Rail Splitting Chips...

[Ricky]

I read some of the discussion on \"rail splitting\" and it occurred to me that there should be a market for these devices. I am working on a design that will run op amps from a single rail and I need a 6V level, that can both source and sink current. The board is really tight. Presently it is using zeners to set a level (one for each channel to reduce crosstalk), but I was looking at using an LDO, with a resistor to sink current.

But the new design is going to have some higher current requirements, and this would be a consistent load using the resistor. The obvious solution would be to set a reference point using resistors, and an op amp to provide the drive. The reference point doesn\'t need to be highly accurate or stable. A cap would reduce noise.

I\'m wondering if there are chips available that already do this providing say, 30 mA of drive/sink?

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

[boB]

On Thu, 9 Mar 2023 12:18:25 -0800 (PST), Ricky
<gnuarm.deletethisbit@gmail.com> wrote:

I read some of the discussion on \"rail splitting\" and it occurred to me that there should be a market for these devices. I am working on a design that will run op amps from a single rail and I need a 6V level, that can both source and sink current. The board is really tight. Presently it is using zeners to set a level (one for each channel to reduce crosstalk), but I was looking at using an LDO, with a resistor to sink current.

But the new design is going to have some higher current requirements, and this would be a consistent load using the resistor. The obvious solution would be to set a reference point using resistors, and an op amp to provide the drive. The reference point doesn\'t need to be highly accurate or stable. A cap would reduce noise.

I\'m wondering if there are chips available that already do this providing say, 30 mA of drive/sink?

You would think there would be one of these but I still take 2 equal
value resistors and feed into a unity gain follower op-amp to supply
half-Vcc. Usually one half of a dual op-amp.

This would be a good use for a SOT-23 package....

But since it is just for bias, could use a SOT-23 NPN follower biased
up Vcc/2 + 0.65V or so.

boB

 

[Phil Hobbs]

On 2023-03-09 15:50, boB wrote:

On Thu, 9 Mar 2023 12:18:25 -0800 (PST), Ricky
gnuarm.deletethisbit@gmail.com> wrote:

I read some of the discussion on \"rail splitting\" and it occurred to me that there should be a market for these devices. I am working on a design that will run op amps from a single rail and I need a 6V level, that can both source and sink current. The board is really tight. Presently it is using zeners to set a level (one for each channel to reduce crosstalk), but I was looking at using an LDO, with a resistor to sink current.

But the new design is going to have some higher current requirements, and this would be a consistent load using the resistor. The obvious solution would be to set a reference point using resistors, and an op amp to provide the drive. The reference point doesn\'t need to be highly accurate or stable. A cap would reduce noise.

I\'m wondering if there are chips available that already do this providing say, 30 mA of drive/sink?


You would think there would be one of these but I still take 2 equal
value resistors and feed into a unity gain follower op-amp to supply
half-Vcc. Usually one half of a dual op-amp.

This would be a good use for a SOT-23 package....

But since it is just for bias, could use a SOT-23 NPN follower biased
up Vcc/2 + 0.65V or so.

boB

TI sells a dedicated rail splitter chip, the TLE2426. It costs more
than a TCA0372 and doesn\'t have nearly the oomph. Plus the TCA0372 is a
dual, so you can use the other half to do useful work too.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Arie de Muijnck]

On 2023-03-09 21:18, Ricky wrote:

I read some of the discussion on \"rail splitting\" and it occurred to me that there should be a market for these devices. I am working on a design that will run op amps from a single rail and I need a 6V level, that can both source and sink current. The board is really tight. Presently it is using zeners to set a level (one for each channel to reduce crosstalk), but I was looking at using an LDO, with a resistor to sink current.

But the new design is going to have some higher current requirements, and this would be a consistent load using the resistor. The obvious solution would be to set a reference point using resistors, and an op amp to provide the drive. The reference point doesn\'t need to be highly accurate or stable. A cap would reduce noise.

I\'m wondering if there are chips available that already do this providing say, 30 mA of drive/sink?

I\'ve used TI DDR Vref drivers that create the half voltage for the DDR termination at high amps, see e.g. https://www.ti.com/lit/an/slua886a/slua886a.pdf.
However, they are mainly for low voltages, only the TPS53317A https://www.ti.com/lit/ds/slusc63a/slusc63a.pdf will handle 6V input, but not 12V.
Maybe there are others?

Arie

 

[John Larkin]

On Thu, 9 Mar 2023 15:55:53 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-03-09 15:50, boB wrote:
On Thu, 9 Mar 2023 12:18:25 -0800 (PST), Ricky
gnuarm.deletethisbit@gmail.com> wrote:

I read some of the discussion on \"rail splitting\" and it occurred to me that there should be a market for these devices. I am working on a design that will run op amps from a single rail and I need a 6V level, that can both source and sink current. The board is really tight. Presently it is using zeners to set a level (one for each channel to reduce crosstalk), but I was looking at using an LDO, with a resistor to sink current.

But the new design is going to have some higher current requirements, and this would be a consistent load using the resistor. The obvious solution would be to set a reference point using resistors, and an op amp to provide the drive. The reference point doesn\'t need to be highly accurate or stable. A cap would reduce noise.

I\'m wondering if there are chips available that already do this providing say, 30 mA of drive/sink?


