Re: PI3USB14-A dual 4>1 USB switch for analog

On Thu, 25 Apr 2024 12:28:42 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

Hi, all,
>
I'm in a bit of a rush, doing revs to a testing board for a prototype
lidar ASIC that turns out to be..., um..., well....  Let's just say it's
a _tiny_bit_delicate_ electrically.  Yeah, just a little delicate,
that's it. (Not our design or our nickel, fortunately.)
>
It runs on a single supply, so the only sequencing issues are with the
signal pins. Thus the test board is going to bring up V_DD smoothly and
not too slowly: a monotonic edge of about 100 us.  While that's going
on, all the inputs and outputs will see 100k ohms to ground. (All the
enables are positive-true, which makes this easier.)
>
The digital pins are all inputs, so they're just buffered with
SN74LVC1G125s (tri-state Schmitt noninverting), with the aforementioned
100k to ground on their outputs.
>
The analog outputs don't have much drive, but can go pretty fast if you
keep the capacitance down.  There are a fair few of them, so I want to
mux them down before the op amp buffers (OPA2626es--surprisingly nice
chips).
>
Because we're not made of money, and the test boards aren't ITAR, we're
getting them made and stuffed at JLCPCB.  Thus we care a lot about what
their tame distributor LCSC has in stock.
>
They're fairly light on analog muxes, it turns out.  Going through what
they do have, I was reminded just how awful the capacitance of old-timey
mux parts is--way over 100 pF at the common pin of an 8-1, blech.
>
They do have these very nice-looking USB switches, type PI3USB14-A, for
pretty cheap ($0.45 @ 1ea) and in plentiful stock.
>
They look beautiful--6 ohms R_on, 4 pF C_off typical--but apart from one
crosstalk number, the datasheet gives only sketchy hints about their
actual analog performance--bandwidth and crosstalk, but nothing about
charge injection, switching times, make-before-break, resistance
linearity, or distortion.
>
Has any of you used them for actual analog stuff?
>
Thanks
>
Phil Hobbs

We use TS3USB30EDGSR to switch/mux fast signals. We mostly use them as
setup-time switches, things like polarity switching and low/50r source
impedances, things like that, so we haven't explored dynamics much.
They do propagate fast signals nicely.

How about using relays?