Large capacitance varicaps, where are thee?

[miso]

miso wrote:
On 10/22/2012 2:22 PM, Joerg wrote:
Folks,

Looked at Digikey and some others. Where are those huge capacitance
varicaps? The ones with several hundred pF of range for AM radios. All
gone lalaland by now?

Even the ones I found in the 100pF range are either obsolete or not
recommended for new designs.

What I am trying to do: I need to control a switcher chip in frequency
because I've got a very resonant load to deal with. Unfortunately it
sets the frequency with a timing cap. I'll have to somehow vary that
between 750pF and 2000pF. Can also be digital but then with a
granularity of 5pF. The sawtooth voltage across it is 2.5Vpp.

Doing it with caps and a mux chip or two has its own challenges. The
ADG-series from AD is around 11pF per pin, otherwise their Rdson is too
high. Talking about the a rock and a hard spot here.

Oh, and cost is not very important. If a diode or two or three are
needed that cost $5 a pop that's ok.


There are plenty of hoarders that have those caps. I picked them up
years ago when I figured they would go extinct. They same goes for 10
turn pots of the panel variety with the dials on them. (Good old Mike
Quinn in San Leadro by the Oakland airport would save panels with those
pots and junk the rest of the product.] Most radios are synthesized
these days, so there is no market for those caps.


Yeah, I know but I was hoping there'd be at least one other market.
Seems like there ain't.


If you are not conflating sawtooth with triangle wave, then maybe you
could shunt some current from the osc pin, which would slow down the
frequency. Pick your external cap for the highest frequency needed, then
bleed with some DAC based circuit or even a resistive trimpot. The
10-turn PCB mounted resistors still exist.

The difficulty will be in the compliance of the current source used for
bleeding.


That won't be a problem but the chip immediately gets sea-sick when you
do anything DC to that pin.

Is this pin where you see the sawtooth? Seems to me with a high
impedance current source, you can steal the current. Now a triangle
waveform is a different case.

So you have tried a high impedance current source?

Yup. The chip then starts to misfire, big time, at least on the simulator.

None I ever designed would care.

BTW, you can always make a sawtooth generator go faster by inserting a
resistor in series with the cap. Basically it adds a step to the saw
tooth, getting you to the limit faster.

 

[Joerg]

On 10/22/2012 3:29 PM, Joerg wrote:
miso wrote:
On 10/22/2012 2:22 PM, Joerg wrote:
Folks,

Looked at Digikey and some others. Where are those huge capacitance
varicaps? The ones with several hundred pF of range for AM radios.
All
gone lalaland by now?

Even the ones I found in the 100pF range are either obsolete or not
recommended for new designs.

What I am trying to do: I need to control a switcher chip in
frequency
because I've got a very resonant load to deal with. Unfortunately it
sets the frequency with a timing cap. I'll have to somehow vary that
between 750pF and 2000pF. Can also be digital but then with a
granularity of 5pF. The sawtooth voltage across it is 2.5Vpp.

Doing it with caps and a mux chip or two has its own challenges. The
ADG-series from AD is around 11pF per pin, otherwise their Rdson
is too
high. Talking about the a rock and a hard spot here.

Oh, and cost is not very important. If a diode or two or three are
needed that cost $5 a pop that's ok.


There are plenty of hoarders that have those caps. I picked them up
years ago when I figured they would go extinct. They same goes for 10
turn pots of the panel variety with the dials on them. (Good old Mike
Quinn in San Leadro by the Oakland airport would save panels with
those
pots and junk the rest of the product.] Most radios are synthesized
these days, so there is no market for those caps.


Yeah, I know but I was hoping there'd be at least one other market.
Seems like there ain't.


If you are not conflating sawtooth with triangle wave, then maybe you
could shunt some current from the osc pin, which would slow down the
frequency. Pick your external cap for the highest frequency needed,
then
bleed with some DAC based circuit or even a resistive trimpot. The
10-turn PCB mounted resistors still exist.

The difficulty will be in the compliance of the current source used
for
bleeding.


That won't be a problem but the chip immediately gets sea-sick when you
do anything DC to that pin.


Is this pin where you see the sawtooth? Seems to me with a high
impedance current source, you can steal the current. Now a triangle
waveform is a different case.

So you have tried a high impedance current source?

Yup. The chip then starts to misfire, big time, at least on the
simulator.

None I ever designed would care.

Probably this one doesn't either, it's the simulator model that does. On
this design I absolutely need a simulator model because of the ugly
load. That shuts out most vendors.

BTW, you can always make a sawtooth generator go faster by inserting a
resistor in series with the cap. Basically it adds a step to the saw
tooth, getting you to the limit faster.

Can't do that here. The chip has internal comparators and certain things
need to happen at certain times on the ramp. So I'd rather keep that
ramp linear.

 

[Jamie]

miso wrote:

On 10/22/2012 3:29 PM, Joerg wrote:

miso wrote:

On 10/22/2012 2:22 PM, Joerg wrote:

Folks,

Looked at Digikey and some others. Where are those huge capacitance
varicaps? The ones with several hundred pF of range for AM radios.
All
gone lalaland by now?

Even the ones I found in the 100pF range are either obsolete or not
recommended for new designs.

What I am trying to do: I need to control a switcher chip in
frequency
because I've got a very resonant load to deal with. Unfortunately it
sets the frequency with a timing cap. I'll have to somehow vary that
between 750pF and 2000pF. Can also be digital but then with a
granularity of 5pF. The sawtooth voltage across it is 2.5Vpp.

Doing it with caps and a mux chip or two has its own challenges. The
ADG-series from AD is around 11pF per pin, otherwise their Rdson
is too
high. Talking about the a rock and a hard spot here.

Oh, and cost is not very important. If a diode or two or three are
needed that cost $5 a pop that's ok.


There are plenty of hoarders that have those caps. I picked them up
years ago when I figured they would go extinct. They same goes for 10
turn pots of the panel variety with the dials on them. (Good old Mike
Quinn in San Leadro by the Oakland airport would save panels with
those
pots and junk the rest of the product.] Most radios are synthesized
these days, so there is no market for those caps.


Yeah, I know but I was hoping there'd be at least one other market.
Seems like there ain't.



If you are not conflating sawtooth with triangle wave, then maybe you
could shunt some current from the osc pin, which would slow down the
frequency. Pick your external cap for the highest frequency needed,
then
bleed with some DAC based circuit or even a resistive trimpot. The
10-turn PCB mounted resistors still exist.

The difficulty will be in the compliance of the current source used
for
bleeding.


That won't be a problem but the chip immediately gets sea-sick when you
do anything DC to that pin.


Is this pin where you see the sawtooth? Seems to me with a high
impedance current source, you can steal the current. Now a triangle
waveform is a different case.

So you have tried a high impedance current source?


Yup. The chip then starts to misfire, big time, at least on the
simulator.

None I ever designed would care.

Probably this one doesn't either, it's the simulator model that does. On
this design I absolutely need a simulator model because of the ugly
load. That shuts out most vendors.

BTW, you can always make a sawtooth generator go faster by inserting a
resistor in series with the cap. Basically it adds a step to the saw
tooth, getting you to the limit faster.

Can't do that here. The chip has internal comparators and certain things
need to happen at certain times on the ramp. So I'd rather keep that
ramp linear.

Have you tried the op-amp trick to vary a fixed capacitor?

Depending on which way you need to shift it, lead of Lag will depend
if you do a invert or non-inverting input.

This is done commonly using a LM324 in many circuits.,









+/- rail supply

Lead circuit
+------------+
| |
REf in | |
+ | |\| | REF out
| +--+|-\ | ___
| | >-+---+----------+-|___|+---------+---------+
+----------+-|+/ | |
/| | --- Lead Cap
| +--------++ ---
| | + +
| | |\| | |
+ +--+|-\ + ___ |
.-. | >+-++-|___|++
| |<-+----+--+|+/
| | |/|
Lead Gain (D)'-'
|
===
GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)



This isn't exactly what you would use but is shows how you can bring in
a cap with the lead gain. This will insert the "Lead Cap" via the lead
gain and forward reference coming in.

Something to look at any way.
Jamie

 

[Joerg]

On 10/23/2012 12:40 PM, Joerg wrote:

miso wrote:

On 10/22/2012 3:29 PM, Joerg wrote:

miso wrote:

On 10/22/2012 2:22 PM, Joerg wrote:

Folks,

Looked at Digikey and some others. Where are those huge capacitance
varicaps? The ones with several hundred pF of range for AM radios.
All
gone lalaland by now?

Even the ones I found in the 100pF range are either obsolete or not
recommended for new designs.

What I am trying to do: I need to control a switcher chip in
frequency
because I've got a very resonant load to deal with.
Unfortunately it
sets the frequency with a timing cap. I'll have to somehow vary
that
between 750pF and 2000pF. Can also be digital but then with a
granularity of 5pF. The sawtooth voltage across it is 2.5Vpp.

Doing it with caps and a mux chip or two has its own challenges.
The
ADG-series from AD is around 11pF per pin, otherwise their Rdson
is too
high. Talking about the a rock and a hard spot here.

