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