Two versions of Multiplexer chip TCA6408A at LCSC

I have just ordered the parts to build the ESP32 controller and found that the MUX chip TCA6408AQPWRQ1, as per the BOM, is out of stock at LCSC.
They do have a few thousand TCA6408AQPWR ( no Q1 ).
On checking for differences in the data sheets I find that the TCA6408AQPWRQ1 has a voltage translation range of 1.8v to 3.3v. The TCA6408AQPWR range is 1.8v to 5v.
So I suspect the TCA6408AQPWRQ1 specified is out of spec switching the 5 volt relays.

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To me it looks like the operating voltage of the one without Q1 has a wider supply voltage spec. If you look at the circuit diagram you can see that the supply of the chip is connected to 3v3 so i2c will work on 3v3 no mater you use Q1 or not so no problem on that side. VCCP is connected to 5v this is the supply for the paralel output ports. They work on 5v 's actually the design say to use the version with Q1 and that is wrong as the Q1 version is rated to Max 3v3 for VCCP. So in my opinion the NON Q1 is the correct to use. I think @stuart has to look in to this as he might have chosen the wrong device.

Hi @alanaland and @Albert

I agree, I think the correct one is the “TCA6408APWR” part number C206177 from LCSC. Looks like confusion crept in with the automotive grade version.

I shall update the design and re-release. The existing chips do appear to work though, but I shall recommend people swap out.

@atanisoft one to be aware of!

Raised issue New controller uses TCA6408AQPWRQ1 which is not suitable for 5V operation · Issue #78 · stuartpittaway/diyBMSv4 · GitHub

I concur this looks like the correct part. Another option that should work would be the TCA6416A which uses split voltage (3v3 on I2C IO and 5V on GPIO as example). Note that TCA6416A is a 16 IO pin expander compared to the TCA6408 which offers 8 IO pins, slightly larger package so not a drop in replacement.

I haven’t seen any issues either but can order a few in my next batch order. Is it a direct swap?

For people on the hunt for the correct part. It is a bit hard to get not on aliexpress so if you want to replace the part:
Search ebay for item 254604247955
Farnell, Mouser and Digi-Key have them all at about the same price. Be aware of minimum order values at some suppliers

Just when I came home I checked, the IC with Q1 (on the package printed 6408AQ) it is getting warmer than the other parts while doing nothing. So not good. I looked for a temporary solution and there might be one. For the relays it is no problem to be switched with 3v3 the SSRelays I can’t judge. As the IO ports are not used yet I think it is safe to lift pin 16 up from the PCB and wire it to pin 1. That way the IO ports are going to operate on 3v3 within specs for the max voltage on pin 16 (VCCP).

@stuart do you have the ability to check if the SSRelays are still working when we use this solution?.

I have received boards with the 6408AQ chip, and I’m uncertain of how bad that is:
Will it blow up, or just maybe stop working?
Should I order the C206177 IC and replace? Without a hot air gun, it won’t be pretty…
Anyone tried the pin 16 hack Albert suggests?

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@Mads_Skov It will not blow up on you, it might stop working. If it does and you have any critical stuff connected to the relays it might go wrong. as these stop switching with a broken 6408QA. To be most safe just order the on that can handle 5V on VCCP. Replacing them is not to difficult as the old one doesn’t have to come from the board in one piece you can use a knife to cut it’s pins, after that you can clean the pc and place the new chip with a small soldering iron. If by accident you make shorts in between pins use a piece of solder wick to remove it.

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Excellent advice, Albert. Thanks.
I had thought about cutting the pins on the chip. I’ll do just that then. My TS100 with a fine tip will get the new chip in place. Until I get the new chip, I’ll test the board with the old then.

I just received my PCB’S.

@stuart , can you inform me if I have the “wrong” chip?

6408AQ I can read, aka understand it’s the correct type of chip.
The rest is unknown for me.

Code in the Chip:

Even if I have the “wrong one”, if I understand correctly there is a fair chance it will work without issues, yes?

AQ is wrong chip. see page 35 of datasheet

So I am about to finally make an order from JLCPCB since most items are in stock or have easy substitutions. JLCPCB is however still out of TCA6408APWR. I found some potential substitutes of which the PCA9557PW118(#2 in my part list) seams like the best fit. Is anyone able to confirm if any of these IC chips will work? Otherwise I might just order it and swap out for the correct part once I find a source in stock.


I am also missing the TJA1057GT/3J but based on reading elsewhere I will just leave that out for now.

Only other question I have is if anything is different &/or which one is newer for the GitHub versions. master or v4.3?

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Watching… I also have an issue getting the TCA6408APWR, I ordered my boards without most of the IC’s and have just been soldering them on as I can get them…

If PCA9557PW118 is a good sub then great…