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Isolated variable resistor function?

J

Joerg

Jan 1, 1970
0
We don't always get our wishes.

But I want my wishes granted!

<stomp ... stomp ... stomp>

:)

Isn't the tolerance of the 4011 an issue?


It's exactly borderline but was only an example. I am pretty sure I can
find one that is less than 20%. If not we'll have to do an auto-cal on
start-up and the SW guys will throw their coffee mugs at me.
 
J

Joerg

Jan 1, 1970
0
Bill said:
You do need some - you did mention 5% linearity. And multipliers are
specified in a way that smears out the non-linearity over the whole of
the range, which you can rarely completely exploit.

If an RF mixer had 5% nonlinearity it would have a really lousy
intermodulation performance.
 
[email protected] wrote:

[email protected] wrote:

Jim Thompson wrote:
John Larkin wrote:
[snip]
Any chance you can PWM a resistor?

Would be nice but the part where the resulting signal goes into is
blazingly fast (has to be). So the PWM would cause an undesired modulation.

But it is an idea, maybe I can slow something down in there. And go in
with several meggeehoitzes. The uC we have would moan and groan though.
Please define "blazingly fast"?

In this case several MHz. In the world of switch mode power supplies
that counts as "blazingly fast" :)
Blazingly? Every switching supply I've designed in the last nine months has
had a Fsw > 2MHz. ;-)
But not da big ones.
Yeah, one is a "tiny" 400W boost. I cheated, though, and it's four-phase. ;-)
Most of the others are in the 15-20W class.

2MHz at 400W? That's pretty good. How did you get that to pass EMC and
be efficient?

I just got the first boards back a few weeks ago, so haven't, yet. ;-)
However, efficient should help. An extruded aluminum case should help, too
(the final product will be in a casting).

As I said, it's cheating but it's really four phases, each at 500kHz. It's an
advanced development project. One of the groundrules is that switching
regulators must be above 2MHz (AM band). This cheating was the only way I
found to get there. On another project, I have a couple of other smaller
2-phase buck regulators (2-phase, to get the power/efficiency up where its
needed).

If you run them at 500kHz that's a bog-standard switcher range. That's
not a 2MHz switcher. You won't be above the AM band with that unless you
have a super-precise balancing system in there.

Bog standard? Not really. Not at that power level. It's all in the tuning.
 
But I want my wishes granted!

<stomp ... stomp ... stomp>

:)




It's exactly borderline but was only an example. I am pretty sure I can
find one that is less than 20%. If not we'll have to do an auto-cal on
start-up and the SW guys will throw their coffee mugs at me.

As long as the processor is already there, tell them to stop whining. It's a
SMOP and takes no resources. Even the validation is a piece of cake.
 
F

Fred Bartoli

Jan 1, 1970
0
Joerg a écrit :
[email protected] wrote:

Jim Thompson wrote:
John Larkin wrote:
[snip]
Any chance you can PWM a resistor?

Would be nice but the part where the resulting signal goes into is
blazingly fast (has to be). So the PWM would cause an undesired modulation.

But it is an idea, maybe I can slow something down in there. And go in
with several meggeehoitzes. The uC we have would moan and groan though.
Please define "blazingly fast"?

In this case several MHz. In the world of switch mode power supplies
that counts as "blazingly fast" :)
Blazingly? Every switching supply I've designed in the last nine months has
had a Fsw > 2MHz. ;-)
But not da big ones.
Yeah, one is a "tiny" 400W boost. I cheated, though, and it's four-phase. ;-)
Most of the others are in the 15-20W class.

2MHz at 400W? That's pretty good. How did you get that to pass EMC and
be efficient?

He he, right now I have one (OK not boost) running 30W@27MHz.
circa 90% efficiency and passing EMC tests with flying colors (30dB
margin first pass :)
The power Xtor is SMD, under a buck.
The customer's designer is so p.....-..f (but he can't tell :) that he
insists on me reverting to an RF power Mosfet with all the implied mess,
which I won't...
 
J

Joerg

Jan 1, 1970
0
[email protected] wrote:

[email protected] wrote:

Jim Thompson wrote:
John Larkin wrote:
[snip]
Any chance you can PWM a resistor?

Would be nice but the part where the resulting signal goes into is
blazingly fast (has to be). So the PWM would cause an undesired modulation.

But it is an idea, maybe I can slow something down in there. And go in
with several meggeehoitzes. The uC we have would moan and groan though.
Please define "blazingly fast"?

In this case several MHz. In the world of switch mode power supplies
that counts as "blazingly fast" :)
Blazingly? Every switching supply I've designed in the last nine months has
had a Fsw > 2MHz. ;-)
But not da big ones.
Yeah, one is a "tiny" 400W boost. I cheated, though, and it's four-phase. ;-)
Most of the others are in the 15-20W class.
2MHz at 400W? That's pretty good. How did you get that to pass EMC and
be efficient?
I just got the first boards back a few weeks ago, so haven't, yet. ;-)
However, efficient should help. An extruded aluminum case should help, too
(the final product will be in a casting).

As I said, it's cheating but it's really four phases, each at 500kHz. It's an
advanced development project. One of the groundrules is that switching
regulators must be above 2MHz (AM band). This cheating was the only way I
found to get there. On another project, I have a couple of other smaller
2-phase buck regulators (2-phase, to get the power/efficiency up where its
needed).
If you run them at 500kHz that's a bog-standard switcher range. That's
not a 2MHz switcher. You won't be above the AM band with that unless you
have a super-precise balancing system in there.

Bog standard? Not really. Not at that power level.


At 400W? Not a big deal there to get to 500kHz if you keep switching
losses in check.

... It's all in the tuning.


For a ZVS, yes, definitely. But you can usually only tune that for the
upper ranges.
 
Joerg a écrit :
[email protected] wrote:

Jim Thompson wrote:
John Larkin wrote:
[snip]
Any chance you can PWM a resistor?

Would be nice but the part where the resulting signal goes into is
blazingly fast (has to be). So the PWM would cause an undesired modulation.

But it is an idea, maybe I can slow something down in there. And go in
with several meggeehoitzes. The uC we have would moan and groan though.
Please define "blazingly fast"?

In this case several MHz. In the world of switch mode power supplies
that counts as "blazingly fast" :)
Blazingly? Every switching supply I've designed in the last nine months has
had a Fsw > 2MHz. ;-)
But not da big ones.
Yeah, one is a "tiny" 400W boost. I cheated, though, and it's four-phase. ;-)
Most of the others are in the 15-20W class.

2MHz at 400W? That's pretty good. How did you get that to pass EMC and
be efficient?

He he, right now I have one (OK not boost) running 30W@27MHz.
circa 90% efficiency and passing EMC tests with flying colors (30dB
margin first pass :)
The power Xtor is SMD, under a buck.

Sure, one of the other engineers wants to go to a TO-220 but that scares the
crap outta me and the cost of mounting eight of them isn't trivial either. The
part I'm using (TI) is pretty good and well under a buck (at half-million ;-).
 
J

Jon Kirwan

Jan 1, 1970
0
Amazing! Maybe I should use a F5 series some day.

I ordered a couple of samples, just 'cause. I didn't know
about Timer D until a few days ago, anyway. Curious about
playing with it. I have a need to create tiny "runt" pulses
in a signal and this might be usefully fast enough.

I need to check pricing. A fast PWM makes some things cheaper
(such as living with an RC filter with sloppy 20db/decade
rolloff) but if it costs a lot more then you lose the price
benefit. There are a lot of ways of doing things.

Jon
 
J

Joerg

Jan 1, 1970
0
Fred said:
Joerg a écrit :
[email protected] wrote:
Jim Thompson wrote:
John Larkin wrote:
[snip]
Any chance you can PWM a resistor?

Would be nice but the part where the resulting signal goes into is
blazingly fast (has to be). So the PWM would cause an undesired
modulation.

