20-30MHz Level-shifter 3.3V → 5V

Stefan Krueger

Other Parts Discussed in Thread: SN74LVC2G34, SN74HCT125, SN74LVC2T45, SN74LVC1T45, SN74LV1T34Hello TI community,

i often have the problem to interface 5V 'SPI-like' LED-Pixel-Strips with 3.3V controllers.
the stripes need Data and Clock signals in 5V levels and are good to about ~25MHz Clock Speed...
Often the first Pixel is >1meter away from the controller. I know that this is not a good starting point for this speeds -
but design-decisions are highest priority for art/exhibition things..

can anybody recommend a Logic / Level-shifter chip that is a good fit for this kind of usage?

i found the SN74LVC2G34 and think it could be a good fit..

Sunny Greetings
Stefan

over 5 years ago

0 Karan Kotadia over 5 years ago

TI__Genius 16725 points

Hello Stefan,

There are many complications in using >1 meter of transmission line. Please read the following FAQ to get a better understanding of transmission lines.

https://e2e.ti.com/support/logic/f/151/t/763609?tisearch=e2e-sitesearch&keymatch=faq%3Atrue

I cannot recommend you a part until I am clear on what method you are using to avoid reflections and other transmission line effects.

Thanks!

-Karan

0 Stefan Krueger over 5 years ago in reply to Karan Kotadia

Intellectual 670 points

Hello Karan,

thanks for the link to this great FAQ-entry.

for my needs - most of the time i just have wires - one for ground and one for Clock and one for Data..
not twisted.(and not always parallel)
so after reading the article i wounder that it is working at all ;-) (often i easily have up to 3meters cable length ;-)
but most of the time it is working ;-)
till now i use simple SN74HCT125 as level-shifters.
but these are only working up to about 6MHz.
and as this limits my actual 'animation refresh-rate' i started to search for other options..
in a blog-post i found the mentioning of the SN74HCT245N.
but its a little over-sized for most usages so i went on and found SN74LVC2G34 as a possible fit..

i know it would be better to use some fitting ways to transmit the data over such 'long' distances. easiest way could be to use a matching pair of LVDS chips and some CAT5e cable as twisted pair....
an LVDS391 and LVDT348 are on my desk and are waiting for some experiments for the next project ;-)

i hope i could give you some more background & framing for my needs.

sunny greetings
stefan

0 Karan Kotadia over 5 years ago in reply to Stefan Krueger

TI__Genius 16725 points

Hi Stefan,

I think the SN74LVC2G34 is a great choice. Operating it at 3.3V with a 5V power supply will cause some power consumption.
For translation, I would recommend the SN74LVC1T45 for single channel or the SN74LVC2T45 for 2 channels.

Thanks!
-Karan

0 ShreyasRao over 5 years ago

TI__Guru 58200 points

Stefan,

SN74LVC2G34 cannot work effectively as a 3.3 to 5V translator since the Vih of the device cannot guarantee a translation across PVT corners.

SN74LV1T34 or the SN74LVC1T45(or 2T) can work as a unidirectional 3.3 to 5V translation.

If there are 4 channels in the "SPI-like" interface, you could consider using 2 SN74LVC1T45 and one sn74LVC2T45.

0 Stefan Krueger over 5 years ago in reply to ShreyasRao

Intellectual 670 points

Thanks to you both Karan & Shreyas!!

i missed the point that the SN74LVC2G34 does not work as 3.3V to 5V translator in spec...
(Vih == 0.7 * VCC == 0.7*5.0V == 3.5V)
i will order some as 3.3V Status-LED-drivers ;-)

for my data & shifting needs i will go with the SN74LVC2T45!
the 'VCC Isolation Feature' is a great thing for my use-cases...!

sunny greetings
stefan

0 ShreyasRao over 5 years ago in reply to Stefan Krueger

TI__Guru 58200 points

Good to know, Thanks and good luck Stefan.

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20-30MHz Level-shifter 3.3V → 5V