+5 to -5 charge pump thingie

J

John Larkin

Guest
I have +5 and need -5 at maybe 30 mA. A SOT-23 package would be nice.
We have a Maxim part in stock, but it's an SO-8 and, of course,
expensive.

Any favorites?

John
 
"John Larkin" <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote in
message news:5hh421dp9v27ob2qhjfqe3p03j991rrktm@4ax.com...
I have +5 and need -5 at maybe 30 mA. A SOT-23 package would be nice.
We have a Maxim part in stock, but it's an SO-8 and, of course,
expensive.

Any favorites?

John
Click to expand...
John, your better than that.
Take any digital signal in the system between 50KHz and 1MHz. Cap couple
it with a 100nF cap to the anode of a Shockley diode to gnd and cathode of
similar diode to the -4.65VDC output. Filter this output to gnd with 10uF.
But you knew all of this, why am I preaching to the choir? You must have
some other requirements.
Regards,
Harry
 
John Larkin <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote in
news:5hh421dp9v27ob2qhjfqe3p03j991rrktm@4ax.com:

I have +5 and need -5 at maybe 30 mA. A SOT-23 package would be nice.
We have a Maxim part in stock, but it's an SO-8 and, of course,
expensive.

Any favorites?

John
Click to expand...
LM2664
cheap as chips and works a treat
***NOT SHORT CIRCUIT PROTECTED*** (bitter experience)
M
 
On Sun, 27 Feb 2005 22:48:43 GMT, "Harry Dellamano"
<harryd@tdsystems.org> wrote:

"John Larkin" <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote in
message news:5hh421dp9v27ob2qhjfqe3p03j991rrktm@4ax.com...



I have +5 and need -5 at maybe 30 mA. A SOT-23 package would be nice.
We have a Maxim part in stock, but it's an SO-8 and, of course,
expensive.

Any favorites?

John

John, your better than that.
Take any digital signal in the system between 50KHz and 1MHz. Cap couple
it with a 100nF cap to the anode of a Shockley diode to gnd and cathode of
similar diode to the -4.65VDC output. Filter this output to gnd with 10uF.
But you knew all of this, why am I preaching to the choir? You must have
some other requirements.
Regards,
Harry
Click to expand...
The thing I'm doing is a little standalone optical-to-electrical
converter, in a few cubic inches of metal box, powered by a wall wart.
It's so simple it has no clocks or anything. I guess I could do a
schmitt-trigger oscillator and a charge pump, but that's a lot of
parts. I just need a negative rail for a couple of fast opamps.

I thought I'd ask the guys to see if anybody has a favorite part, and
just to make conversation.

John
 
In article <f7sUd.62262$uc.6123@trnddc04>, harryd@tdsystems.org says...
Take any digital signal in the system between 50KHz and 1MHz. Cap couple
it with a 100nF cap to the anode of a Shockley diode to gnd and cathode of
similar diode to the -4.65VDC output. Filter this output to gnd with 10uF.
But you knew all of this, why am I preaching to the choir? You must have
some other requirements.
Click to expand...
He said 30mA. Which means you would have to source and
sink >60mA (assuming 50% duty cycle). I doubt you'll get
that much current from "any digital signal in the system".
I've seen folks do things like parallel several buffers
or inverters to get drive for stunts like this. And then
there's the matter of the diode junction voltage loss.
He didn't say how close his -5 needed to be...
 
In article <3dm4219a0h15tmmkcl0oa21pnh2k3h1n37@4ax.com>,
John Larkin <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote:
[...]
The thing I'm doing is a little standalone optical-to-electrical
converter, in a few cubic inches of metal box, powered by a wall wart.
It's so simple it has no clocks or anything. I guess I could do a
schmitt-trigger oscillator and a charge pump, but that's a lot of
parts. I just need a negative rail for a couple of fast opamps.

I thought I'd ask the guys to see if anybody has a favorite part, and
just to make conversation.
Click to expand...
How about a 5V zener between the ground and the return of the wallwart?


--
--
kensmith@rahul.net forging knowledge
 
On Sun, 27 Feb 2005 14:16:06 -0800, John Larkin
<jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote:

I have +5 and need -5 at maybe 30 mA. A SOT-23 package would be nice.
We have a Maxim part in stock, but it's an SO-8 and, of course,
expensive.

Any favorites?

John
Click to expand...
I have +1.65V to +5.5V and need -1.5V

Device-level solution required

BUT, substrate is P-type, so the sneak paths get tricky ;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
 
On Sun, 27 Feb 2005 18:01:28 -0700, Jim Thompson
<thegreatone@example.com> wrote:

On Sun, 27 Feb 2005 14:16:06 -0800, John Larkin
jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote:




I have +5 and need -5 at maybe 30 mA. A SOT-23 package would be nice.
We have a Maxim part in stock, but it's an SO-8 and, of course,
expensive.

Any favorites?

John

I have +1.65V to +5.5V and need -1.5V

Device-level solution required

BUT, substrate is P-type, so the sneak paths get tricky ;-)

...Jim Thompson
Click to expand...
Somebody makes a something chip (not very specific, I admit) that has
a 3 GHz on-chip oscillator used to invert the Vcc for some reason.
Micrel or somebody with an M I think.

Isn't the classic bipolar process a p-type substrate? So if the
substrate is V-, diode isolation works for all the sigs on the chip,
but nothing can go negative without dire consequences.

Drams used to (still do?) pump the substrate negative.

John
 
On Mon, 28 Feb 2005 00:23:54 +0000 (UTC), kensmith@green.rahul.net
(Ken Smith) wrote:

In article <3dm4219a0h15tmmkcl0oa21pnh2k3h1n37@4ax.com>,
John Larkin <jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote:
[...]
The thing I'm doing is a little standalone optical-to-electrical
converter, in a few cubic inches of metal box, powered by a wall wart.
It's so simple it has no clocks or anything. I guess I could do a
schmitt-trigger oscillator and a charge pump, but that's a lot of
parts. I just need a negative rail for a couple of fast opamps.

I thought I'd ask the guys to see if anybody has a favorite part, and
just to make conversation.

How about a 5V zener between the ground and the return of the wallwart?
Click to expand...
I do want it to be possible to power a bunch of these from a grounded
+12 volt supply (if I can persuade anybody to buy a bunch of these) so
that's my preferred way to do this. Sounds like an LM2664 will invert
the +5 to give me enough to power the opamps.

John
 
On Sun, 27 Feb 2005 14:16:06 -0800, John Larkin wrote:

I have +5 and need -5 at maybe 30 mA. A SOT-23 package would be nice.
We have a Maxim part in stock, but it's an SO-8 and, of course,
expensive.

Any favorites?

John
Click to expand...
LTC1983-5 ?


Bob
 
On Mon, 28 Feb 2005 15:10:04 GMT, Bob Stephens
<stephensyomamadigital@earthlink.net> wrote:

On Sun, 27 Feb 2005 14:16:06 -0800, John Larkin wrote:

I have +5 and need -5 at maybe 30 mA. A SOT-23 package would be nice.
We have a Maxim part in stock, but it's an SO-8 and, of course,
expensive.

Any favorites?

John

LTC1983-5 ?
Click to expand...
$2.07 each. Yikes! I don't need the regulation, so the LM2664 looks
better at about $0.31 or something. Maxim and LTC are always way
expensive.

John
 
On Mon, 28 Feb 2005 08:23:18 -0800, John Larkin wrote:

On Mon, 28 Feb 2005 15:10:04 GMT, Bob Stephens
stephensyomamadigital@earthlink.net> wrote:

On Sun, 27 Feb 2005 14:16:06 -0800, John Larkin wrote:

I have +5 and need -5 at maybe 30 mA. A SOT-23 package would be nice.
We have a Maxim part in stock, but it's an SO-8 and, of course,
expensive.

Any favorites?

John

LTC1983-5 ?



$2.07 each. Yikes! I don't need the regulation, so the LM2664 looks
better at about $0.31 or something. Maxim and LTC are always way
expensive.

John
Click to expand...
Yeah,

My stuff is all low-volume military these days, so component cost isn't
 
On Mon, 28 Feb 2005 08:23:18 -0800, John Larkin wrote:

On Mon, 28 Feb 2005 15:10:04 GMT, Bob Stephens
stephensyomamadigital@earthlink.net> wrote:

On Sun, 27 Feb 2005 14:16:06 -0800, John Larkin wrote:

I have +5 and need -5 at maybe 30 mA. A SOT-23 package would be nice.
We have a Maxim part in stock, but it's an SO-8 and, of course,
expensive.

Any favorites?

John

LTC1983-5 ?



$2.07 each. Yikes! I don't need the regulation, so the LM2664 looks
better at about $0.31 or something. Maxim and LTC are always way
expensive.

John
Click to expand...
Yeah,

My stuff is all low-volume, military these days so component cost isn't
much of a concern.

Nice little part though.


Bob
 
In article <19vUd.82019$Yu.37749@fed1read01>,
Luhan Monat <see_signature@bottom.xyz> wrote:
[.. zener in return ..]
Bingo. I've done this, works great since op-amps are very noise-immune
from the power feeds.
Click to expand...

True for small values of "very". Most op-amps have a PSRR that decreases
with frequency. The neg rail PSRR is usually much worse than the plus
rail. A capacitor across the Zener will help a lot.

--
--
kensmith@rahul.net forging knowledge
 
In article <48r4211u3t7o9v4ipshavbkdcf86jkd246@4ax.com>,
Jim Thompson <thegreatone@example.com> wrote:
[...]
I have +1.65V to +5.5V and need -1.5V

Device-level solution required

BUT, substrate is P-type, so the sneak paths get tricky ;-)
Click to expand...
Is there an existing substrate pump? If so can you take some current from
it?