Oh, and cost is not very important. If a diode or two or three are
needed that cost $5 a pop that's ok.


There are plenty of hoarders that have those caps. I picked them up
years ago when I figured they would go extinct. They same goes
for 10
turn pots of the panel variety with the dials on them. (Good old
Mike
Quinn in San Leadro by the Oakland airport would save panels with
those
pots and junk the rest of the product.] Most radios are synthesized
these days, so there is no market for those caps.


Yeah, I know but I was hoping there'd be at least one other market.
Seems like there ain't.



If you are not conflating sawtooth with triangle wave, then maybe
you
could shunt some current from the osc pin, which would slow down the
frequency. Pick your external cap for the highest frequency needed,
then
bleed with some DAC based circuit or even a resistive trimpot. The
10-turn PCB mounted resistors still exist.

The difficulty will be in the compliance of the current source used
for
bleeding.


That won't be a problem but the chip immediately gets sea-sick
when you
do anything DC to that pin.


Is this pin where you see the sawtooth? Seems to me with a high
impedance current source, you can steal the current. Now a triangle
waveform is a different case.

So you have tried a high impedance current source?


Yup. The chip then starts to misfire, big time, at least on the
simulator.


None I ever designed would care.

Probably this one doesn't either, it's the simulator model that does. On
this design I absolutely need a simulator model because of the ugly
load. That shuts out most vendors.

BTW, you can always make a sawtooth generator go faster by inserting a
resistor in series with the cap. Basically it adds a step to the saw
tooth, getting you to the limit faster.

Can't do that here. The chip has internal comparators and certain things
need to happen at certain times on the ramp. So I'd rather keep that
ramp linear.

Have you tried the op-amp trick to vary a fixed capacitor?

Depending on which way you need to shift it, lead of Lag will depend
if you do a invert or non-inverting input.

This is done commonly using a LM324 in many circuits.,









+/- rail supply

Lead circuit
+------------+
| |
REf in | |
+ | |\| | REF out
| +--+|-\ | ___
| | >-+---+----------+-|___|+---------+---------+
+----------+-|+/ | |
/| | --- Lead Cap
| +--------++ ---
| | + +
| | |\| | |
+ +--+|-\ + ___ |
.-. | >+-++-|___|++
| |<-+----+--+|+/
| | |/|
Lead Gain (D)'-'
|
===
GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)



This isn't exactly what you would use but is shows how you can bring in
a cap with the lead gain. This will insert the "Lead Cap" via the lead
gain and forward reference coming in.

Something to look at any way.

Someone in the thread suggested something similar a while ago. A problem
is that the chip issues a reset pulse of about 50mA. But I've got it
running now, with current source.

 

[legg]

I receive all ON product notices (spec, process, material, source,
discontinuance, resurection etc etc etc) changes, and there's nothing
on SVC383.

Did you ask the ON recommended vendor - Rochester Electronics? They
also have no stock, but they shouldn't give you a phoney reason for
this. Digikey still lists their supplier for SVC389 as Sanyo
Semiconductor (USA), so their info for both parts may be dated. Did
you actually ask Digikey? Looks like the usual minimum purchase of a
reel, for items not recently stocked.

The issue is more likely a Sanyo-based supply chain one - strictly
sales related. I'd sniff around previously reliable Sanyo distribution
outlets (not excluding Digikey). SVC389 was also an RS Component line
item.

Correction on that:

ON issued a massive product discontinuance notice (PD16800) which
included Sony parts SVC233, SVC383 and SVC389 on 17 Jan of this year.

This was due to the catastrophic flooding in Thailand at that time.

US contact for existing inventory inquiries is listed as

Mark Gabrielle (email is [email protected])
602.244.3115
USA

RL

 

[Joerg]

Correction on that:

ON issued a massive product discontinuance notice (PD16800) which
included Sony parts SVC233, SVC383 and SVC389 on 17 Jan of this year.

This was due to the catastrophic flooding in Thailand at that time.

US contact for existing inventory inquiries is listed as

Mark Gabrielle (email is [email protected])
602.244.3115
USA

I doubt flooding is the real reason. There just is no market of
sufficient size for these anymore.

 

[legg]

I doubt flooding is the real reason. There just is no market of
sufficient size for these anymore.

They shut down the manufacturing facility.

"SANYO Semiconductor Thailand Co., Ltd. (SSTH)"

PD16800 covered over 200 discrete and integrated line items, half of
which had no recommended substitute, regardless of supplier ( other
sources' replacement products listed in this PD included Sanken,
Toshiba, NXP, Rohm, STMicro, Renesas, IR, Fairchild, MPS, Maxim and
ASAHIKASEI ).

