MC34063 with small inductors
in [Design]
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From: Joerg on 9 Apr 2010 10:35 miso(a)sushi.com wrote: > On Apr 7, 9:02 am, Joerg <inva...(a)invalid.invalid> wrote: >> Grant wrote: >>> On Tue, 06 Apr 2010 18:00:41 -0700, Joerg <inva...(a)invalid.invalid> wrote: >>>> Hello Folks, >>>> Have to correct a design with a 34063 in there. Buck, VIN 16-30V, VOUT >>>> slightly under 12V, 400mA max output. And no, I don't like it much :-) >>>> One of the issues is a saturating inductor. Can't change the layout and >>>> to be able to cram one in there I probably have to drop down to 47uH, >>>> maybe 68uH if lucky. >>>> SPICE says it's ok but none of the datasheets or app notes recommends >>>> going that low. Any reason why not? >>> Try the NCP3063 from On Semi, it's a faster pin compatible for 34063 >> Thanks! Technically I can't change it but if needed it's needed. It's >> only 50% faster but maybe that helps here. >> >> -- >> Regards, Joerg >> >> http://www.analogconsultants.com/ >> >> "gmail" domain blocked because of excessive spam. >> Use another domain or send PM. > > Geez these threads get messy. First of all, have you called apps? > Not yet, another more pressing problem came up. Other client, other chip. That one behaves ok in the sims but doesn't behave like the datasheet says in real life. Hurumph ... > Generally if there is a limit, there is science behind that limit. But > in the chip biz, you have to pick limits that WILL work for the tens > of millions of parts you crank out. Probably more for this part. So > you get it to work in spice, but they fab a "slow" boat of wafer that > is still within spec, and the thing doesn't work. Now if your volume > is low and you temperature test your boards, I wouldn't be too > concerned with using an external component a bit out of the spec > limit. Again, I am _not_ operating the thing outside its spec limits. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Joerg on 9 Apr 2010 10:42 Jim Thompson wrote: > On Fri, 09 Apr 2010 07:31:15 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> dagmargoodboat(a)yahoo.com wrote: >>> On Apr 8, 2:41 pm, Joerg <inva...(a)invalid.invalid> wrote: >>>> Jim Thompson wrote: >>>>> On Thu, 08 Apr 2010 10:46:22 -0700, Joerg <inva...(a)invalid.invalid> >>>>> wrote: >>>>>> Jim Thompson wrote: >>>>>>> On Thu, 08 Apr 2010 10:08:49 -0700, Joerg <inva...(a)invalid.invalid> >>>>>>> wrote: >>>>>>>> dagmargoodb...(a)yahoo.com wrote: >>>>>>>>> On Apr 7, 9:48 pm, Joerg <inva...(a)invalid.invalid> wrote: >>>>>>>>>> dagmargoodb...(a)yahoo.com wrote: >>>>>>>>>>> Yeah. I read TI's app note. So it can start an ON cycle any time >>>>>>>>>>> during ramp up, but can't ever stop until ramp-down. Crude. Burp, >>>>>>>>>>> sputter, and cough, in this application. >>>>>>>>>> Well, if it did that I'd be happy. But it does cut during ramp-down and >>>>>>>>>> according to the internal wire-up it's not supposed to. Helmut >>>>>>>>>> Sennewald, one of the LTSpice gurus, could not reproduce the error I >>>>>>>>>> saw. Sent him my file, so we'll see. >>>>>>>>> It's s'posed to cut off during ramp-down--that's when the flop gets >>>>>>>>> reset, unconditionally. So says TI, anyhow. >>>>>>>>> http://focus.ti.com/lit/an/slva252b/slva252b.pdf >>>>>>>>> the operative paragraph being the last one pg. 5. And, the last >>>>>>>>> comment in Table 1 confirms: >>>>>>>>> "Output switch conduction is always >>>>>>>>> terminated when Ct is ramping down." >>>>>>>> I know but as shown in my sim plot if is terminated before Ct is ramping >>>>>>>> down. That not s'posed to happen. But does, at least according to SPICE. >>>>>>> What does it do in the lab? >>>>>> I don't know yet. The package just arrived but I have a much more >>>>>> pressing problem from an other client to deal with right now. Also a >>>>>> chip that seems to not exactly do what I think it should. For that one >>>>>> we have lab bench scope plots and the manufacturer is investigating. >>>>>> This one simulates alright but chokes in real life. >>>>> Is it happening simultaneous with _on-set_ of ramp-down? >>>> On the 34063? I have simulated the dickens out of that and the >>>> comparator never shuts off the switch at onset, just occasionally in the >>>> middle of a ramp-up which it ain't supposed to be able to do. And in >>>> Hammy's case doesn't do. >>> Propagation delay? When the ramp comparator trips, it'll take a >>> minute or two to turn the timing ramp current source around. So to >>> speak. :-) >>> >> That was a good one. Maybe there's a bureaucrat in the chip and the >> comparator needs request a permit every time it trips :-) > > Are you trying to run it faster than spec? Faster rise times > capacitively tripping a comparator? > No, in that mode it's actually running way slower than spec, around 30kHz while spec says 100kHz possible. