langwadt@fonz.dk wrote:> On 23 Okt., 22:42, Joerg <inva...@invalid.invalid> wrote: >> langw...@fonz.dk wrote: >>> On Oct 23, 1:28 pm, Allan Herriman <allanherri...@hotmail.com> wrote: >>>> On Mon, 22 Oct 2012 14:22:49 -0700, Joerg wrote: >>>>> Folks, >>>>> Looked at Digikey and some others. Where are those huge capacitance >>>>> varicaps? The ones with several hundred pF of range for AM radios. All >>>>> gone lalaland by now? >>>>> Even the ones I found in the 100pF range are either obsolete or not >>>>> recommended for new designs. >>>>> What I am trying to do: I need to control a switcher chip in frequency >>>>> because I've got a very resonant load to deal with. Unfortunately it >>>>> sets the frequency with a timing cap. I'll have to somehow vary that >>>>> between 750pF and 2000pF. Can also be digital but then with a >>>>> granularity of 5pF. The sawtooth voltage across it is 2.5Vpp. >>>>> Doing it with caps and a mux chip or two has its own challenges. The >>>>> ADG-series from AD is around 11pF per pin, otherwise their Rdson is too >>>>> high. Talking about the a rock and a hard spot here. >>>>> Oh, and cost is not very important. If a diode or two or three are >>>>> needed that cost $5 a pop that's ok. >>>> Reading between the lines on the LTC3721-1 datasheet, it seems that the >>>> CT pin generates the upward part of the timing ramp with a (roughly) >>>> 150uA current source. The downward part of the ramp is from a much >>>> stronger current sink. >>>> In an earlier post, Miso suggested sinking some current out of the CT pin >>>> to reduce the frequency, to which you replied "... the chip immediately >>>> gets sea-sick when you do anything DC to that pin." >>>> Had you tried *sourcing* a small (a few uA) current into CT to increase >>>> the frequency? >>>> Regards, >>>> Allan >>> I tried simulating LTC3721 and the charge waveform looks a bit funny, >>> it is >>> ~160uA but at the end of each cycle there's a different ramp upto >>> somtimes -25mA >>> before the 50mA reset pulse >>> adding some current, 10V - 50k, ~doubles the frequency and does not >>> seem to make it go crazy >> Interestingly, that's what I tried a few days ago and it didnt' work. >> Now it does, no funny waveforms. Hmm ... >> > > I wonder what that strange ramping up current sink at the end of each > cycles is? >They do reset the cap with some stiff FET in there once it reaches 2.35V. But I do not have any strange ramping, it looks very clean. When I tried the same before the ramp looked totally sick and it was a circuit I hadn't touched. Weird. But these are only behavioral models so one has to seek a more formal ok from the manufacturer. LTC is pretty good about that. On a previous design I had to pump my feedback straight into the comp node and they said that I could do so. They really talk to the IC folks for such answers. Unfortunately it can take a few days. So I may have to let this one go with the mux and caps in there. -- Regards, Joerg http://www.analogconsultants.com/
Large capacitance varicaps, where are thee?
Started by ●October 22, 2012
Reply by ●October 23, 20122012-10-23
Reply by ●October 23, 20122012-10-23
On Tue, 23 Oct 2012 14:19:16 -0700, Joerg <invalid@invalid.invalid> wrote:>krw@att.bizzzzzzzzzzzz wrote: >> On Tue, 23 Oct 2012 12:45:14 -0700, Joerg <invalid@invalid.invalid> wrote: >> >>> krw@att.bizzzzzzzzzzzz wrote: >>>> On Mon, 22 Oct 2012 18:02:03 -0700, Joerg <invalid@invalid.invalid> wrote: >>>> >>>>> krw@att.bizzzzzzzzzzzz wrote: >>>>>> On Mon, 22 Oct 2012 16:30:01 -0700, Joerg <invalid@invalid.invalid> wrote: >>>>>> >>>>>>> krw@att.bizzzzzzzzzzzz wrote: >>>>>>>> On Mon, 22 Oct 2012 14:22:49 -0700, Joerg <invalid@invalid.invalid> wrote: >>>>>>>> >>>>>>>>> Folks, >>>>>>>>> >>>>>>>>> Looked at Digikey and some others. Where are those huge capacitance >>>>>>>>> varicaps? The ones with several hundred pF of range for AM radios. All >>>>>>>>> gone lalaland by now? >>>>>>>> http://www.angelfire.com/electronic2/index1/VariableCap.html >>>>>>>> >>>>>>>> About half way down. >>>>>>>> >>>>>>>>> Even the ones I found in the 100pF range are either obsolete or not >>>>>>>>> recommended for new designs. >>>>>>>> No kiddin? ;-) >>>>>>>> >>>>>>>>> What I am trying to do: I need to control a switcher chip in frequency >>>>>>>>> because I've got a very resonant load to deal with. Unfortunately it >>>>>>>>> sets the frequency with a timing cap. I'll have to somehow vary that >>>>>>>>> between 750pF and 2000pF. Can also be digital but then with a >>>>>>>>> granularity of 5pF. The sawtooth voltage across it is 2.5Vpp. >>>>>>>> Use a regulator with an external clock. That's what we do (all of our >>>>>>>> switchers are synchronized). >>>>>>>> >>>>>>> Well, I need one from LTC because it must be simulated. The load is >>>>>>> really ugly yet must be well regulated with some unorthodox loop >>>>>>> elements in there. Linear only has the 3721 and 3723 for push-pull. Some >>>>>>> older ones as well but they have the same engine type in them. >>>>>> Nuts. >>>>>> >>>>> What's nuts about this? >>>> Single source because you want a crappy behavioral model to make you feel >>>> good. There *are* other vendors out there, with perfectly good products. >>>> >>> But no simulator models, plus they would also be single-sourced. >> >> Everything is single sourced now so that's an irrelevant argument. >> > >Why did you then flag the single source issue if you think it's irrelevant?Because you refuse to consider any other supplier!>For some of my clients this is relevant. I have used PWM chips in the >past that are 2nd-sourced. From Richtek and TI, for example. But those >tend to be older designs.Jellybeans, perhaps. Nothing leading edge.>>> Some >>> don't have current-mode control and that's a no-no here. >> >> Almost all do. Everything I've used is current-mode. >> > >I am replacing a TI regulator that isn't, and this is one of the reasons.Are you saying5 that TI doesn't have current mode regulators? <boggle> Almost everything I've looked at in the last year is current mode.>>> So far pretty >>> much all my designs came out almost verbatim as simulated. That's the >>> kind of time-to-market clients want. >> >> You trust behaviorals? Amazing. > > >Depends on who made them. From Linear Technology, yes, usually I trust >them. Many years of successful design with their models gives me confidence.I sure don't. I've never seen a behavioral that's good outside it's *NORMAL* operating conditions. That's never where the demons are.
Reply by ●October 23, 20122012-10-23
On Tue, 23 Oct 2012 18:26:46 -0400, rickman <gnuarm@gmail.com> wrote:>On 10/22/2012 10:46 PM, krw@att.bizzzzzzzzzzzz wrote: >> On Mon, 22 Oct 2012 18:02:03 -0700, Joerg<invalid@invalid.invalid> wrote: >>> >>> Well, I can't spend time bench-testing a new switcher chip that doesn't >>> have a decent (meaning behavioral) SPICE model. My stuff usually goes >>> CAD to production these days, with no lab bench time before the >>> prototypes are done. On this one I only had to bench test the load and >>> almost got sick when I looked at the results. >> >> You think you're alone? Get the manufacturer to guarantee the design. > >What good is that? So the board doesn't work like the simulation. Is >the manufacturer going to fix the chip? They might fix the model and >you still miss your schedule.They pay. Big time. Model? You're nuts.
Reply by ●October 23, 20122012-10-23
krw@att.bizzzzzzzzzzzz wrote:> On Tue, 23 Oct 2012 14:19:16 -0700, Joerg <invalid@invalid.invalid> wrote: > >> krw@att.bizzzzzzzzzzzz wrote: >>> On Tue, 23 Oct 2012 12:45:14 -0700, Joerg <invalid@invalid.invalid> wrote: >>> >>>> krw@att.bizzzzzzzzzzzz wrote: >>>>> On Mon, 22 Oct 2012 18:02:03 -0700, Joerg <invalid@invalid.invalid> wrote: >>>>> >>>>>> krw@att.bizzzzzzzzzzzz wrote: >>>>>>> On Mon, 22 Oct 2012 16:30:01 -0700, Joerg <invalid@invalid.invalid> wrote: >>>>>>> >>>>>>>> krw@att.bizzzzzzzzzzzz wrote: >>>>>>>>> On Mon, 22 Oct 2012 14:22:49 -0700, Joerg <invalid@invalid.invalid> wrote: >>>>>>>>> >>>>>>>>>> Folks, >>>>>>>>>> >>>>>>>>>> Looked at Digikey and some others. Where are those huge capacitance >>>>>>>>>> varicaps? The ones with several hundred pF of range for AM radios. All >>>>>>>>>> gone lalaland by now? >>>>>>>>> http://www.angelfire.com/electronic2/index1/VariableCap.html >>>>>>>>> >>>>>>>>> About half way down. >>>>>>>>> >>>>>>>>>> Even the ones I found in the 100pF range are either obsolete or not >>>>>>>>>> recommended for new designs. >>>>>>>>> No kiddin? ;-) >>>>>>>>> >>>>>>>>>> What I am trying to do: I need to control a switcher chip in frequency >>>>>>>>>> because I've got a very resonant load to deal with. Unfortunately it >>>>>>>>>> sets the frequency with a timing cap. I'll have to somehow vary that >>>>>>>>>> between 750pF and 2000pF. Can also be digital but then with a >>>>>>>>>> granularity of 5pF. The sawtooth voltage across it is 2.5Vpp. >>>>>>>>> Use a regulator with an external clock. That's what we do (all of our >>>>>>>>> switchers are synchronized). >>>>>>>>> >>>>>>>> Well, I need one from LTC because it must be simulated. The load is >>>>>>>> really ugly yet must be well regulated with some unorthodox loop >>>>>>>> elements in there. Linear only has the 3721 and 3723 for push-pull. Some >>>>>>>> older ones as well but they have the same engine type in them. >>>>>>> Nuts. >>>>>>> >>>>>> What's nuts about this? >>>>> Single source because you want a crappy behavioral model to make you feel >>>>> good. There *are* other vendors out there, with perfectly good products. >>>>> >>>> But no simulator models, plus they would also be single-sourced. >>> Everything is single sourced now so that's an irrelevant argument. >>> >> Why did you then flag the single source issue if you think it's irrelevant? > > Because you refuse to consider any other supplier! >That's not the definition of single source :-) I do use others, just not for really critical stuff like this where simulation is key.>> For some of my clients this is relevant. I have used PWM chips in the >> past that are 2nd-sourced. From Richtek and TI, for example. But those >> tend to be older designs. > > Jellybeans, perhaps. Nothing leading edge. > >>>> Some >>>> don't have current-mode control and that's a no-no here. >>> Almost all do. Everything I've used is current-mode. >>> >> I am replacing a TI regulator that isn't, and this is one of the reasons. > > Are you saying5 that TI doesn't have current mode regulators? <boggle> Almost > everything I've looked at in the last year is current mode. >Huh? That's not what I said. I said I am replacing a TI regulator that is not current-mode. It has to go because that one isn't up to the job. Of course they have developed better ones by now. But no behavioral models so one cannot simulate in a reasonable time frame.>>>> So far pretty >>>> much all my designs came out almost verbatim as simulated. That's the >>>> kind of time-to-market clients want. >>> You trust behaviorals? Amazing. >> >> Depends on who made them. From Linear Technology, yes, usually I trust >> them. Many years of successful design with their models gives me confidence. > > I sure don't. I've never seen a behavioral that's good outside it's *NORMAL* > operating conditions. That's never where the demons are. >Then you haven't tried hard enough with LTSpice :-) By now they know me at LTC for lots of unorthodox uses. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●October 23, 20122012-10-23
On 10/23/2012 8:30 PM, krw@att.bizzzzzzzzzzzz wrote:> On Tue, 23 Oct 2012 18:26:46 -0400, rickman<gnuarm@gmail.com> wrote: > >> On 10/22/2012 10:46 PM, krw@att.bizzzzzzzzzzzz wrote: >>> On Mon, 22 Oct 2012 18:02:03 -0700, Joerg<invalid@invalid.invalid> wrote: >>>> >>>> Well, I can't spend time bench-testing a new switcher chip that doesn't >>>> have a decent (meaning behavioral) SPICE model. My stuff usually goes >>>> CAD to production these days, with no lab bench time before the >>>> prototypes are done. On this one I only had to bench test the load and >>>> almost got sick when I looked at the results. >>> >>> You think you're alone? Get the manufacturer to guarantee the design. >> >> What good is that? So the board doesn't work like the simulation. Is >> the manufacturer going to fix the chip? They might fix the model and >> you still miss your schedule. > > They pay. Big time. Model? You're nuts.Hah! Pay!!! LOL!!! Good luck getting a chip maker to guarantee YOUR design no matter what you do. Rick
Reply by ●October 23, 20122012-10-23
On Tue, 23 Oct 2012 17:49:19 -0700, Joerg <invalid@invalid.invalid> wrote:>krw@att.bizzzzzzzzzzzz wrote: >> On Tue, 23 Oct 2012 14:19:16 -0700, Joerg <invalid@invalid.invalid> wrote: >> >>> krw@att.bizzzzzzzzzzzz wrote: >>>> On Tue, 23 Oct 2012 12:45:14 -0700, Joerg <invalid@invalid.invalid> wrote: >>>> >>>>> krw@att.bizzzzzzzzzzzz wrote: >>>>>> On Mon, 22 Oct 2012 18:02:03 -0700, Joerg <invalid@invalid.invalid> wrote: >>>>>> >>>>>>> krw@att.bizzzzzzzzzzzz wrote: >>>>>>>> On Mon, 22 Oct 2012 16:30:01 -0700, Joerg <invalid@invalid.invalid> wrote: >>>>>>>> >>>>>>>>> krw@att.bizzzzzzzzzzzz wrote: >>>>>>>>>> On Mon, 22 Oct 2012 14:22:49 -0700, Joerg <invalid@invalid.invalid> wrote: >>>>>>>>>> >>>>>>>>>>> Folks, >>>>>>>>>>> >>>>>>>>>>> Looked at Digikey and some others. Where are those huge capacitance >>>>>>>>>>> varicaps? The ones with several hundred pF of range for AM radios. All >>>>>>>>>>> gone lalaland by now? >>>>>>>>>> http://www.angelfire.com/electronic2/index1/VariableCap.html >>>>>>>>>> >>>>>>>>>> About half way down. >>>>>>>>>> >>>>>>>>>>> Even the ones I found in the 100pF range are either obsolete or not >>>>>>>>>>> recommended for new designs. >>>>>>>>>> No kiddin? ;-) >>>>>>>>>> >>>>>>>>>>> What I am trying to do: I need to control a switcher chip in frequency >>>>>>>>>>> because I've got a very resonant load to deal with. Unfortunately it >>>>>>>>>>> sets the frequency with a timing cap. I'll have to somehow vary that >>>>>>>>>>> between 750pF and 2000pF. Can also be digital but then with a >>>>>>>>>>> granularity of 5pF. The sawtooth voltage across it is 2.5Vpp. >>>>>>>>>> Use a regulator with an external clock. That's what we do (all of our >>>>>>>>>> switchers are synchronized). >>>>>>>>>> >>>>>>>>> Well, I need one from LTC because it must be simulated. The load is >>>>>>>>> really ugly yet must be well regulated with some unorthodox loop >>>>>>>>> elements in there. Linear only has the 3721 and 3723 for push-pull. Some >>>>>>>>> older ones as well but they have the same engine type in them. >>>>>>>> Nuts. >>>>>>>> >>>>>>> What's nuts about this? >>>>>> Single source because you want a crappy behavioral model to make you feel >>>>>> good. There *are* other vendors out there, with perfectly good products. >>>>>> >>>>> But no simulator models, plus they would also be single-sourced. >>>> Everything is single sourced now so that's an irrelevant argument. >>>> >>> Why did you then flag the single source issue if you think it's irrelevant? >> >> Because you refuse to consider any other supplier! >> > >That's not the definition of single source :-)You only consider one source. That *is* a single source. Nuts!