The question is - Is there enough market to reopen or transfer the
product from the Sanyo subsidiary to an ON/Sanyo subsidiary.
Supposedly, they can get this info from inventory enquiries.....

RL

 

[legg]

Quite obviously they weren't worth the effort to restart the lines,
there or elsewhere.

It won't be obvious until regular distributors actually stop listing
the parts, but it makes use of them an unlikely choice for new
product development.

RL

 

[[email protected]]

It won't be obvious until regular distributors actually stop listing
the parts, but it makes use of them an unlikely choice for new
product development.

Huh? You wait until the distys run out before you stop designing with
obsolete parts? As soon as there is a whiff that a part is going
down, I'm outta here. We have one now that the supplier decided to
get out of the market until we told them why we picked their part.
They decided to stay in the market but there is a 75% chance that
we'll dump them anyway. Just can't take those chances.

 

[[email protected]]

It won't be obvious until regular distributors actually stop listing
the  parts, but it makes use of them an unlikely choice for new
product development.

RL

doesn't parts(that are actually used) on the way out tend to have some
exponential price increase?

Does tend to make sure that the ones who really need them get them,
not some one who just picked it because it was the first
they found

-Lasse

 

[[email protected]]

doesn't parts(that are actually used) on the way out tend to have some
exponential price increase?

After the production halts, sure. Those who didn't prepare pay the
scalpers. Unless you're so small that you buy only off the Internet
from DigiKey, and such, you do get discontinuance notices. Sometimes
they fall through the cracks (no system is perfect) but there are
warnings.

Does tend to make sure that the ones who really need them get them,
not some one who just picked it because it was the first
they found

Doesn't anyone look at the NOT FOR USE IN NEW DESIGNS warnings?

 

[legg]

After the production halts, sure. Those who didn't prepare pay the
scalpers. Unless you're so small that you buy only off the Internet
from DigiKey, and such, you do get discontinuance notices. Sometimes
they fall through the cracks (no system is perfect) but there are
warnings.


Doesn't anyone look at the NOT FOR USE IN NEW DESIGNS warnings?

Doesn't anyone require multiple sourcing any more?

My boms tend to require THREE inependently sourced parts, as
purchasing options. I relax at home, though, by building stuff from
unobtanium.

RL

 

[legg]

On Fri, 9 Nov 2012 17:06:44 -0800 (PST), "[email protected]"

Doesn't anyone look at the NOT FOR USE IN NEW DESIGNS warnings?

No warning on this one, just the PD.

RL

 

[[email protected]]

Doesn't anyone require multiple sourcing any more?

Good grief, how many parts *have* multiple sources. Many companies
are sourcing from multiple locations and even pay TSMC, for example,
as a hot standby. That doesn't stop them from discontinuing a part.

My boms tend to require THREE inependently sourced parts, as
purchasing options. I relax at home, though, by building stuff from
unobtanium.

You must do *really* boring shit.

 

[legg]

Good grief, how many parts *have* multiple sources. Many companies
are sourcing from multiple locations and even pay TSMC, for example,
as a hot standby. That doesn't stop them from discontinuing a part.


You must do *really* boring shit.

And you must spend a lot of time waitng for somebody else to do it for
you.

RL

 

[legg]

Things like uPs, FPGAs, ADCs, equalizers, PHYs, high-end analog chips,
DDSs, fast opamps, switching regulators, all sorts of high-end stuff
is sole-source.

....but occasionally not irreplaceable. If you don't even consider it,
you'll never know. If you do, it may be (it used to be....) worth the
effort.

How many posts does S.E.D. get, with just this issue?

If the 'end' is high, then so should be the engineering standards.
That's what you get paid for.

RL

 

[[email protected]]

And you must spend a lot of time waitng for somebody else to do it for
you.

You've obviously been bored to the point of being brain dead.

 

[[email protected]]

Things like uPs, FPGAs, ADCs, equalizers, PHYs, high-end analog chips,
DDSs, fast opamps, switching regulators, all sorts of high-end stuff
is sole-source.

....switching power supplies, most linear power supplies, audio
amplifiers, and just about everything else I've used in the past few
years outside of resistors and capacitors.

 

[[email protected]]

...but occasionally not irreplaceable. If you don't even consider it,
you'll never know. If you do, it may be (it used to be....) worth the
effort.

The software is worth more than the hardware. It's not worth the
effort anymore.

How many posts does S.E.D. get, with just this issue?

No one said you were alone doing boring shit.

If the 'end' is high, then so should be the engineering standards.
That's what you get paid for.

Red herring.