But it is an idea, maybe I can slow something down in there. And
go in
with several meggeehoitzes. The uC we have would moan and groan
though.
Please define "blazingly fast"?

In this case several MHz. In the world of switch mode power supplies
that counts as "blazingly fast" :)
Blazingly? Every switching supply I've designed in the last nine
months has
had a Fsw > 2MHz. ;-)
But not da big ones.
Yeah, one is a "tiny" 400W boost. I cheated, though, and it's
four-phase. ;-)
Most of the others are in the 15-20W class.

2MHz at 400W? That's pretty good. How did you get that to pass EMC and
be efficient?

He he, right now I have one (OK not boost) running 30W@27MHz.
circa 90% efficiency and passing EMC tests with flying colors (30dB
margin first pass :)
The power Xtor is SMD, under a buck.


Running on the loophole frequency of 27.12MHz? It's been a long time but
IIRC my highest resonant one was "only" 13.56MHz and on those
frequencies it is very easy to pass EMC.

The customer's designer is so p.....-..f (but he can't tell :) that he
insists on me reverting to an RF power Mosfet with all the implied mess,
which I won't...

I wouldn't either, those RF FETs cost a ton and many don't come with
SPICE models. Which is a big no-no for me.
 
J

Joerg

Jan 1, 1970
0
Jim said:
Jim said:
John Larkin wrote:
[snip]
Any chance you can PWM a resistor?

Would be nice but the part where the resulting signal goes into is
blazingly fast (has to be). So the PWM would cause an undesired modulation.

But it is an idea, maybe I can slow something down in there. And go in
with several meggeehoitzes. The uC we have would moan and groan though.
Please define "blazingly fast"?
In this case several MHz. In the world of switch mode power supplies
that counts as "blazingly fast" :)

Is current flow in the resistor unidirectional... doesn't pass thru
zero?

Yes, unidirectional. Goes to zero at times but never crosses onto
negative turf.
 
J

Joerg

Jan 1, 1970
0
[...]
It's exactly borderline but was only an example. I am pretty sure I can
find one that is less than 20%. If not we'll have to do an auto-cal on
start-up and the SW guys will throw their coffee mugs at me.

As long as the processor is already there, tell them to stop whining. It's a
SMOP and takes no resources. Even the validation is a piece of cake.

Wot's a SMOP?
 
J

Joerg

Jan 1, 1970
0
Tim said:

[...]
Actually single quadrant is ok and one side of it can be grounded. Cost
is a factor but not like in most of my other design. Meaning a buck is
acceptable but two bucks would be a stretch.

If it's for a voltage divider, what about a multiplying DAC? You'd still
need the two wires to talk to it, but you could make whatever $$ vs.
precision tradeoff your heart desired.

I thought about a DAC of the old kind, with the switched and accessible
R2R array in there. In essence that's almost the same as using a digital
potmeter except it has better granularity. 6 bits would be plenty here
though and digipots come in SOT23-5 and sometimes smaller.
 
F

Fred Bartoli

Jan 1, 1970
0
Joerg a écrit :
Fred said:
Joerg a écrit :
[email protected] wrote:
[email protected] wrote:
Jim Thompson wrote:
John Larkin wrote:
[snip]
Any chance you can PWM a resistor?

Would be nice but the part where the resulting signal goes into is
blazingly fast (has to be). So the PWM would cause an undesired
modulation.

But it is an idea, maybe I can slow something down in there. And
go in
with several meggeehoitzes. The uC we have would moan and groan
though.
Please define "blazingly fast"?

In this case several MHz. In the world of switch mode power supplies
that counts as "blazingly fast" :)
Blazingly? Every switching supply I've designed in the last nine
months has
had a Fsw > 2MHz. ;-)
But not da big ones.
Yeah, one is a "tiny" 400W boost. I cheated, though, and it's
four-phase. ;-)
Most of the others are in the 15-20W class.

2MHz at 400W? That's pretty good. How did you get that to pass EMC and
be efficient?
He he, right now I have one (OK not boost) running 30W@27MHz.
circa 90% efficiency and passing EMC tests with flying colors (30dB
margin first pass :)
The power Xtor is SMD, under a buck.


