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I have a range of data signals and clock signals that I want to translate down from approximately 5 V to the 3.3 V range. Is there an IC available to perform this task?

The various signal frequencies are 60 Hz, 3.5 MHz, 238.6 kHz.

Data Signal

Sync Signal

The required need for voltage translation/shifting is because, if I am reading this correctly, the target FPGA (ICE40LP8K) will not tolerate anything above 3.6 V:

FGPA Specifications

FPGA Recommended

Source: iCE40 LP/HX Family

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  • \$\begingroup\$ Are the signals bidirectional? Like I2C for example? Or can there only be one driver of the signal lines? \$\endgroup\$
    – jusaca
    Sep 20, 2023 at 16:34
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    \$\begingroup\$ Yes. There are many such parts. Look for "level translator" on Digikey.com. Depending on the speed of your signal, you may be able to get away with a resistor divider. Do you have any signals going the other way (3.3V TO 5V)? Usually, with digital signals, no translation is required in this direction. \$\endgroup\$
    – Troutdog
    Sep 20, 2023 at 16:37
  • \$\begingroup\$ The signals are incoming only \$\endgroup\$
    – Rob Holmes
    Sep 20, 2023 at 16:37
  • \$\begingroup\$ @RobHolmes Countless products have been around for 20 or maybe even 30 years, now. Surprised you haven't found them. Look up voltage translators and level shifters. TI is heavy in this area, for example. There are also single BJT or FET arrangements that can be made to work here, as well. Discrete or IC, your choice. Also look here on this site. \$\endgroup\$ Sep 20, 2023 at 16:44
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    \$\begingroup\$ You don't even need a level translator (as such) for this. A 3.3 V buffer with 5-V tolerant inputs will also work fine. \$\endgroup\$
    – The Photon
    Sep 20, 2023 at 17:19

3 Answers 3

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Any standard logic IC such as a buffer that can tolerate 5V on input while being powered with 3.3V to provide 3.3V output will do.

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    \$\begingroup\$ Yup, 74LVC series is usually the go-to. \$\endgroup\$ Sep 20, 2023 at 18:02
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There are specialized ICs, usually going by term "Level shifter" or "voltage translator". Level shifters can be used for fast signals (low delay, fast rise time) and can be uni- or bidrectional.

Many level shifters allow enabling and disabling either side of the device, to avoid sending signals to a part of the circuit that may be powered off. The circuits can also be used to enhance the drive capability or offer better isolation and transient protection in comparison to the original device.

If the signal is of a communication bus, you might find a more suitable device by the name of repeater or signal buffer, many of such devices do not offer level shifting, but some do.

If the signal being switched is a slow, general purpose IO, you can use a resistor divider for one way level shifting or for two-way shifting a FET circuit (for slow signals), such as in this:

FET Circuit

Image source and tutorial: https://learn.sparkfun.com/tutorials/bi-directional-logic-level-converter-hookup-guide/all

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    \$\begingroup\$ Note that not any ol' MOSFET will work here. A keen eye will see that for Q1 to be appreciably "on", its \$V_{GS(th)}\$ rating will have to be quite a bit less than the LV voltage. A 'FET with 3.5Vgs(th) for instance, will never turn "on" at all at 3.3V, so its drain will always be at HV. \$\endgroup\$
    – rdtsc
    Sep 20, 2023 at 17:13
  • \$\begingroup\$ Such a bidirectional FET will not work for high frequency signals. And bidirectionality is not needed here. No specialized level shifter is needed either, any standard logic IC that can tolerate 5V on input while being powered with 3.3V will do. \$\endgroup\$
    – Justme
    Sep 20, 2023 at 17:41
  • \$\begingroup\$ Clarified that also the FET circuit is for slow signals. Looks like the question has been updated with some signals. \$\endgroup\$
    – Ralph
    Sep 20, 2023 at 17:47
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If you only need 5 V to 3.3 V translation, and not the reverse, and you only need it to work at low-ish (less than a few hundred kHz) speeds, there's a very simple circuit that will do this: a voltage divider. Even better, you can just use a simple 1:2 resistance ratio for it!

I'd put a circuit diagram here, but for some reason circuitlab isn't cooperating.

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    \$\begingroup\$ That depends on the requirements. A level shifter made of resistors for 230 kHz or 3.5 MHz with low enough power consumption while providing high enough bandwidth are not practical. A single quad buffer chip would convert all mentioned signals without any hassle. \$\endgroup\$
    – Justme
    Sep 22, 2023 at 20:06
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    \$\begingroup\$ @Justme Fair point. I've used voltage dividers for level shifting in the past, but only at low speeds. You could compensate one for high-speed operation by using some capacitors as well, but at that point a buffer chip would, as you say, be the better option. I've modified the answer to mention this limitation. \$\endgroup\$
    – Hearth
    Sep 23, 2023 at 3:53

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