>I do use others, just not for really critical stuff like this where >simulation is key.With a behavioral, you can only simulate what the model builder anticipated. Again, that's rarely where the demons be. At least with full models, you have a chance.>>> For some of my clients this is relevant. I have used PWM chips in the >>> past that are 2nd-sourced. From Richtek and TI, for example. But those >>> tend to be older designs. >> >> Jellybeans, perhaps. Nothing leading edge. >> >>>>> Some >>>>> don't have current-mode control and that's a no-no here. >>>> Almost all do. Everything I've used is current-mode. >>>> >>> I am replacing a TI regulator that isn't, and this is one of the reasons. >> >> Are you saying5 that TI doesn't have current mode regulators? <boggle> Almost >> everything I've looked at in the last year is current mode. >> > >Huh? That's not what I said. I said I am replacing a TI regulator that >is not current-mode. It has to go because that one isn't up to the job. >Of course they have developed better ones by now. But no behavioral >models so one cannot simulate in a reasonable time frame.Yet you will only use LTC because they're current mode. <boggle>>>>>> So far pretty >>>>> much all my designs came out almost verbatim as simulated. That's the >>>>> kind of time-to-market clients want. >>>> You trust behaviorals? Amazing. >>> >>> Depends on who made them. From Linear Technology, yes, usually I trust >>> them. Many years of successful design with their models gives me confidence. >> >> I sure don't. I've never seen a behavioral that's good outside it's *NORMAL* >> operating conditions. That's never where the demons are. >> > >Then you haven't tried hard enough with LTSpice :-)Nonsense.>By now they know me at LTC for lots of unorthodox uses.The models are useless outside their limited operational area. IOW, useless for guaranteeing operation.
Reply by ●October 23, 20122012-10-23
On Tue, 23 Oct 2012 21:05:00 -0400, rickman <gnuarm@gmail.com> wrote:>On 10/23/2012 8:30 PM, krw@att.bizzzzzzzzzzzz wrote: >> On Tue, 23 Oct 2012 18:26:46 -0400, rickman<gnuarm@gmail.com> wrote: >> >>> On 10/22/2012 10:46 PM, krw@att.bizzzzzzzzzzzz wrote: >>>> On Mon, 22 Oct 2012 18:02:03 -0700, Joerg<invalid@invalid.invalid> wrote: >>>>> >>>>> Well, I can't spend time bench-testing a new switcher chip that doesn't >>>>> have a decent (meaning behavioral) SPICE model. My stuff usually goes >>>>> CAD to production these days, with no lab bench time before the >>>>> prototypes are done. On this one I only had to bench test the load and >>>>> almost got sick when I looked at the results. >>>> >>>> You think you're alone? Get the manufacturer to guarantee the design. >>> >>> What good is that? So the board doesn't work like the simulation. Is >>> the manufacturer going to fix the chip? They might fix the model and >>> you still miss your schedule. >> >> They pay. Big time. Model? You're nuts. > >Hah! Pay!!! LOL!!!You are an idiot.>Good luck getting a chip maker to guarantee YOUR design no matter what >you do.You're batting 1000 today. Go back to your g5eometry lessons, with Bloggs.
