The STM32U3 is now available! - Page 1
Forum section: electronics / general

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 06, 2025, 11:10:14 am
content: https://www.st.com/en/microcontrollers-microprocessors/stm32u3-series.htmlIn stock too (although stocks look limited for now).As a reminder, they have 256KB RAM, 512KB or 1MB Flash, I3C and they are supposed to be the first subthreshold MCUs from ST.The power consumption figures look good but a bit disappointing. I was expecting better. Ambiq does better.- Power consumption in Stop modes is similar to the U5, and good but not extraordinary. Similar to the U5.- In "run" mode, the figure @96 MHz is almost the same as the U5 (16 µA/MHz). It goes down to 13 µA/MHz @48 MHz and 9.5µA/MHz (which is admittedly the lowest figure for any ST MCU at the moment, but still higher than Ambiq ones, but the datasheet doesn't specify the clock frequency...)They aren't cheap either. So, kinda disappointed at this point. I'll stick to the U5.

author: BadeBhaiya
author_rank: Regular Contributor
timestamp: March 07, 2025, 11:58:13 am
content: Loads of flash, lot of RAM, low power and a lot of IOs. No RF. LQFP100 package looks delicious. Only 96MHz.I'm confused, who is the target market for this? Maybe applications where GUIs need to be driven perhaps?

author: woofy
author_rank: Frequent Contributor
timestamp: March 07, 2025, 12:13:01 pm
content: STM describe the U3 as "near-threshold CMOS", rather than "sub-threshold"https://blog.st.com/stm32u3/And some info on the difference:https://www.techdesignforums.com/practice/guides/subthreshold-near-threshold-computing-logic-ntv/I guess they need just a little energy to get to 96MHz.

author: uer166
author_rank: Super Contributor
timestamp: March 08, 2025, 03:04:32 am
content: Currently using a U5 for a handheld device, this one would also be perfect for it for extreme low power but also enough oomph to drive a GUI.

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 08, 2025, 12:15:14 pm
content: Quote from: woofy on March 07, 2025, 12:13:01 pmUh huh, ahh, marketing!https://www.eevblog.com/forum/microcontrollers/stm32u3-announced/They did announce it as a subthreshold MCU. I didn't make that up.Guess they got bitten and changed their mind.

author: vaualbus
author_rank: Frequent Contributor
timestamp: March 11, 2025, 11:53:35 pm
content: Cool product we had a meeting with ST, with a client, regarding this early in the year because they wanted to suggest the use of it for a product.It has some cool things but maybe they have not included all of what they told us.I don't know I have still to read all the reference manual (I mean the chapter title of curse, I am not mad) to see what new features it has.At the end we didn't use it to risky to use new silicon and, as far as I know, U3 still do not support the linked list DMA mode that is a juice feature of U5 and WBA chips.

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 12, 2025, 12:16:06 am
content: I read the datasheet closely and as I said, I'm a bit disappointed.- The run mode consumption is barely better than the U5 (depends on frequency). Look closely at the tables for it in both datasheets, you may be surprised. At some frequencies, the U5 actually draws less current. The 9.5 µA/MHz figure is only for very specific conditions.- In low-power modes (stop/standby), it's basically identical to the U5.- The U3 doesn't seem to have LPBAM (unless I missed it), which is a big plus for the U5 when in Stop mode.- Pricing doesn't seem much lower than the U5.So, I see no point personally for the U3 at this point compared to the U5, but let's see how it turns out and what kind of models they release (I think the U3 series has only 2 models for now).

author: vaualbus
author_rank: Frequent Contributor
timestamp: March 12, 2025, 06:48:28 am
content: Well they have something new new I guess like better HW 'security' and I3C if anyone cares about itBut overall I think you need to think where it is placed in the marked. It is between the U0 and L4; U0 is very cheap but has almost no RAM and ROM to work with and was developed, probably, for water smart metering. Doing anything more on U0 is challenging due to the low memory size.

