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I'm working on a schematic for an yet another Nixie IN-12 clock using a Raspberry Pi Zero 2 and HD5522 32-channel serial-to-parallel converter with open drain outputs to sink the Nixies.

The HD5522 Datasheet says its Vdd is -0.5 to +15V but recommends 10.8V to 13.2V. As the Raspberrys IOs are +3,3V I'd love to use 3,3V as Vdd.

I've seen other Nixie projects using a Vdd of +5V for the HD5522. Are there any limitations of using a Vdd of 3,3V?

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If the recommended range is 10.8V to 13.2, it means the recommendation is 12V with a tolerance of 10%.

It is likely that it won't work at 3.3V, and using it outside of recommended values is not recommended.

The -0.5 to 15V range are the absolute maximum values. It means that it will get damaged if these are exceeded. It does not mean it will work properly or at all within that range.

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  • \$\begingroup\$ how is it possible that in other Nixie projects they are used with an Vdd of +5V? If I use an Vdd of +12V - which I also have on the board - I'll should us a mosfet/bjt to for the SPI, latches... and +12V right, or am I missunderstanding something? \$\endgroup\$
    – BennX
    Commented Jan 30, 2022 at 19:50
  • \$\begingroup\$ If I see that correct an input high is min Vdd -2 which for me seems confusing. \$\endgroup\$
    – BennX
    Commented Jan 30, 2022 at 19:52
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    \$\begingroup\$ It is possible because these projects are likely one-off hobby projects made by hobbyists and they are using the parts outside of recommended specifications. It might work, or it might not, hobbyists may not know or care about it. If it does not work they might try another chip and it may work better. That's why some people say that you can use parts outside of specs as it has worked for them, once, but other people may not be able to get it working even if they tried 10 parts. Even if it works, is it reliable and how long it will work may also be good questions. \$\endgroup\$
    – Justme
    Commented Jan 30, 2022 at 19:57
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    \$\begingroup\$ Yes, CMOS data inputs need about 80% of VDD level to be reliably read as high logic level. This chip is no exception, if you have 12V supply, a 10V input on data pin is required to be within specs. \$\endgroup\$
    – Justme
    Commented Jan 30, 2022 at 20:00
  • \$\begingroup\$ Thank you very much for your help. Essentially I'd need to use the +12V on my board and add mosfets to amplify the MOSI and CLKs using the 3,3 of the raspberry. Any reading recommendation for how to do that properly? \$\endgroup\$
    – BennX
    Commented Jan 30, 2022 at 20:03

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