Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: Phil Hobbs Newsgroups: sci.electronics.design Subject: Re: Curve Tracer Date: Fri, 7 Feb 2025 14:18:48 -0000 (UTC) Organization: A noiseless patient Spider Lines: 81 Message-ID: References: <37m4qj9v64kq4i20atrm4a5f59rpgd0n12@4ax.com> <9s65qj9o6felc0prbf30rlbmt7sm1lkb9q@4ax.com> <3u85qjd1t14atacquac79cb90buh1erfim@4ax.com> <6n37qj97tr4frn6skqs79jh7hjrs4fnavr@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Fri, 07 Feb 2025 15:18:49 +0100 (CET) Injection-Info: dont-email.me; posting-host="8cc3b19f144f730329d724108daaf523"; logging-data="3718831"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19xxHl/afmUTEFztVU1m5E/" User-Agent: NewsTap/5.5 (iPhone/iPod Touch) Cancel-Lock: sha1:dvLakFc3yYIFj0jCcLE8Nd/OeSw= sha1:J93boz5/IfRethWXnP99/rg17Gg= Bytes: 4865 piglet wrote: > Bill Sloman wrote: >> On 7/02/2025 8:18 am, john larkin wrote: >>> On Thu, 6 Feb 2025 23:11:58 +1100, Chris Jones >>> wrote: >>> >>>> On 6/02/2025 2:45 pm, Bill Sloman wrote: >>>>> On-Semi makes two monolithic duals, the NST45010 and the NST45011 >>>>> >>>>> https://www.onsemi.com/pdf/datasheet/nst45010mw6-d.pdf >>>>> https://www.onsemi.com/download/data-sheet/pdf/nst45011mw6-d.pdf >>>>> >>>> >>>> What makes you think those are monolithic? I think they are separate >>>> chips, but measured to have similar parameters, like the BCM846BS. >>>> >>>> The thermal coupling between the chips will be poor, so they will no >>>> longer be matched if the dissipation is not the same between them. You >>>> could cascode a current mirror to fix that, but if you are trying to >>>> make an exponentiator (as used in analogue synth VCOs) then you are >>>> stuffed, because you need to operate the two transistors at different >>>> currents, that being the whole point of the circuit. >>>> >>>> You will know if they are monolithic because it will have a pin called >>>> "substrate" or a note saying one of the pins is the substrate, and there >>>> will be a spec pointing out that the voltage between the two devices >>>> must be kept below some lowish value. >> >> You would know if they were monolithic if they did have a substrate pin. >> >> The fact that they haven't got one isn't proof that they aren't >> monolithic. A stronger argument is that they haven't put any limits on >> device-to-device voltages. >> >> My reason for thinking that they were monolithic was the 2mV worst case >> and the 1mVB typical difference in Vbe at 2mA. >> >> Monolithic does seem to offer the cheapest route to get that. >> >>> They are two similar chips, not monolithic. Thermals will be awful. >> >> Prove it. >> >> They may be two separate close-to-identical chips. There isn't room in >> the package to mount them far apart, and the chip to chip thermal >> resistance can't be large, and has to be much smaller than the package >> to ambient thermal resistance, which is 328C/Watt. >> >> Thermals won't be awful. Somebody who doesn't know about Wilson current >> mirrors isn't going to be a particularly reliable source of information >> about that kind of subject. >> >> Interdigitated monolithic is hard to beat for thermal matching but >> side-by-side devices on the same subtrate aren't going to be any better >> than devices on separate substrates if the substrates are mounted >> back-to-back. >> >> -- >> Bill Sloman, Sydney >> >> > > I seem to remember someone here has an xray machine which could answer the > question? > It’s a FAQ that we’ve gone through many times, including my doing a bit of math on the datasheet for the BCV61 current mirror that used its thermal runaway spec to estimate the die-to-die thermal resistance. Turns out to be about the same as the die-to-ambient, 300-500 K/W. They really aren’t monolithic. Cheers Phil Hobbs There -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics