Path: ...!Xl.tags.giganews.com!local-1.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Fri, 26 Apr 2024 23:30:59 +0000 Subject: Re: PI3USB14-A dual 4>1 USB switch for analog Newsgroups: sci.electronics.design References: From: Phil Hobbs Message-ID: Date: Fri, 26 Apr 2024 19:30:58 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Lines: 88 X-Trace: sv3-37j2vRRmCfsKo+gcacAINR1k3L9sW3/utNtdTaKC5MQc9pDjC3+4xyi6KF74W2b8HvF/IiBS51nXvV6!Ca6NI9n62wsNGd2BaC7KwlBy3kavK0Lpf3v0gsM742B/vlL+V3P1GPLb1N4ajqmQRu/ZpAj8K7lL!Rmqbx+gsVn3kOPAhMznL8oiz X-Complaints-To: www.supernews.com/docs/abuse.html X-DMCA-Complaints-To: www.supernews.com/docs/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Bytes: 4860 On 2024-04-26 14:03, John Larkin wrote: > On Sat, 27 Apr 2024 01:12:13 +1000, Chris Jones > wrote: > >> On 27/04/2024 1:01 am, Chris Jones wrote: >>> On 26/04/2024 2:28 am, Phil Hobbs 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 >>>> >>> >>> As long as you don't need the signals to swing near the positive rail, I >>> suggest you google "H-mode mixer" as a lot of amateur radio enthusiasts >>> have built mixers using bus switches, basically just nmos fets with a >>> gate driver. For example: >>> https://martein.home.xs4all.nl/pa3ake/hmode/switches.html >>> >>> They may not be better than the PI3USB14-A but I have a better guess of >>> what is in them. >> >> Ah, I see they also tried ones with both NMOS and PMOS devices in the >> switches. The FSA3157 seems to have somewhat more complete >> specifications than the one you mentioned. > > > > The 3157 is nice too, SPDT in a small package, with specified charge > injection. We pay 7 cents. The onsemi FSA3157 is obsolete, unfortunately. There are TI and Diodes Inc versions that you can still get, Cheers 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