Reply by ●October 24, 20122012-10-24
"Joerg" <invalid@invalid.invalid> wrote in message news:aeooufFmtb0U1@mid.individual.net...> They do reset the cap with some stiff FET in there once it reaches > 2.35V. But I do not have any strange ramping, it looks very clean. When > I tried the same before the ramp looked totally sick and it was a > circuit I hadn't touched. Weird.It wasn't on trapezoidal integration, was it? :-o Sounds like the kind of gobbledeygook you get from funny simulation settings (or funny models that need more than default fudging!). Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
Reply by ●October 24, 20122012-10-24
krw@att.bizzzzzzzzzzzz wrote:> On Tue, 23 Oct 2012 17:49:19 -0700, Joerg <invalid@invalid.invalid> wrote: > >> krw@att.bizzzzzzzzzzzz wrote: >>> On Tue, 23 Oct 2012 14:19:16 -0700, Joerg <invalid@invalid.invalid> wrote: >>> >>>> krw@att.bizzzzzzzzzzzz wrote: >>>>> On Tue, 23 Oct 2012 12:45:14 -0700, Joerg <invalid@invalid.invalid> wrote: >>>>> >>>>>> krw@att.bizzzzzzzzzzzz wrote:[...]>> I do use others, just not for really critical stuff like this where >> simulation is key. > > With a behavioral, you can only simulate what the model builder anticipated. > Again, that's rarely where the demons be. At least with full models, you have > a chance. >Yep. Last time I did that one single run too about four (!) hours.>>>> For some of my clients this is relevant. I have used PWM chips in the >>>> past that are 2nd-sourced. From Richtek and TI, for example. But those >>>> tend to be older designs. >>> Jellybeans, perhaps. Nothing leading edge. >>> >>>>>> Some >>>>>> don't have current-mode control and that's a no-no here. >>>>> Almost all do. Everything I've used is current-mode. >>>>> >>>> I am replacing a TI regulator that isn't, and this is one of the reasons. >>> Are you saying5 that TI doesn't have current mode regulators? <boggle> Almost >>> everything I've looked at in the last year is current mode. >>> >> Huh? That's not what I said. I said I am replacing a TI regulator that >> is not current-mode. It has to go because that one isn't up to the job. >> Of course they have developed better ones by now. But no behavioral >> models so one cannot simulate in a reasonable time frame. > > Yet you will only use LTC because they're current mode. <boggle> >You are not correctly reading what I write. I am using LTC because there are models that allow fast simulation. _Not_ because they are current mode. I only require that any switcher that replaces the old one is current mode.>>>>>> So far pretty >>>>>> much all my designs came out almost verbatim as simulated. That's the >>>>>> kind of time-to-market clients want. >>>>> You trust behaviorals? Amazing. >>>> Depends on who made them. From Linear Technology, yes, usually I trust >>>> them. Many years of successful design with their models gives me confidence. >>> I sure don't. I've never seen a behavioral that's good outside it's *NORMAL* >>> operating conditions. That's never where the demons are. >>> >> Then you haven't tried hard enough with LTSpice :-) > > Nonsense. > >> By now they know me at LTC for lots of unorthodox uses. > > The models are useless outside their limited operational area. IOW, useless > for guaranteeing operation. >Sorry, but I have proven that statement wrong many times. For that to work you do need to establish good connections to their engineers though. I have. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●October 24, 20122012-10-24
Tim Williams wrote:> "Joerg" <invalid@invalid.invalid> wrote in message > news:aeooufFmtb0U1@mid.individual.net... >> They do reset the cap with some stiff FET in there once it reaches >> 2.35V. But I do not have any strange ramping, it looks very clean. When >> I tried the same before the ramp looked totally sick and it was a >> circuit I hadn't touched. Weird. > > It wasn't on trapezoidal integration, was it? :-o Sounds like the kind > of gobbledeygook you get from funny simulation settings (or funny models > that need more than default fudging!). >Well, like with all unorthodox uses of such chips I want to get a blessing from their IC designers. Usually takes about a week, then they say yea or nay. Those guys know. -- Regards, Joerg http://www.analogconsultants.com/