Running on the loophole frequency of 27.12MHz? It's been a long time but
IIRC my highest resonant one was "only" 13.56MHz and on those
frequencies it is very easy to pass EMC.

Nope... No loophole there. It has to pass A class levels
I wouldn't either, those RF FETs cost a ton and many don't come with
SPICE models. Which is a big no-no for me.

Well, at these frequencies others spice models, mostly "designed" for
SMPS are such a joke...

I had to do fire up the VNA, curve tracer,... and run my own one.

The hardest part was to find suitable air inductor makers in small
quantities. I've seen quite a bit of horror stories there.
 
J

Jon Kirwan

Jan 1, 1970
0
If that's like what they were doing on their 28F3xx DSP parts several
years ago, it's a regular ol' PWM followed by a variable time delay.

Which isn't to say that it's not a good idea, or an eminently workable
one.

It seems likely to be a PLL multiplier, given my ignorance.
As in what Atmel does for some parts, too. It only supports
two integers (8 and 16) and that's pretty easy to do, as I
understand things. (I think TI acquired Nat Semi (2011) and
if so they got access to a VCO/PLL ranging up to 4GHz, too.
Might not be just a coincidence here.) But you'd know better
than I.

Jon
 
J

Joerg

Jan 1, 1970
0
Fred said:
Joerg a écrit :
Fred said:
Joerg a écrit :
[email protected] wrote:
[email protected] wrote:
Jim Thompson wrote:
On Sat, 25 Aug 2012 12:05:15 -0700, Joerg
<[email protected]>
wrote:

John Larkin wrote:
[snip]
Any chance you can PWM a resistor?

Would be nice but the part where the resulting signal goes
into is
blazingly fast (has to be). So the PWM would cause an undesired
modulation.

But it is an idea, maybe I can slow something down in there. And
go in
with several meggeehoitzes. The uC we have would moan and groan
though.
Please define "blazingly fast"?

In this case several MHz. In the world of switch mode power
supplies
that counts as "blazingly fast" :)
Blazingly? Every switching supply I've designed in the last nine
months has
had a Fsw > 2MHz. ;-)
But not da big ones.
Yeah, one is a "tiny" 400W boost. I cheated, though, and it's
four-phase. ;-)
Most of the others are in the 15-20W class.

2MHz at 400W? That's pretty good. How did you get that to pass EMC and
be efficient?

He he, right now I have one (OK not boost) running 30W@27MHz.
circa 90% efficiency and passing EMC tests with flying colors (30dB
margin first pass :)
The power Xtor is SMD, under a buck.


Running on the loophole frequency of 27.12MHz? It's been a long time but
IIRC my highest resonant one was "only" 13.56MHz and on those
frequencies it is very easy to pass EMC.

Nope... No loophole there. It has to pass A class levels

My stuff always has to pass class B or something much more strict (like
RTCA/DO-160).

At 27.12MHz (civilian) you can often use a loophole.

Well, at these frequencies others spice models, mostly "designed" for
SMPS are such a joke...

I've had pretty good results so far. Knocking on wood.

I had to do fire up the VNA, curve tracer,... and run my own one.

That's one reason the old HP3577 is still here :)

If it just wasn't so noisy with it's fan.
The hardest part was to find suitable air inductor makers in small
quantities. I've seen quite a bit of horror stories there.

Have you talked to Gowanda?
 
J

Joerg

Jan 1, 1970
0
Phil said:
Joerg said:
[...]
Wot's a SMOP?

Simple Matter of Programming. From the IBMJARG file:

SMOP
n. Something quite possible, but requiring unavailable resources to
achieve.
"Why isn't that function available in the program?--It's just a Simple
Matter Of Programming". (The implication being that, given a few
person-centuries, all things are possible.)
Also _SMOUP_ (smoop), a Simple Matter Of Micro-Programming (if
hand-written, using a Greek mu).

