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I'm reading a circuit diagram, source http://bit.ly/1FAVXSw from P83 of book MASTERING STM32 SECOND EDITION Version 2.0.1 written by Carmine Noviello, a component is SB? like below:

circuit breaker first

I look it at BOM in Altium Designer, SB? is a circuit breaker:

circuit breaker senond

After reviewing the materials, I think it is a self-resetting fuse (perhaps my statement about self-resetting fuse is not accurate), which functions to disconnect the circuit to protect the chip when the current in that circuit momentarily increases.

I'm not sure if my understanding is correct, so I would like to consult with everyone.

Additionally, if what I mentioned above is correct, what specifications or models are typically used for this self-resetting fuse? Thank you.

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    \$\begingroup\$ @SamGibson Sorry for my poor English. bit.ly/1FAVXSw is provided by the book that author is carmine noviello, the link is written at P83 bottom of MASTERING STM32 SECOND EDITION Version 2.0.1, when you open above link to download the file, then link will let you go to st.com/resource/en/schematic_pack/nucleo_64pins_sch.zip \$\endgroup\$
    – Tom
    Commented Sep 6 at 11:41
  • \$\begingroup\$ Tom - Thanks for explaining. I don't know why the bit.ly link isn't working for me (it's possibly being blocked by corporate anti-malware etc.). Having the original link to st.com is probably better anyway :) \$\endgroup\$
    – SamGibson ♦
    Commented Sep 6 at 11:49
  • \$\begingroup\$ @SamGibson Can you access to st.com/resource/en/schematic_pack/nucleo_64pins_sch.zip \$\endgroup\$
    – Tom
    Commented Sep 6 at 11:55
  • \$\begingroup\$ Tom - Yes, thanks, I can access that st.com link. As I said, as a guess, the bit.ly link might be being blocked by the corporate anti-malware system here (some domains are deliberately blocked). \$\endgroup\$
    – SamGibson ♦
    Commented Sep 6 at 11:58

1 Answer 1

Reset to default
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The original source for that schematic, copied into the book you have mentioned, appears to be the MB1136 schematic for the ST Microelectronics Nucleo-64 STM32 development boards.

The reference designator "SB" = solder bridge. They are used for manually reconfiguring some functionality of the board.

The words "circuit breaker" you found in that BOM appear to be a mistranslation. A solder bridge can be used to break a circuit (i.e. a PCB track), but it's not a circuit-breaker, nor a self-resetting fuse.

Here is part of a page from STM32 User Manual UM1724, which is the user manual for the Nucleo-64 boards. It shows a list of the solder bridge assignments and functionality:

screenshot of part of STM32 UM1774 user manual

You can download the UM1724 PDF for the full list of solder bridges, if you need that.

FYI here the main ST Microelectronics STM32 Nucleo-64 product page. There is lots of useful info, especially using the "Documentation" (contains links to user manuals and other documents) and "CAD Resources" tabs (contains links to the schematics and Gerber files).

FYI for future readers: The Nucleo-64 boards which I've seen were manufactured with 0 ohm jumpers across SB pads, when that solder bridge is configured "closed" by default (this allows automated manufacturing and avoids a manual production step of soldering the required SB pads). The 0 ohm resistor can be removed to "open" that SB, when advised to do that in the user manual. That is discussed in this previous question: Remove 0 Ohm resistor (solder bridge jumper) There is a pair of solder pads underneath which can be shorted again in future with a blob of solder, if needed.

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  • \$\begingroup\$ I don't quite understand what you mean by "mistranslation." My understanding of "translation" is converting text from one language to another, such as translating Chinese into English. The ST Microelectronics Nucleo-64 STM32 development boards are provided by ST official sources. Could it be that the description of "SB?" was mistaken by ST? \$\endgroup\$
    – Tom
    Commented Sep 6 at 12:49
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    \$\begingroup\$ @Tom - Re: "Could it be that the description of "SB?" was mistaken by ST?" Personally, in this context, I doubt that :) I really do mean mistranslation is the likely cause here, IMHO. The words "circuit breaker" should have been spotted as incorrect terminology in this context, by a native English-speaking engineer. That leads me to conclude a language issue (i.e. mistranslation) is a likely reason for that mistake in terminology. Just to be clear, I'm suggesting the mistranslation occurred within ST, which is how it can appear within an official ST schematic's BOM. \$\endgroup\$
    – SamGibson ♦
    Commented Sep 6 at 13:49
  • \$\begingroup\$ Thank you for your further information. \$\endgroup\$
    – Tom
    Commented Sep 7 at 1:05

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