Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: Bill Sloman Newsgroups: sci.electronics.design Subject: Re: Curve Tracer Date: Sat, 8 Feb 2025 02:39:09 +1100 Organization: A noiseless patient Spider Lines: 76 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; format=flowed Content-Transfer-Encoding: 8bit Injection-Date: Fri, 07 Feb 2025 16:39:23 +0100 (CET) Injection-Info: dont-email.me; posting-host="1fdcbc7f3c283c3a1d759744859576a3"; logging-data="3745683"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+VPxJ1mg4MgjtGd9hTjBL6cyjV3RhgKFs=" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:AJj/MM+K75CuEt0v3ZMVQkZsOYE= Content-Language: en-US X-Antivirus-Status: Clean X-Antivirus: Norton (VPS 250207-0, 7/2/2025), Outbound message In-Reply-To: Bytes: 5036 On 8/02/2025 1:18 am, Phil Hobbs wrote: > 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. >> >> 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. Thermal runaway is all about die-to-ambient. How does it tell you anything about 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. That doesn't necessarily follow. -- Bill Sloman, Sydney