Path: ...!Xl.tags.giganews.com!local-1.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Sat, 27 Apr 2024 00:09:02 +0000 From: John Larkin Newsgroups: sci.electronics.design Subject: Re: PI3USB14-A dual 4>1 USB switch for analog Date: Fri, 26 Apr 2024 17:07:10 -0700 Organization: Highland Tech Reply-To: xx@yy.com Message-ID: <70go2jt7uje3qft4k788sqijrps9diidss@4ax.com> References: X-Newsreader: Forte Agent 3.1/32.783 MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Lines: 86 X-Trace: sv3-S7J64W1hOpm3pFZtj+aH3qu/KTtHelFaE0Z5v+IWtSe9ekcHjAy6Hm+Q6LqgRqGRXO2opCIDg2oBWn1!2iIEsJv6cTujr0nUn5ihw+UnEnsTdZ0CskQvM3VZD6D9CEDe/i0z5Cute58qnC/gi7NpZeo5uhox!A85MHw== 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: 4912 On Fri, 26 Apr 2024 19:30:58 -0400, Phil Hobbs wrote: >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 My MAX record shows OnSemi NLASB3157DFT2G as an acceptable sub. They hires sadists to make up part numbers. I like HH Smith, with part numbers like 101.