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While reading a datasheet for an IC I came across the pin voltages being presented as 3V3 or 1V8. What does this representation stand for?

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    \$\begingroup\$ my guess would a 3.3 volt rail and a 1.8 one. \$\endgroup\$
    – kenny
    Commented Mar 14, 2012 at 19:26
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    \$\begingroup\$ So many possible duplicates: electronics.stackexchange.com/questions/246920/… \$\endgroup\$
    – user107801
    Commented Aug 9, 2016 at 10:16
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    \$\begingroup\$ However this question is much unique because it asks voltage. others seek resistance. \$\endgroup\$
    – user107801
    Commented Aug 9, 2016 at 10:22
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    \$\begingroup\$ Wikipedia tells : The European notation BS 1852 avoids using a decimal separator ... problem that decimal separators tend to "disappear" when photocopying a printed circuit diagram. en.wikipedia.org/wiki/Resistor#Electronic_symbols_and_notation . However that-page is about resistors. \$\endgroup\$
    – user107801
    Commented Aug 9, 2016 at 10:23

4 Answers 4

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That's the new politically correct way of writing numbers that would normally have decimal points. Some parts of the world (Germany for example) use a comma to separate the integer and fraction digits. To avoid ambiguity in international situations, some people now put the letter for the units where the decimal point should be. So "3V3" really means 3.3 Volts and "1V8" means 1.8 Volts.

If your audience is English speaking or it is obvious the document or the context is in English, then you are fine using a decimal point normally. After all, using a decimal point is part of the language no less than the words used to describe other things, so this is not ambiguous. In rare cases when numbers are by themselves without a language context, then it's probably best to use the "3V3" type notation. Otherwise, I personally find this notation rather annoying since I have to look at it and think about it rather than the brain parsing it without much conscious thought.

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    \$\begingroup\$ You will also see it a lot with resistor values. i.e. 4k7 is 4.7Kohm. \$\endgroup\$ Commented Mar 14, 2012 at 19:35
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    \$\begingroup\$ 3V3 is also shorter than 3.3V \$\endgroup\$
    – Pentium100
    Commented Mar 14, 2012 at 20:00
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    \$\begingroup\$ It's worth noting that I've had some problems in SPICE simulations with the "." character in net names (Well, I think it was "." chars, I removed them and it fixed the problem). Using "3v3" or "1v8" is an easy way to clearly describe the voltage while restricting net names to exclusively alphanumeric characters. \$\endgroup\$ Commented Mar 14, 2012 at 21:37
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    \$\begingroup\$ This notation is neither new (I know if for at least 25 years) nor is it because of the existence of different decimal separation characters. It's for clarity when values are printed on tiny electronic devices like Z-diodes (it's a big difference if its value is 3.3V or a 33V). I think it's just a bad habit that this notation is used also in documents. \$\endgroup\$
    – Curd
    Commented Mar 15, 2012 at 10:47
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    \$\begingroup\$ Surely a 0.00025Ω resistor would have considerably less resistance than many of the PCB traces in the circuit. It would be essentially indistinguishable from a 0Ω resistor (which to my knowledge are just called "zero ohm resistors".) \$\endgroup\$
    – LeoR
    Commented Jan 24, 2014 at 10:09
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I've always been told that the reason for using letters or symbols in place of the decimal point is neither for international relations or variable names in code but for clarity in print. The issue being that when datasheets were typed up, or schematics drawn, and then copied/photocopied/faxed/etc the dot may get dropped.

This issue obviously isn't such a big deal these days but using 3V3 or 4R7 is still pretty common. It's really common in older documentation here in the UK (and I'm talking back to kind of era where we really wouldn't have creating documents with legibility to Germans in mind...).

I'm pretty happy transposing commas for full stops in European documents, it's fairly common to find them in European publications (even when they've been translated to English).

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    \$\begingroup\$ I think avoiding that the decimal point might get dropped is the main reason. Especially when values are printed on tiny electronic devices, e.g. Z-diodes. Suppose "3.3V" would be printed on a small 1x2mm cylinder. It could be misstaken for "33V". \$\endgroup\$
    – Curd
    Commented Mar 15, 2012 at 10:40
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    \$\begingroup\$ Example: electronicrepairguide.com/images/zener%20diode%20datasheet.jpg \$\endgroup\$
    – Curd
    Commented Mar 15, 2012 at 11:28
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It's a naming convention to denote voltages. The period is replaced by the V. So, rather that 3.3V or 1.8V you would write 3V3 and 1V8, respectively. It came about for a couple of reasons:

  • In schematics which involve a device for which code has to be written (microcontroller, FPGA), many code languages use a period or comma as an operator (for example C uses periods to reference structure members). If this is the case, the names of the signals in the code cannot directly follow the schematic net names to which they are connected as it will cause compilation errors. So this scheme was developed to get around this and allow the exact same net to be referenced in the code as in the schematic, allowing for easier readability of the code and a more accurate reflection between the code & schematic.

  • For the reason mentioned above, many schematic editors don't accept periods or commas in the names of the nets because they generate code directly from the schematics or use code to operate directly on the schematics. Both cases can be corrupted by the use of symbols (like periods or commas).

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    \$\begingroup\$ Point 1 sounds like a weak argument since most languages won't let you create symbols starting with a digit. \$\endgroup\$ Commented Mar 14, 2012 at 20:33
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    \$\begingroup\$ @OlinLathrop It still could work if your voltage indication is after another name, which is likely (e.g. SetOutput_3V3), where in C code the period would result in a structure type. \$\endgroup\$
    – clabacchio
    Commented Mar 15, 2012 at 11:05
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Its a common practice widely used in Electronics industry to denote period in electronics schematic diagrams. Most common reason is found to be the schematic diagrams are very complicated and usually these kind of notations like 3V3 or 1V8 will be denoted at power regulators or power rails and a period is very likely to be missed when is schematic is very complicated.

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  • \$\begingroup\$ I like 3V3 and 4R7 and 3C3. The letter tells us what unites we are talking about. Volts, Amps, resistance, capacitance, etc. \$\endgroup\$
    – user338146
    Commented Oct 5, 2023 at 13:23

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