MC34063 with small inductors
in [Design]
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From: Jim Thompson on 8 Apr 2010 13:12 On Thu, 08 Apr 2010 10:08:49 -0700, Joerg <invalid(a)invalid.invalid> wrote: >dagmargoodboat(a)yahoo.com wrote: >> On Apr 7, 9:48 pm, Joerg <inva...(a)invalid.invalid> wrote: >>> dagmargoodb...(a)yahoo.com wrote: >>>> On Apr 7, 7:06 pm, Joerg <inva...(a)invalid.invalid> wrote: >> >>>>> There's actually three more models around but they essentially behave >>>>> similar. Thing is, the chip is not supposed to turn off the switch >>>>> during the positive ramp because the comparator does not tie into the >>>>> reset input of the register, only the set input. >>>>> <scratching_ head> >>>> 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? ...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
From: Joerg on 8 Apr 2010 13:46 Jim Thompson wrote: > On Thu, 08 Apr 2010 10:08:49 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> dagmargoodboat(a)yahoo.com wrote: >>> On Apr 7, 9:48 pm, Joerg <inva...(a)invalid.invalid> wrote: >>>> dagmargoodb...(a)yahoo.com wrote: >>>>> On Apr 7, 7:06 pm, Joerg <inva...(a)invalid.invalid> wrote: >>>>>> There's actually three more models around but they essentially behave >>>>>> similar. Thing is, the chip is not supposed to turn off the switch >>>>>> during the positive ramp because the comparator does not tie into the >>>>>> reset input of the register, only the set input. >>>>>> <scratching_ head> >>>>> 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. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Hammy on 8 Apr 2010 14:20 On Thu, 08 Apr 2010 10:46:22 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Jim Thompson wrote: >> On Thu, 08 Apr 2010 10:08:49 -0700, Joerg <invalid(a)invalid.invalid> >> wrote: >> >>> dagmargoodboat(a)yahoo.com wrote: >>>> On Apr 7, 9:48 pm, Joerg <inva...(a)invalid.invalid> wrote: >>>>> dagmargoodb...(a)yahoo.com wrote: >>>>>> On Apr 7, 7:06 pm, Joerg <inva...(a)invalid.invalid> wrote: >>>>>>> There's actually three more models around but they essentially behave >>>>>>> similar. Thing is, the chip is not supposed to turn off the switch >>>>>>> during the positive ramp because the comparator does not tie into the >>>>>>> reset input of the register, only the set input. >>>>>>> <scratching_ head> >>>>>> 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. I have a NCP3063 Buck on a Breadboard now. I'm using it to test cross-regulation on a coupled inductor (+/- 5V out). It only terminates on the falling edge of Ct. See scope shot. Ct ramp and switch node same as Jorge's sim. http://i42.tinypic.com/34nlitw.jpg You can see the glitch on the Ct ramp when the switch changes states. Joerg I used the MC33063 for a 15W DCM buck before, it was the first SMPS I did on a PCB in college and it ran fine. Mind you it needed 3 x 1mF of output capacitance to get the ripple down to something reasonable. The inductor was 12uH for 5V out at 3A; 15 to 20Vin, 60kHz. The peak current was a little over 6A ;-) using an external P-Fet. I think the only reason they don't show or recommend DCM is because the already high and modulated ripple you get with Hysteretic type converters is much worse in DCM particularly at higher power levels. This isn't flattering for their IC so they just show CCM examples. Just my thoughts. Here is the output ripple 12Vin, 5V out, 0.4A. This is with a 220uH inductor and a 330uF PSA POLYMER output cap. Doing a proper PCB and a small LC filter (bead MLCC) would get rid of those HF oscillations http://i41.tinypic.com/2mebbya.jpg This is using the NCP3063 at 175kHz
From: Joerg on 8 Apr 2010 14:32 Hammy wrote: > On Thu, 08 Apr 2010 10:46:22 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> Jim Thompson wrote: >>> On Thu, 08 Apr 2010 10:08:49 -0700, Joerg <invalid(a)invalid.invalid> >>> wrote: >>> >>>> dagmargoodboat(a)yahoo.com wrote: >>>>> On Apr 7, 9:48 pm, Joerg <inva...(a)invalid.invalid> wrote: >>>>>> dagmargoodb...(a)yahoo.com wrote: >>>>>>> On Apr 7, 7:06 pm, Joerg <inva...(a)invalid.invalid> wrote: >>>>>>>> There's actually three more models around but they essentially behave >>>>>>>> similar. Thing is, the chip is not supposed to turn off the switch >>>>>>>> during the positive ramp because the comparator does not tie into the >>>>>>>> reset input of the register, only the set input. >>>>>>>> <scratching_ head> >>>>>>> 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. > > I have a NCP3063 Buck on a Breadboard now. I'm using it to test > cross-regulation on a coupled inductor (+/- 5V out). It only > terminates on the falling edge of Ct. > > See scope shot. Ct ramp and switch node same as Jorge's sim. > > http://i42.tinypic.com/34nlitw.jpg > > You can see the glitch on the Ct ramp when the switch changes states. > Thanks, Hammy. If you never see it turn off before the peak ramp reversal then it behaves according to the datasheet. That would mean the SPICE model isn't quite up to snuff or LTSpice misinterprets something in there. > Joerg I used the MC33063 for a 15W DCM buck before, it was the first > SMPS I did on a PCB in college and it ran fine. Mind you it needed 3 x > 1mF of output capacitance to get the ripple down to something > reasonable. The inductor was 12uH for 5V out at 3A; 15 to 20Vin, > 60kHz. The peak current was a little over 6A ;-) using an external > P-Fet. > 3000uF on the output? Yikes! I don't even have that much on the rectifier after the mains transformer. > I think the only reason they don't show or recommend DCM is because > the already high and modulated ripple you get with Hysteretic type > converters is much worse in DCM particularly at higher power levels. > This isn't flattering for their IC so they just show CCM examples. > Just my thoughts. > > Here is the output ripple 12Vin, 5V out, 0.4A. This is with a 220uH > inductor and a 330uF PSA POLYMER output cap. Doing a proper PCB and a > small LC filter (bead MLCC) would get rid of those HF oscillations > > http://i41.tinypic.com/2mebbya.jpg > > This is using the NCP3063 at 175kHz The RF is fairly easy to lowpass out but the lower frequency ripple from the slightly hysteretic behavior of this chip drops in spectrum a lot the higher the inductance and the larger the output cap. But in this app we can live with it since that rail is only used for relay drivers. There's another regulator downstream for sensitive stuff. I don't think I'll be able to keep it in DCM considering the cramped space I've got on the board. Thanks for posting the scope shots, looks encouraging :-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Jim Thompson on 8 Apr 2010 15:33
On Thu, 08 Apr 2010 10:46:22 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Jim Thompson wrote: >> On Thu, 08 Apr 2010 10:08:49 -0700, Joerg <invalid(a)invalid.invalid> >> wrote: >> >>> dagmargoodboat(a)yahoo.com wrote: >>>> On Apr 7, 9:48 pm, Joerg <inva...(a)invalid.invalid> wrote: >>>>> dagmargoodb...(a)yahoo.com wrote: >>>>>> On Apr 7, 7:06 pm, Joerg <inva...(a)invalid.invalid> wrote: >>>>>>> There's actually three more models around but they essentially behave >>>>>>> similar. Thing is, the chip is not supposed to turn off the switch >>>>>>> during the positive ramp because the comparator does not tie into the >>>>>>> reset input of the register, only the set input. >>>>>>> <scratching_ head> >>>>>> 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? ...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 |