2022-09-22 12:43 AM
2022-09-24 02:24 AM
From your other posts I see you use the 'U5xx, so I took a look at the 'U575 DS.
In Functional overview/VREFBUF chapter, there's a schematics with capacitor with no marking, so that may be the first clue.
In Electrical characteristics/VREFBUF chapter/table the capacitor is specified, and in fact in a rather narrow range, min.0.5uF typ.1uF max.1.5uF, with a footnote requiring an additional 100nF HF bypass. Then later in the table, the startup time is given as function of the actual cap used.
But I agree that this all is fineprint too easy to miss when designing a board, being overwhelmed by all the many detailed requirements.
Thanks for this post.
JW
[EDIT] I've had a look also at the 'L0/'L1 DS. These two families are relative outliers in several respects from other STM32, and in this particular respect, they have a buffered VREFINT (the buffered version called VREF_OUT), connectable to two GPIO pins, for whatever purpose. Granted, it has only 1uA current capability, as compared to VREFBUF's 4mA, and no direct connection to VREF+. Nonetheless, the DS for this VREF_OUT calls for *max* 50pF output load. If you'd had experience with this feature in the past, it's just natural then to tend to expect the similar with VREFBUF.
@Peter BENSCH , see here potential for one of those dozens of appnotes per peripheral I'm talking about all the time?
2022-09-26 12:53 AM
Thank you @Community member for bringing this to our attention. There is certainly room for improvement in the appnotes.
@Imen DAHMEN
@Amel NASRI
2022-09-27 06:49 AM
Hello @Community member,
Thank you for your feedback.
As I understand the request is to improve the following topics:
Could you please clarify this?
With Regards,
Mohamed Aymen
2022-09-27 01:57 PM
Hi Mohamed Aymen,
Yes, you're absolutely right, in both points.
Note, that there are STM32 families ('L0, 'L1) which do have a genuine VREF_OUT signal, so don't change those.
What exactly would you need to clarify further?
Thanks,
Jan
@Mohamed Aymen HZAMI
2022-09-30 02:55 AM
Hi @Community member,
What do you mean by:
>Note, that there are STM32 families ('L0, 'L1) which do have a genuine VREF_OUT signal, so don't change those.
Mohamed Aymen
2022-09-30 11:48 AM
Hi Mohamed Aymen,
In the 'L0 and 'L1 families, which are older, and don't have the VREFBUF module, the internal VREFINT module - which is present in all STM32 but in the vast majority its entirely internal and has no outside connection - but in 'L0 and 'L1 VREFINT can optionally be output to certain pins. This is marked as VREF_OUT and this should not be changed.
The VREFBUF module is relatively new, first appeared in the 'L4 family.
It's output is connected directly to VREF+ pin, but if it needs to be indicated in the datasheet, it ought to be called VREFBUF_OUT and not VREF_OUT. So VREF_OUT is incorrect only in the STM32 models which are newer than 'L4 and do have VREFBUF (as in 'G071:
)
JW
@Mohamed Aymen HZAMI
2022-10-03 02:31 AM
Hello @Community member,
Thanks for the clarification.
Mohamed Aymen