MC34063 with small inductors
in [Design]
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From: Michael A. Terrell on 8 Apr 2010 19:45 John Larkin wrote: > > Funny that RST can't learn how to FRIKKIN learn how to bottom-post. You just can't fix stupid. :( -- Lead free solder is Belgium's version of 'Hold my beer and watch this!'
From: miso on 8 Apr 2010 19:53 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? 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.
From: dagmargoodboat on 9 Apr 2010 08:00 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. :-) -- Cheers, James Arthur
From: Joerg on 9 Apr 2010 10:31 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 :-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Jim Thompson on 9 Apr 2010 10:34
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? ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy |