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 23:46:14 +0000 Subject: Re: PI3USB14-A dual 4>1 USB switch for analog Newsgroups: sci.electronics.design References: <70go2jt7uje3qft4k788sqijrps9diidss@4ax.com> From: Phil Hobbs Message-ID: <0069906b-da42-fda4-46ce-4167d9584e8d@electrooptical.net> Date: Sat, 27 Apr 2024 19:46:13 -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: <70go2jt7uje3qft4k788sqijrps9diidss@4ax.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Lines: 104 X-Trace: sv3-YnFP7x3JfnG1U1Olb0Dt/gIHyf7F9lZpYQyrbxuz+/iW7XxJJUq1Nj9Q1lKPC1yRCrWMtBaN04KSvEJ!R1L5kMnocqmpeXGYJh/ALY2u1m75OcC4j61NuIZnZVz3lRR5XcbRKua1QZa0P7gpvbf92YAqdMMK!SJ5uM+1p5RUdSDcIktUj/dU= 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: 5561 On 2024-04-26 20:07, John Larkin wrote: > 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. > Since everybody gave up on having the part numbers fit on the package, the sky's the limit. 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