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: John Larkin on 9 Apr 2010 11:36 On Fri, 9 Apr 2010 05:00:10 -0700 (PDT), dagmargoodboat(a)yahoo.com wrote: >On Apr 8, 2:41�pm, Joerg <inva...(a)invalid.invalid> wrote: >> Jim Thompson wrote: >> > On Thu, 08 Apr 2010 10:46:22 -0700, Joerg <inva...(a)invalid.invalid> >> > wrote: >> >> >> Jim Thompson wrote: >> >>> On Thu, 08 Apr 2010 10:08:49 -0700, Joerg <inva...(a)invalid.invalid> >> >>> wrote: >> >> >>>> dagmargoodb...(a)yahoo.com wrote: >> >>>>> On Apr 7, 9:48 pm, Joerg <inva...(a)invalid.invalid> wrote: >> >>>>>> dagmargoodb...(a)yahoo.com wrote: > >> >>>>>>> Yeah. �I read TI's app note. �So it can start an ON cycle any time >> >>>>>>> during ramp up, but can't ever stop until ramp-down. �Crude. �Burp, >> >>>>>>> sputter, and cough, in this application. >> >>>>>> >> >>>>>> Well, if it did that I'd be happy. But it does cut during ramp-down and >> >>>>>> according to the internal wire-up it's not supposed to. Helmut >> >>>>>> Sennewald, one of the LTSpice gurus, could not reproduce the error I >> >>>>>> saw. Sent him my file, so we'll see. >> >>>>> >> >>>>> It's s'posed to cut off during ramp-down--that's when the flop gets >> >>>>> reset, unconditionally. �So says TI, anyhow. >> >> >>>>>http://focus.ti.com/lit/an/slva252b/slva252b.pdf >> >> >>>>> the operative paragraph being the last one pg. 5. �And, the last >> >>>>> comment in Table 1 confirms: >> >> >>>>> �"Output switch conduction is always >> >>>>> � terminated when Ct is ramping down." >> >> >>>> I know but as shown in my sim plot if is terminated before Ct is ramping >> >>>> down. That not s'posed to happen. But does, at least according to SPICE. >> >>> >> >>> What does it do in the lab? >> >> >> I don't know yet. The package just arrived but I have a much more >> >> pressing problem from an other client to deal with right now. Also a >> >> chip that seems to not exactly do what I think it should. For that one >> >> we have lab bench scope plots and the manufacturer is investigating. >> >> This one simulates alright but chokes in real life. >> >> > Is it happening simultaneous with _on-set_ of ramp-down? >> >> On the 34063? I have simulated the dickens out of that and the >> comparator never shuts off the switch at onset, just occasionally in the >> middle of a ramp-up which it ain't supposed to be able to do. And in >> Hammy's case doesn't do. > >Propagation delay? When the ramp comparator trips, it'll take a >minute or two to turn the timing ramp current source around. So to >speak. :-) We're using some tiny 3 MHz switchers now. I think I've seen datasheets on 10 MHz switchers. The power isolators inside the ADI powered data isolators run at 300 MHz, I think. John
From: dagmargoodboat on 9 Apr 2010 12:01 On Apr 9, 10:36 am, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Fri, 9 Apr 2010 05:00:10 -0700 (PDT), dagmargoodb...(a)yahoo.com > wrote: > > >On Apr 8, 2:41 pm, Joerg <inva...(a)invalid.invalid> wrote: > >> On the 34063? I have simulated the dickens out of that and the > >> comparator never shuts off the switch at onset, just occasionally in the > >> middle of a ramp-up which it ain't supposed to be able to do. And in > >> Hammy's case doesn't do. > > >Propagation delay? When the ramp comparator trips, it'll take a > >minute or two to turn the timing ramp current source around. So to > >speak. :-) > > We're using some tiny 3 MHz switchers now. Two orders of magnitude faster than the MC34063. Sweet. Aren't core and skin losses deadly? I've done 300KHz, discrete, but 50KHz-ish is usually more efficient. -- Cheers, James Arthur
From: John Larkin on 9 Apr 2010 12:28
On Fri, 9 Apr 2010 09:01:36 -0700 (PDT), dagmargoodboat(a)yahoo.com wrote: >On Apr 9, 10:36�am, John Larkin ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> On Fri, 9 Apr 2010 05:00:10 -0700 (PDT), dagmargoodb...(a)yahoo.com >> wrote: >> >> >On Apr 8, 2:41�pm, Joerg <inva...(a)invalid.invalid> wrote: > >> >> On the 34063? I have simulated the dickens out of that and the >> >> comparator never shuts off the switch at onset, just occasionally in the >> >> middle of a ramp-up which it ain't supposed to be able to do. And in >> >> Hammy's case doesn't do. >> >> >Propagation delay? �When the ramp comparator trips, it'll take a >> >minute or two to turn the timing ramp current source around. �So to >> >speak. :-) >> >> We're using some tiny 3 MHz switchers now. > >Two orders of magnitude faster than the MC34063. Sweet. Aren't core >and skin losses deadly? The compensation is that you need very little copper and ferrite at 3 MHz. John |