5V on 3V3 Altera CPLD I/O - Page 1
Forum section: electronics / general

author: pyroesp
author_rank: Regular Contributor
timestamp: September 02, 2013, 03:58:12 pm
content: So I have this idea where I have to use a CPLD to do some logic on a 5V board, but the CPLD (EPM240T100) is 3V3 only.I can't just change the 5V board into 3V3.So my question is: Can I connect 5V on a 3V3 I/O, without a level shifter ?My thought on this is you can, but I'll have to limit the current and power dissipated on those pins, right ?

author: RoadRunner
author_rank: Frequent Contributor
timestamp: September 02, 2013, 08:17:36 pm
content: i guess this may be helpfulhttp://ww1.microchip.com/downloads/en/DeviceDoc/chapter%208.pdf

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 02, 2013, 08:53:08 pm
content: Series resistor and clamp diode. According to the datasheet, some MAX II devices have internal clamp diodes

author: pyroesp
author_rank: Regular Contributor
timestamp: September 02, 2013, 09:06:40 pm
content: Oups, EPM240 is altera... not Lattice. Changed the title.Thanks for the pdf Gaurav and thanks for the help Mike.I have to find out if the EPM240 has clamping diodes.Cheers,pyroespEDIT:Doesn't seem like it has clamp diodes.Quote from: MAX II Device HandbookWhich is strange because if you look at the image below, I can't see any clamp diodes, just a couple of 100 ohm resistors to limit the current.

author: marshallh
author_rank: Unknown
timestamp: September 02, 2013, 10:52:06 pm
content: He's cheating on that pcb... not surprising.Buy a few proper octal level converters, problem solved.

author: pyroesp
author_rank: Regular Contributor
timestamp: September 03, 2013, 02:56:33 am
content: Goddamn lead free components...I've looked a bit on digikey and found the SN74LVCC3245ADWR (1.26$) and EPM240T100C5N (6$).Hopefully, soldering with non lead free solder won't do anything bad.

author: hlavac
author_rank: Frequent Contributor
timestamp: September 03, 2013, 03:01:37 am
content: If what this plugs into is using 5V TTL logic you may get away with using 3,3V CMOS with series resistors on the inputs.ESD protection diodes will clamp the TTL inputs which are weak TTL pullups and together with the series resistors the current from logic high into the protection diode will be limited.For outputs, TTL logic threshold for high is only 2V so you are fine with 3,3V high from CMOS.Only problem will be that the 3,3V rail will have current dumped into it from 5V through all these pullups to 5V, you need a regulator that can survive this and not allow the 3,3V to go higher than 3,3V.

author: c4757p
author_rank: Super Contributor
timestamp: September 03, 2013, 03:17:41 am
content: Quote from: pyroesp on September 03, 2013, 02:56:33 amHuh?

author: pyroesp
author_rank: Regular Contributor
timestamp: September 03, 2013, 07:25:52 am
content: @hlavac: I think I'm going to use the level shifters, just to be sure.@c4757p: Sorry, I must have phrased that incorrectly.What I'm trying to say is that I don't have any lead free solder and I am hoping that I can use tin-lead solder.Though it will be a while before I have a board to solder components on so I might buy some lead free solder in the meantime.

author: FrankBuss
author_rank: Unknown
timestamp: September 03, 2013, 08:01:40 am
content: Quote from: pyroesp on September 03, 2013, 02:56:33 amI've used the SN74LVC8T245 in one of my last projects, works fine. Same price, but compared to the SN74LVCC3245, it doesn't matter on which port is the 3.3V level and it works down to 1.65V instead of 2.3V (but not important for 3.3V/5V level translation).If you need more than 8, take a look at the 16 bit (dual 8 bit) level converter SN74ALVC164245. Cheaper than two 8 bit chips and needs less board space.QuoteWorks fine, I solder with leaded solder all the time for my hobby projects (unfortunately can't do this for customer projects). The usual copper wire is just copper, too, and you can solder it just fine

author: pyroesp
author_rank: Regular Contributor
timestamp: September 03, 2013, 03:40:24 pm
content: Quote from: FrankBuss on September 03, 2013, 08:01:40 amI'm going to check that one. I've never done SMD soldering at home, so I hope it's not too small ^^.Quote from: FrankBuss on September 03, 2013, 08:01:40 amAwesome!

author: Unknown
author_rank: Unknown
timestamp: September 03, 2013, 03:55:34 pm
content: Quote from: pyroesp on September 03, 2013, 02:56:33 amWhere have you been buying non-lead-free parts the last ~6 years? Almost all components have been lead free for years.

author: pyroesp
author_rank: Regular Contributor
timestamp: September 03, 2013, 04:25:50 pm
content: Like you said, almost all...I haven't bought/built anything special in a while and If I do, I can find some/most of the components at home.The university was going to throw away like 4 boxes of resistors/inductors and 40XX/74XX ICs.And I get free microcontrollers from microchip every once in a while.The last thing I built was a ball-in-a-maze puzzle with accelerometer and GLCD for a universyti project. The only thing I bought was the PCB and the accelerometer. Everything else got recycled from other electronic devices.