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I have built a PCB using IC 74HC245D for levelshifting 3.3v signal to 5v signal for RGB LEDs. But by mistake, I used TSSOP-20 footprint in my PCB, and while ordering parts I ordered a SOIC package so it's a mess as TSSOP IC is not easily available in India.

After a lot of searching, I got one IC that might work but I am confused that it will work with 5v or not. IC is 74LCX245MTCX datasheet says that it can tolerate up to 7V. The link for the datasheet is Here.

enter image description here

But when I looked more into the datasheet I found it says the max is 3.6V so now I am confused, will it work with 5v or not?

enter image description here

Attaching my current schematic I am using 5v as Vcc. enter image description here

Anyone here might have used this IC and can share some more info or any alter part that I can use.

Thank you for the help.

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    \$\begingroup\$ The 74LCX245MTCX is 5V tolerant, but it can't actively drive a 5V output. (Since it's not rated for Vcc = 5V.) \$\endgroup\$
    – Velvet
    Commented Sep 5, 2023 at 6:25
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    \$\begingroup\$ These are very easy to find 2nd source for since it's a standard IC. Different manufacturers might use different combinations of gibberish letters, 74LVC245, SN74LVC245 etc. This is because part numbers weren't decided by rational people back in the days. I very much doubt that you can't buy any part by any of the major silicon vendors. Far more likely, your purchase channels are bad. \$\endgroup\$
    – Lundin
    Commented Sep 5, 2023 at 6:32
  • \$\begingroup\$ Actually the HC type you were originally using would have been a mistake anyway. HC can't be used to level shift 3.3V inputs to 5V outputs. \$\endgroup\$
    – Justme
    Commented Sep 5, 2023 at 6:58
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    \$\begingroup\$ "HC is not suited on paper" There you go. Please design with something which is suitable for your own sake. Using components out of spec is one of the most robust ways to have production problems and customer returns. \$\endgroup\$
    – winny
    Commented Sep 5, 2023 at 9:20
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    \$\begingroup\$ @winny I agree with your design advice. I also agree with the OP's note "They have done intense testing to find it and use it on a daily basis" in situations such as described. If the supplier is prepared to warrant the part in such use then they have effectively produced a relevant datasheet. ... \$\endgroup\$
    – Russell McMahon ♦
    Commented Sep 5, 2023 at 12:05

3 Answers 3

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Staying inside the absolute maximum ratings guarantees that the device will not be damaged.
Staying inside the recommended operating conditions guarantees that the device will work correctly.

Neither the 74HC245 nor the 74LCX245 are guaranteed to be able to do the level shifting you want; the minimum VIH specification is above 3.3 V for a 5 V supply (and the 74LCX245 does not even specifiy it for 5 V).

To be able to input 3.3 V and output 5 V, you need a device with TTL-compatible inputs, e.g., from the HCT or AHCT logic families. So look for chips named (SN/CD)74HCT245, (SN)74AHCT245, or SN74LV8T245. You could also use unidirectional buffers with a similar footprint like (SN)74HCT541 or (SN)74AHCT541 if you pull pin 1 low.

Please note that unused inputs must never be left floating. Connect the A1/A3/A5/A7 pins to VCC or GND or a neighbouring input. (You could also use two channels in parallel for each LED to increase drive strength.)

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  • \$\begingroup\$ Yes I read the datasheet and got that info, not to leave floating pins will be fixing that in V2. for now I can short them with solder to fix it not a big challenge on that. \$\endgroup\$
    – Dharmik
    Commented Sep 5, 2023 at 8:02
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Over 30 000 devices in stock at Digikey. They ship all over the world, including India. Just place an order for the TSSOP-20 part and it will arrive.

https://www.digikey.com/en/products/filter/buffers-drivers-receivers-transceivers/704?s=N4IgjCBcpgbFoDGUBmBDANgZwKYBoQB7KAbXABYBmAdgFZqQBdAgBwBcoQBlNgJwEsAdgHMQAXwLkI0EMkjps%2BIqRAAmAAyraATgbMQ7TjwEjxBVeQYy5C3AWKQyU2rQAc6pqw6RufIaIkQWksEWVRMO2VHNVcwKQ99Qx9jfzNwbVdtUJsIpQcyBMCAWnJs8MV7FTAwQoIi1TLIPgBXPJVaJmKs6ygWtuiIRjFhoA