Thanks. I learn something new every day :)

The "takes no resources" part is not true. Every ever so tiny project
needs to be managed, reviewed, documented, regression-tested,
ECO-released, and on and on. Changing the thread diameter of a screw can
easily cause many manhours of extra work.
 
J

Joerg

Jan 1, 1970
0
Phil said:
Joerg said:
Phil said:
Joerg wrote:
[email protected] wrote: [...]

As long as the processor is already there, tell them to stop whining. It's a
SMOP and takes no resources. Even the validation is a piece of cake.

Wot's a SMOP?

--
Regards, Joerg

http://www.analogconsultants.com/
Simple Matter of Programming. From the IBMJARG file:

SMOP
n. Something quite possible, but requiring unavailable resources to
achieve.
"Why isn't that function available in the program?--It's just a Simple
Matter Of Programming". (The implication being that, given a few
person-centuries, all things are possible.)
Also _SMOUP_ (smoop), a Simple Matter Of Micro-Programming (if
hand-written, using a Greek mu).
Thanks. I learn something new every day :)

The "takes no resources" part is not true. Every ever so tiny project
needs to be managed, reviewed, documented, regression-tested,
ECO-released, and on and on. Changing the thread diameter of a screw can
easily cause many manhours of extra work.

"Takes unavailable resources" means "takes resources that are not
available", i.e. you and IBMJARG are in violent agreement.

I meant what Keith wrote :)

As for unavailable resources, our drill sergeant had a solution for
that. Sometimes he hollered "The day has 24 hours and if that's not
enough there's still the night!"
 
J

Jon Kirwan

Jan 1, 1970
0
Not necessarily. I know what they did on one part years ago, but I
haven't looked recently -- maybe they have figured out a clean way to do
this that involves an oscillator running at 256MHz. It'd certainly solve
a bunch of problems with variable time delays, even as it introduced a
bunch of other ones.

Well, as I pointed to before, take a look at Figure 19-2 in
the Family User's Guide, found following from here:

http://www.ti.com/product/msp430f5172&DCMP=msp430&HQS=430timer

It is behaviorally diagrammed as a fast clock generator
followed by your basic /1 /2 /4 /8 divider. It picks off of
the IDEX divider against the regular clock sources, so on
that level it looks like a normal multiplier. It includes an
"in-lock" bit, TDHLKIFG, to inform you when lock is achieved.

It also runs completely free. No lock, no care about another
oscillator, at all. So all that makes me think they actually
have a fast internal DCO of some kind, but where it can
optionally be locked to a lower speed crystal source.

Some words may relate to what you were saying, Tim. I see
this:

In regulated mode, the high-resolution generator
produces 8 or 16 equidistant events per timer
input clock cycle. Regulation is enabled by setting
the high-resolution calibration enable bit TDHREGEN.
The high-resolution generator tracks changes of the
timer input clock after locking to the timer input
clock frequency. Locking is indicated by setting the
lock interrupt flag TDHLKIFG. As long as the high-
resolution generator is not locked, the interrupt
flag TDHUNLKIFG is set.

If the timer input clock is out of the frequency
range of the high-resolution generator, then the
fail-high interrupt flag (TDHFHIFG) or the fail-
low interrupt flag (TDHFLIFG) is set.

If the TDHREGEN bit is cleared, the continuous
regulation is stopped and the high-resolution
frequency enters free-running mode. The latest
settings are kept.

There is no datasheet yet and so I can't look at related
specs that might help elucidate any better. I assumed that
they folded in Nat Semi technology (they are doing this with
their work on FRAM, too) to reach 256MHz in their process.

It's a little odd on the MSP430, as it goes upstream of their
"extremely low power" selling point (valid and well-made.) If
they were doing this and keeping most of the high clock rate
stuff tightly contained in small region of the die, perhaps
it would still be 'congruent.' But they use it to drive an
entire timer counter and this also means fast compare logic,
as well. So it starts to look like more die space is involved
than less and I have to imagine current draw will be
unusually high then.

Still, it is another selling point corner, I suppose.

Jon
 
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