Help with CPU to Level-Shifting Transceiver

Hi guys,

I am working on a project where i need an ESP8266 to communite through a 16-Bit 2.5-V to 3.3-V or 3.3-V to 5-V Level-Shifting Transceiver With 3-State Outputs. I have picked up a SN74ALVC164245 ( which I expect should be able to do just that.

To start off, I want to confirm i can reliably send data in to one side of the chip, and read it on the other side of the chip. Unfortunately, I’m having trouble with that. My high’s look fine, but my low’s oscillate like crazy… It could very well be a complete newbie issue (as I am one) so perhaps you guys can spot what I’m doing wrong.

I hook up my ESP to side A (3.3v side), with:

  • A1 connected to GPIO2
  • OE connected to GPIO4
  • DIR connected to GPIO5

I supply 3v3 to the ESP and to the A side of the chip. I supply 5v to the B side of the chip. I connect GND for the powersupplies, ESP and the chip.

My ESP runs code that sets OE to low and DIR to high (A data to B bus operation), and then pulls GPIO2 low for 1 sec, high for 1 sec, low for 1 sec etc…

When I read B1, i see the attached result - Highs look OK, but when i pull GPIO2 low, i get oscillation on B1.

Any advice would be greatly appreciated!

I see no decoupling capacitors... That high speed high current logic chip without decoupling
could do all sorts of mayhem. 10nF directly on each of the 4 supply pins to the ground plane (you
need a groundplane with this sort of chip really). Add 1uF on each rail fairly close to the chip,
all ceramic surface mount capacitors.

You also seem to have many unconnected inputs, which is a bad thing, they will easily oscillate
and or draw shoot-through currents.

Can you show the PCB layout you're using?

Thanks Mark!!

I don't have stuff on a PCB yet. I have the chip soldered to a TSSOP til DIP board, and then wire everything else up..

I do have a lot of unconnected pins, but the documentation points out that i should connect inputs, so I have done that for the segment of the chip i use. But understood, i should connect them all.

Apologies for being a newbie, but forb"the 4 supply pins", you mean the two 3v3 and the two 5v on the chip, correct?

The 1uF for each rail - Do you mean one for each input and one for each output? (32 in total).

Would it be quick for you to link me those components above, so Im sure i know what to look for?

Thanks in advance!

Rail as in supply rail - the four pins you’ve identified. You never put decoupling capacitors on signals,
they go from each supply to ground. All logic chips need decoupling, its never optional.