Electronic – Found a particular chip, now I can’t find it again

decoderi2c

A couple of weeks ago, I stumbled on a particular chip. At the time I didn't need it, but now I do and I can't find it again.

The chip was a 4-16 line demultiplexer, but its input came from an I2C interface, not from 4 input pins. You send it a 4-bit address, followed by a 1-bit setting, and it sets that pin to the value specified, without changing any other pin. For example, if you sent 3, 1 it would set pin 3 high. If you then follow that with, say, 7,0 the chip would set pin 7 to low, but leave pin 3 alone.

Other details about this chip that I remember is that it has a QSOP package, and I believe it uses a 3.5v supply. Neither of these are critical specifications for me, those are just details about this particular chip that I remember.

I've tried searching DigiKey, and replicating my previous Google search, but to no avail. Can anyone give any hints on how to find this chip? Or if you recognize the chip, could you please let me know its part number?

Much appreciated!

EDITED TO ADD:
It isn't an I/O expander. This chip is an i2c peripheral device, with its own i2c address block (0x20 if I recall correctly, and yes I've searched for chips with that address block 🙂 ).

It is somewhat similar to a 74×154 decoder/demultiplexer, in that it has 16 distinct output pins (see 74×154 datasheet). The major differences between it and the 74×154 is that the chip I'm looking for has an i2c input interface (instead of 4 dedicated input address pins, enable pins, etc.); each output pin can individually be high or low (the 74×154 can have at most one output pin low at any given time; all others must be high); and changing the value of one output pin does not affect the other output pins.

I want to use a couple of these with an Arduino, to control somewhere around 25 distinct outputs. I'd rather use 2 Arduino pins for i2c interface, than 25 dedicated output pins.

EDIT 2:
On closer examination of I/O expanders, I realized I misunderstood what an I/O expander is. It does sound like an I/O expander, so I'll check those out.

Best Answer

I agree with the others that it's an I/O expander with I2C (or 'two-wire') input.

If you do a parametric search on Digikey for SMT I2C I/O expanders with exactly 16 outputs you'll get more than 100, counting SMT package variations.

The cheapest one is the NXP PCAL6416AHF,128. It also happens to be the one with the largest quantity they currently have in-stock. I have a slight preference for NXP when it comes to I2C anyway, as they invented it.