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    \$\begingroup\$ Have already checked a few reasons not for ordering, will take more time to reach, high shipping and import duties. \$\endgroup\$
    – Dharmik
    Commented Sep 5, 2023 at 9:37
  • \$\begingroup\$ @Dharmik Respin the board and use 5 V tolerant parts. \$\endgroup\$
    – winny
    Commented Sep 5, 2023 at 9:48
  • \$\begingroup\$ I'm afraid you keep trying to adjust the facts to fit your views, rather than the other way around. You seem to keep rewriting the question to one you wish it was. The OP made it clear from the start the problems they face with shipping. If it was that easy, they'd have done it already. Downvoting for that reason. \$\endgroup\$
    – TonyM
    Commented Sep 9, 2023 at 19:23
  • \$\begingroup\$ @TonyM What fact did I adjust? Do you mean Digikey does not ship to India? \$\endgroup\$
    – winny
    Commented Sep 9, 2023 at 20:34
  • \$\begingroup\$ It's all there already for you to read... (That's if you're accepting that the OP knows their situation considerably better from being in it, than you do knowing the bare minimum from a long way away.) \$\endgroup\$
    – TonyM
    Commented Sep 9, 2023 at 20:56
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I just wanted to extend my heartfelt thanks for all your fantastic suggestions and support.

After a lot of contemplation, I took a leap of faith and decided to give the 74LCX245MTCX IC a shot to see how it would mesh with my PCB design. I placed an order for the IC, soldered it onto one of my PCBs, and to my delight, it worked like a charm!

I'm excited to share that all the animations on my 1-meter LED strip, which has 96 LEDs per meter, are running incredibly smoothly. I plan to further put it to the test with a longer strip, and I'll be sure to keep you all posted.

enter image description here

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    \$\begingroup\$ OK, but you did not listen to the suggestions, or decided to ignore them. It is the wrong chip for 3.3V to 5V logic level conversion. It is not rated for 5V usage, only up to 3.6V, and manufacturer does not recommend exceeding the recommended operating conditions. It may work now, but it does not have to work at all, it may damage and even if this chip works it does not mean all other chips you buy will work. \$\endgroup\$
    – Justme
    Commented Sep 9, 2023 at 15:28
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    \$\begingroup\$ "I'll be sure to keep you all posted", "Stay tuned for more updates" There can't be more updates, Dharmik. It's a Q&A site, not a discussion forum or your blog. As it's a Q&A site, this cannot be the answer to the question if it's not definitive and provable. Instead, you describe an experiment and another user (@Justme) has rightly pointed out that this is bad engineering: using a component outside its rated specifications. I understand you have supply problems but accepting this answer yourself doesn't make this a solution that others can reliably refer to. \$\endgroup\$
    – TonyM
    Commented Sep 10, 2023 at 19:28
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    \$\begingroup\$ Dharmik - Hi, The site allows self-answers to be "áccepted" by the OP (i.e. you). If there are problems with that answer, you may see downvotes or comments explaining them. Although people are allowed to edit an answer (even a self-answer) to improve it, this site is not a blog and shouldn't be treated like one. || If you are not sure that this is the correct solution to your question, then perhaps you posted this as an answer a bit prematurely? Or, if you are sure, then there is no need for updates. || If you have improvements to your answer (not blog-like updates) you can edit it. \$\endgroup\$
    – SamGibson ♦
    Commented Sep 10, 2023 at 19:54
  • \$\begingroup\$ The IC that I used is rated up to 7V yes I do accept that it can perform optimally under 3.6V but I wanted to test what happens if I use it for 5V and whether this IC can provide sufficient conversion speed for the WS2812b LED strip. And one more thing I did not test only 1 IC, I tested 10IC with different circuits and all worked perfectly fine with WS2812b It was installed successfully in my House and working fine. So I believe the datasheet it can stand up to 7V and if can reduce performance after 3.6v but its more than enough needed for WS2812b. \$\endgroup\$
    – Dharmik
    Commented Oct 7, 2023 at 7:29

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