[SI-LIST] Re: ESR too low?
- From: steve weir <weirsi@xxxxxxxxxx>
- To: dp@xxxxxxxxxxx, <si-list@xxxxxxxxxxxxx>
- Date: Wed, 09 Nov 2005 21:16:41 -0800
Dimiter, I've got to disagree there. While it did take almost 20 years for
the SMPS IC makers to discover the joys of constant on and constant off
time parts, ( a '123 to you, a CMOS 555, or digital counter off a high
speed clock to others ), they have been available now for several
years. LTC has several very nice parts. I hope the POLA guys update with
these, because right now the POLA converters have really mediocre
responses. Transient responses for these controllers are one to two orders
of magnitude ( a couple to a few cycles for full recovery ) faster than
constant frequency units you rightfully disdain. As a result, the
effective inductance is much smaller, and they remain stable with much
lower ESR caps than constant frequency controllers.
This newer breed of controller have a lot more housekeeping functions than
you will get with a home grown comparator / op-amp / one-shot
solution. And the control function in a little SSOP or SSOIC is going to
be a whole lot smaller as well, with less opportunity for stray pick-up and
other issues multi chip solutions impose. New entrants into the field
are offering digitally controlled loops with some impressive specs as
well. It would be nice if these parts were also very cheap, but we know
better than to expect that.
Steve.
At 11:32 PM 11/9/2005 +0300, Dimiter Popoff wrote:
>About 15 (if not 20...) years ago, I could not find a suitable off-the-shelf
>flyback convertor chip so I designed it using a 74HC123 and an opamp.
>
> One of the benefits of having the opamp outside allowed me to
>put a non-linear feedback, consisting of a group of forward biased
>diodes in the feedback path. The result was fast response to
>large changes and stablity (being slower when no transients) the
>rest of the time.
> Of course, it is again all about the numbers, one has to do his job.
>
> Over the years, I have been looking around for some readily available
>single-chip replacement of this circuit. For some mainstream applications,
>I have been able to find something. However, I had to design the 123 +lmc6482
>in a board this very year again, there was just no comparable choice...
>Amazing how long some things take sometimes..
>
>Dimiter
>
>------------------------------------------------------
>Dimiter Popoff Transgalactic Instruments
>
>http://www.tgi-sci.com
>------------------------------------------------------
>
>
>
>
> > -------Original Message-------
> > From: Henson, Bradley S <Bradley.S.Henson@xxxxxxxxxx>
> > Subject: [SI-LIST] Re: ESR too low?
> > Sent: Nov 09 '05 22:57
> >
> > It's all in the numbers. I just went and looked at these parts on their
> > site. I looked at a 30A model. It mandated 470uF each on the input AND
> > output to meet the specs. So right off the bat, they are stipulating
> > almost 1000uF of bulk capacitance. A fairly slow 50% load step causes
> > 150mV noise (not good enough for my stuff). Looks like the loop response
> > is 50us and it is switching at 470KHz: There is a limit to what can be
> > done. I'm not knocking their regulators at all, just saying each person
> > needs to work through their real application numbers. I don't see my
> > need for low esr bulk decoupling going away real soon :)
> >
> > -----Original Message-----
> > From: Calvo, Oscar A (FL51) [mailto:Oscar.A.Calvo@xxxxxxxxxxxxx]=20
> > Sent: Wednesday, November 09, 2005 11:30 AM
> > To: Henson, Bradley S; si-list@xxxxxxxxxxxxx
> > Subject: RE: [SI-LIST] Re: ESR too low?
> >
> >
> >
> > In one of their slides they showed that you could actually get rid of
> > the tantalum bulk capacitors altogether by using this Turbo Trans
> > feature and by increasing the total ceramic capacitance.
> >
> >
> > -----Original Message-----
> > From: Henson, Bradley S [mailto:Bradley.S.Henson@xxxxxxxxxx]=20
> > Sent: Wednesday, November 09, 2005 2:17 PM
> > To: Oscar.A.Calvo@xxxxxxxxxxxxx; electronbob2@xxxxxxxxxxxxx;
> > matusov@xxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
> > Subject: RE: [SI-LIST] Re: ESR too low?
> >
> > This is an interesting problem. Modern high current/low voltage chips
> > require giant step load currents (e.g. 25A) at very low impedance to
> > stay within voltage tolerance. Regulators take hundreds of ns or
> > microseconds to respond to load transients. This drives us to need very
> > low esr bulk caps to supply virtually all of the demand while the
> > regulator loop responds. If you speed up the regulator response, you
> > simply move the transient problem to the input of the regulator, albeit
> > there should be more noise tolerance there possibly. I would also think
> > you are not going to be able to get rid of the need for a considerable
> > amount of very low esr bulk capacitance even with pretty fast response
> > times, at least with the regulator speeds I've seen.
> >
> > -----Original Message-----
> > From: Calvo, Oscar A (FL51) [mailto:Oscar.A.Calvo@xxxxxxxxxxxxx]=20
> > Sent: Wednesday, November 09, 2005 10:58 AM
> > To: electronbob2@xxxxxxxxxxxxx; matusov@xxxxxxxxxxxx;
> > si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Re: ESR too low?
> >
> >
> >
> > I just attended a TI Web-seminar in where they talked about their new
> > line of PTH power modules which include a new feature that they call
> > Turbo Trans. Turbo Trans allows the user to custom tune the module to
> > meet a specific transient load requirement. Tuning is accomplished with
> > a single external resistor. They claim that by using TurboTrans one can
> > achieve a reduction in bulk output capacitance which leads to an
> > increase in ESR.
> >
> > Has anyone had any experience using this feature?
> >
> > The link below has more information.
> >
> > http://www.ti.com/corp/docs/landing/t2/index.htm
> >
> >
> >
> >
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> > On Behalf Of Bob McNamara
> > Sent: Wednesday, November 09, 2005 11:51 AM
> > To: matusov@xxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Re: ESR too low?
> >
> > [For anyone else trying to follow the link, it should be
> > http://focus.ti.com/docs/toolsw/folders/print/swift-sw.html]
> >
> > Thanks, I hadn't seen that software before. It's missing the ability to
> > optimize what I really care about as a user of the regulator - the
> > closed loop output impedance. I claim that if you optimize the closed
> > loop response, one consequence is that you'll have adequate phase
> > margin. On the other hand, optimizing the open loop response won't
> > guarantee me the best closed loop response.
> >
> > Bob McNamara
> > Broadcom Corp.
> >
> > --- Mikhail Matusov <matusov@xxxxxxxxxxxx> wrote:
> >
> > > > Now if only the vendors would supply such a tool...
> > >=20
> > > Have you seen the TI SWIFT Designer Software:
> > > http://focus.ti.com/docs/toolsw/folders/print/swift-sw.htm
> > >=20
> > >=20
> > >=20
> > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> > > Mikhail Matusov
> > > Hardware Design Engineer
> > > Square Peg Communications
> > > Tel.: +1 (613) 271-0044 ext.231
> > > Fax: +1 (613) 271-3007
> > > http://www.squarepeg.ca
> >
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