Is anything at ground?

-1.5V give or take how much?

I suggest a Pelter device between the chip and the heat sink.


--
--
kensmith@rahul.net forging knowledge
 
On Mon, 28 Feb 2005 18:18:08 -0700, Jim Thompson
<thegreatone@example.com> wrote:


Or just charge-pump off the flyback diode. I was doing that when you
were still a kid. Heck, *I* was still a kid.

John


I used that scheme to generate a nice regulated -5V in several of the
GenRad portable testers.

And I'm still a kid... I just LOOK old ;-)

...Jim Thompson
Click to expand...

You can also use little wire croquet-hoop thingies to secure a toroid
to the board, and then use them as secondaries, and rectify that.

John
 
Jim Thompson wrote:
On Mon, 28 Feb 2005 17:12:08 -0800, John Larkin
jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote:


On Mon, 28 Feb 2005 09:47:49 -0700, Jim Thompson
thegreatone@example.com> wrote:


On Mon, 28 Feb 2005 12:02:18 -0800, Jamie
jamie_5_not_valid_after_5_Please@charter.net> wrote:


John Larkin wrote:


On Mon, 28 Feb 2005 15:10:04 GMT, Bob Stephens
stephensyomamadigital@earthlink.net> wrote:



On Sun, 27 Feb 2005 14:16:06 -0800, John Larkin wrote:



I have +5 and need -5 at maybe 30 mA. A SOT-23 package would be nice.
We have a Maxim part in stock, but it's an SO-8 and, of course,
expensive.

Any favorites?

John

LTC1983-5 ?




$2.07 each. Yikes! I don't need the regulation, so the LM2664 looks
better at about $0.31 or something. Maxim and LTC are always way
expensive.

John


if the load is not that great have you throught about using a
5 V zener on the - side of the rectifier passing it through the diode
to your command of common - side ?
as long as you have an extra 5 volts to play with for + regulation this
should work well. it will give you a steady - 5 volts.
its a common pratice to do this in many integrated mini devices where
power usage is low.


If you already have a buck regulator in your system, you can steal
some negative power with this circuit on the S.E.D/Schematics Page of
my website...

OldStyleBuckSwitcherWithAddedNegativeOutput.pdf


Or just charge-pump off the flyback diode. I was doing that when you
were still a kid. Heck, *I* was still a kid.

John



I used that scheme to generate a nice regulated -5V in several of the
GenRad portable testers.

And I'm still a kid... I just LOOK old ;-)

...Jim Thompson
Click to expand...
Nice. I got to program a modern GenRad a few years back, it was fun.
Until one of the 0V relays froze - there were 32 in parallel. Fixing it
was fun though - I got the production staff to randomly call out
numbers, and I pulled those relays out. Got it the 5th time.

Cheers
Terry
 
On Sun, 27 Feb 2005 14:16:06 -0800, John Larkin wrote:



I have +5 and need -5 at maybe 30 mA. A SOT-23 package would be
nice.
We have a Maxim part in stock, but it's an SO-8 and, of course,
expensive.
Click to expand...
I once bought a 16K RAM pack for the ZX81,
and it used 4116 chips.
These need +12V and -5V, as well as the usual +5V.

The ZX81 only had +9V unregulated, and +5V.

I found they wired the +9V to the +12V rail (ugh!),
and used a 555 timer as an oscillator to drive a charge pump to make -5V.

I suspect they could have just used the CPU CLK (3.5 MHz) and a buffer gate
(or a pair of transistors) to drive a charge pump, and thus use smaller
caps.
 
In article <94jb21d985324s1k82r2pmnpcjkp7b8kr8@4ax.com>,
Jim Thompson <thegreatone@example.com> wrote:
[....]
Now for a dumb question: Why not use an N-channel?

--

Leakage when off. I'm dealing with pA.
Click to expand...
Bummer!

Use a MEMS relay

--
--
kensmith@rahul.net forging knowledge
 
In article <qdkb2198ernda9rmphrg17n693ecvhp3gj@4ax.com>,
Jim Thompson <thegreatone@example.com> wrote:
On Wed, 2 Mar 2005 14:38:53 +0000 (UTC), kensmith@green.rahul.net (Ken
Smith) wrote:

In article <94jb21d985324s1k82r2pmnpcjkp7b8kr8@4ax.com>,
Jim Thompson <thegreatone@example.com> wrote:
[....]
Now for a dumb question: Why not use an N-channel?

--

Leakage when off. I'm dealing with pA.

Bummer!

Use a MEMS relay

--

Hmmm! How much power? My total power budget is < 100uA.
Click to expand...
They can be electrostatically actuated so the static power is zero.

--
--
kensmith@rahul.net forging knowledge
 
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