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 12, 2025, 11:29:40 am
content: Quote from: vaualbus on March 12, 2025, 06:48:28 amBut look at the pricing. The STM32U375 is ~ $3.07 / 1000, the STM32U535 is ~ $3.22 / 1000. I mean, yeah. If you really need I3C (which is still not really widely used) and don't care for LPBAM, maybe.A bit puzzled at the pricing strategy here, but maybe prices for the U3 are still not "final", I don't know.

author: tszaboo
author_rank: Super Contributor
timestamp: March 12, 2025, 02:44:25 pm
content: I've just seen this demoed at the embedded world. The micro was running at 24MHz, which is the sweet spot for power efficiency, and it was only using 0.3mA current. This is quite good IMHO, even if it is not record breaking, but very good nevertheless.Quote from: SiliconWizard on March 12, 2025, 11:29:40 amI've learned to ignore ST's prices at Digikey or Mouser.

author: utroiscpasmal
author_rank: Newbie
timestamp: March 14, 2025, 06:45:16 pm
content: Quote from: SiliconWizard on March 06, 2025, 11:10:14 amWhere did you find the U5 @96MHz ? I see only 72MHz or 110MHz in U5 datasheet.My calculation is giving 57uA/MHz (@72MHz) higher than 16uA/MHz for U3.

author: utroiscpasmal
author_rank: Newbie
timestamp: March 14, 2025, 10:12:24 pm
content: Quote from: SiliconWizard on March 06, 2025, 11:10:14 amSomeone did calculation on Ambiq numbers :https://www.reddit.com/r/embedded/comments/rhtghn/ambiq_apollo4_mcu_realworld_power_consumption/?rdt=58402Here below mine :1. From Ambiq datasheet, table.23 :https://contentportal.ambiq.com/documents/20123/1730118/Apollo4-Lite-Datasheet.pdf2. Value at 1.9v (since the product cannot work at 3.3v) = 19.2µA/MHz3. Ambiq Apollo4 is a Cortex-M4, STM32U3 is a Cortex-M33 (20% more performant)4. From STMicro datasheet, table.32 :https://www.st.com/resource/en/datasheet/stm32u385cg.pdf5. At 48MHz STM32U3 consumes 1mA @1.8v = 20.8µA/MHz6. Not comparing the same frequency, but putting each product at its best efficiency (96MHz for Ambiq / 48MHz for STMicro)7. To compare different core, different voltage and different frequency, we can measure the power to execute a CoreMark --> CoreMark/mW8. Ambiq Apollo4 Cortex-M4 performs 3.46 CoreMark/MHz --> 332 CoreMark @96MHz9. STM32U3 Cortex-M33 performs 4.09 CoreMark/MHz --> 196 CoreMark/MHz @48MHz10. Apollo4 number = [3.46 CM/MHz x 96MHz] / [19.2µA/MHz / 1000 x 96MHz x 1.9v] = 94.9 CoreMark/mW11. STM32U3 number = [4.09 CM/MHz x 48MHz] / [20.8µA/MHz / 1000 x 48MHz x 1.8v] = 109.2 CoreMark/mW12. STMicro claims 117 CoreMark/mW on his websiteMy calculation gives 15% better efficiency for STM32U3 vs Ambiq Apollo4

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 17, 2025, 08:54:15 pm
content: Quote from: utroiscpasmal on March 14, 2025, 06:45:16 pmI may have been too quick at drawing conclusions based on confusing figures and took the best cases in the front page a bit too optimistically.To make things clear first, I'm considering both running @3.0V and on SMPS.So yes, turns out there's a pretty significant difference @96 MHz (1.65 mA for the U375, no direct figure for the U535, but we can interpolate something about 4 mA, so that's pretty significant indeed).Things become less pretty at lower frequencies. For instance, @1 MHz, the U3 draws 0.12 mA vs. 0.10 mA for the U5.And the absence of LPBAM, along with Stop mode consumption approx. identical to the U5, makes the U3 a lot less interesting if most of the time is spent in Stop mode (and you have use cases for LPBAM, which I do in one critical project!)Still, the power savings look more significant that I thought in run mode. So, again all depends on your use cases.As to the Ambiq MCUs, I have experience with the Apollo 3 on which I'd get better figures up to 48 MHz than the U3. But no experience with the Apollo 4 (which is supposed to have lower consumption/MHz than the Apollo 3, but of course it's marketing figures and reality will tell a different story; also it's a "much" more featureful MCU than the U3, pretty large memory, so I don't know how fair the comparison is with it.)I'll probably have a go with the U3 to see if I get better results than with the U5 in my use cases.

author: elektryk
author_rank: Regular Contributor
timestamp: March 18, 2025, 12:12:37 pm
content: Quote from: tszaboo on March 12, 2025, 02:44:25 pmSo where do you get them?

author: tszaboo
author_rank: Super Contributor
timestamp: March 18, 2025, 12:28:10 pm
content: Quote from: elektryk on March 18, 2025, 12:12:37 pmArrow, Avnet sells global, or local smaller distributors. You ask a quote or start already negotiate pricing.People who pay a full price for a full reel don't understand electronics procurement.