STM32H7R3 (AN5935 figure 2 on page 7), I assumed power could also flow to other external components, as long as they stayed under the 600 mA limit the SMPS has. Based on the STM32H7R3I8 datasheet, the max current consumption appears to be under the 600 mA limit, as long as it is not at 105 C with everything on. The XSPI uses 10 mA max, while the NOR flash would be 20 mA.

It appears that the SMPS is only on 1.8 V if it is not connected to Vcore. When connected to Vcore through the VCAP pins, it will make about 1.2 V. I would need to connect the SMPS to the LDO to get a 1.8 V output to use on other components.

>The SMPS on MCU is just for MCU (there is no way to get MCU to provide external power).

The SMPS does not connect internally, you have to connect it externally in order to power the MCU. According to AN5935, it can provide power externally, especially if the LDO is used to provide power to the MCU. However, you are not supposed to connect the SMPS to the VCAP in bypass; if one wants to use the SMPS to power both the MCU and external components, one would need to use the LDO, with either the SMPS or an external supply.

Solution edit: The SMPS can be used to power external components as it has an external connection, however it cannot be used to both power the MCU directly and external components. If one wants to use it to power external components and the MCU, it may be connected to the LDO, however the output current limit and the use by other components may degrade the signal. The best option if one wants to use the SMPS at 1.8V is to power the LDO by an external component, not the SMPS, and use the SMPS for the part. However, I do not know if this works.