I have been trying to make a 3.3V circuit controlled by an Arduino (5V logic.)

I have used a logic converter circuit similar to the SparkFun/Adafruit ones. My problem is that whenever i try to increase the clock speed of the main circuit up to 1MHz, the circuit does not work.

What options are there for high speed logic conversion? I don't necessarily need bidirectional conversion, however it would be nice if it would be bidirectional.

  • 2
    \$\begingroup\$ Logic level conversion for which bus? And for which speeds? Usally you would use a logic buffer that tolerates 5V input signals when it operates on 3.3V supplies. \$\endgroup\$
    – Justme
    Jul 7, 2020 at 0:45
  • 1
    \$\begingroup\$ Parallel connection between what devices? How many parallel wires? How long would this connection be, and with what kind of wires would this 2 MHz signal pass? \$\endgroup\$
    – Justme
    Jul 7, 2020 at 0:55
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    \$\begingroup\$ "similar to ..." isn't a circuit. Can you provide the schematics for what is not working at higher speeds but works at lower? \$\endgroup\$
    – jonk
    Jul 7, 2020 at 0:57
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    \$\begingroup\$ It sounds like you're trying to use a bidirectional logic shifter when a unidirectional one would do the job. It's a lot easier to make a unidirectional shifter fast. \$\endgroup\$
    – Dave Tweed
    Jul 7, 2020 at 1:21
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    \$\begingroup\$ Please post a schematic of the circuit that is not working for you, or a link to the Sparkfun circuit, or something ... \$\endgroup\$
    – AnalogKid
    Jul 7, 2020 at 2:50

1 Answer 1


There are bidirectional level shifters designed for I2C, that have internal speed-up logic to improve the risetime. These can certainly do a couple of MHz no problem.

Maxim appnote: https://www.maximintegrated.com/en/design/technical-documents/app-notes/1/1159.html

There is also the pass-transistor type, but you need to add strong-enough pull-ups to get the risetime when translating up. Translating down is no problem.

Example: https://www.ti.com/product/LSF0204D


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