Not sure what forum is proper for my question, this one or generał electric. But decided to write here.
I have an issue with PCF8574A ic.
I've created simple port expand board. Mostly works fine, but found 2 issues.
Periodically have error from TwoWire lib - address send NACK. It looks like unavailability of the board for communication. Sometimes it can be even in the very first communication (pcf.begin() function).
And second, much more important issue. If it will be any noise on the Vdd wire - device fell into latach state. Current consumption is more than 200mA (probably up to USB capacity) , IC becames extremely hot...
This latach issue can be casud by just touching Vdd wire by screwdriver (even without touching metal part of screwdriver by hand!).
I've tested it with very simple circuits. Arduino nano, 20cm wires, pull-up resistors added to sda sck (10k).
I evet added tantal electrolitic capacitor and 2 100n ceramic just on the top of the IC.
Welcome! Yep sounds interesting but I cannot help without knowing what you have and how it is connected. Post an annotated schematic showing exactly how you have wired it, include all component parts such as resistors, capacitors, etc. Also show all ground connections, power sources and notate any leads over 10"/25cm in length. A clear picture of what you have would help. Posting your code will be a big plus.
Ооkay. Looks like i found what cause it. I've replace IC with another, bought different, and it works!
O the pic you can see both: good one on the right and bad one on the left (desoldered).
Yep, bad has "a" suffix, but the obly difference i found - address in i2c bus...
I will add schematic a little bit later if you are interested.
I agree that schematic and pcb can cause communications problem, right. But secon issue, this latach with huge current consumption and overheating, caused by just very tiny noise on the Vdd - this is IMO disqualification for IC. It was big surprise fore me, i made by TI, i didn't expect such behaviour. Do you see any possible issue with it in future for my design?
In your image, the faulty IC at the left has a small blob in the plastic on the top near pin 8. That can be due to overheating.
It's not so much about it being TI or not; it might have been the seller or manufacturer.
The IC might have been abused and been damaged before you even got it. Be aware that people buy stuff, abuse it and when it fails it's returned to the seller for a refund/replacement. The seller might happily put it back in stock and sell it again.
Not saying that this is the case but you might have made a wiring mistake which resulted in damage.
this issue (latch up, sorry, i didn't know how to call it properly) can be caused by just touching the Vdd wire be any metal item (in my case it was screwdriver, and I didn't touch metal rod of it). As I wrote - I even add tantal capacitor with 2 ceramic (100n) just on the top of the IC (soldered to the Vdd and Vcc legs) - and issue still present. With another IC issue has gone...
A lot depends on your electromagnetic environment. By touching a part with a screwdriver, you are in effect adding an antenna to that part. This then causes additional signals that can drive the part into a latch up state.
Well with an other IC the issue has not gone away, it has just reduced to where it is no longer critical. You can't say it has gone, just that it is below the level that causes an issue.
