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From: Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>
Subject: PI3USB14-A dual 4>1 USB switch for analog
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Date: Thu, 25 Apr 2024 12:28:42 -0400
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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

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com