You would think there would be one of these but I still take 2 equal
value resistors and feed into a unity gain follower op-amp to supply
half-Vcc. Usually one half of a dual op-amp.

This would be a good use for a SOT-23 package....

But since it is just for bias, could use a SOT-23 NPN follower biased
up Vcc/2 + 0.65V or so.

boB


TI sells a dedicated rail splitter chip, the TLE2426. It costs more
than a TCA0372 and doesn\'t have nearly the oomph. Plus the TCA0372 is a
dual, so you can use the other half to do useful work too.

Cheers

Phil Hobbs

The TCA0372 data sheet only mentions +-15 supplies, but it actually
works at 5 volts between rails.

There\'s no power pad, but lots of V- pins on the 16-pin versions.

 

[bitrex]

On 3/9/2023 3:18 PM, Ricky wrote:

I read some of the discussion on \"rail splitting\" and it occurred to me that there should be a market for these devices. I am working on a design that will run op amps from a single rail and I need a 6V level, that can both source and sink current. The board is really tight. Presently it is using zeners to set a level (one for each channel to reduce crosstalk), but I was looking at using an LDO, with a resistor to sink current.

But the new design is going to have some higher current requirements, and this would be a consistent load using the resistor. The obvious solution would be to set a reference point using resistors, and an op amp to provide the drive. The reference point doesn\'t need to be highly accurate or stable. A cap would reduce noise.

I\'m wondering if there are chips available that already do this providing say, 30 mA of drive/sink?

Would an LM386 in VSSOP-8 be too old-fashioned? It will naturally bias
up to half the supply +/- not highly accurate or stable.

 

[Ricky]

On Thursday, March 9, 2023 at 3:51:02 PM UTC-5, boB wrote:

On Thu, 9 Mar 2023 12:18:25 -0800 (PST), Ricky
gnuarm.del...@gmail.com> wrote:

I read some of the discussion on \"rail splitting\" and it occurred to me that there should be a market for these devices. I am working on a design that will run op amps from a single rail and I need a 6V level, that can both source and sink current. The board is really tight. Presently it is using zeners to set a level (one for each channel to reduce crosstalk), but I was looking at using an LDO, with a resistor to sink current.

But the new design is going to have some higher current requirements, and this would be a consistent load using the resistor. The obvious solution would be to set a reference point using resistors, and an op amp to provide the drive. The reference point doesn\'t need to be highly accurate or stable. A cap would reduce noise.

I\'m wondering if there are chips available that already do this providing say, 30 mA of drive/sink?
You would think there would be one of these but I still take 2 equal
value resistors and feed into a unity gain follower op-amp to supply
half-Vcc. Usually one half of a dual op-amp.

This would be a good use for a SOT-23 package....

But since it is just for bias, could use a SOT-23 NPN follower biased
up Vcc/2 + 0.65V or so.

The NPN follower would require the same resistor I would use with an LDO. So that\'s not much better, drawing the current all the time. In fact, when the load is pulling up, both the resistor and the LDO draw current!

The op amp is reasonable, but it\'s bigger than what is possible. It just seems like something aught to be available. A zener is not bad, but a three terminal device is ideal. Power, ground and output, no passives. SC-70 package or smaller. This board is going to be seriously tight.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

 

[Lasse Langwadt Christensen]

fredag den 10. marts 2023 kl. 00.12.39 UTC+1 skrev Ricky:

On Thursday, March 9, 2023 at 3:51:02 PM UTC-5, boB wrote:
On Thu, 9 Mar 2023 12:18:25 -0800 (PST), Ricky
gnuarm.del...@gmail.com> wrote:

I read some of the discussion on \"rail splitting\" and it occurred to me that there should be a market for these devices. I am working on a design that will run op amps from a single rail and I need a 6V level, that can both source and sink current. The board is really tight. Presently it is using zeners to set a level (one for each channel to reduce crosstalk), but I was looking at using an LDO, with a resistor to sink current.

But the new design is going to have some higher current requirements, and this would be a consistent load using the resistor. The obvious solution would be to set a reference point using resistors, and an op amp to provide the drive. The reference point doesn\'t need to be highly accurate or stable. A cap would reduce noise.

I\'m wondering if there are chips available that already do this providing say, 30 mA of drive/sink?
You would think there would be one of these but I still take 2 equal
value resistors and feed into a unity gain follower op-amp to supply
half-Vcc. Usually one half of a dual op-amp.

This would be a good use for a SOT-23 package....

But since it is just for bias, could use a SOT-23 NPN follower biased
up Vcc/2 + 0.65V or so.
The NPN follower would require the same resistor I would use with an LDO. So that\'s not much better, drawing the current all the time. In fact, when the load is pulling up, both the resistor and the LDO draw current!

npn+pnp follower, https://imgur.com/NhlLGGc

 

[Ricky]

On Thursday, March 9, 2023 at 3:56:22 PM UTC-5, Phil Hobbs wrote:

On 2023-03-09 15:50, boB wrote:
On Thu, 9 Mar 2023 12:18:25 -0800 (PST), Ricky
gnuarm.del...@gmail.com> wrote:

I read some of the discussion on \"rail splitting\" and it occurred to me that there should be a market for these devices. I am working on a design that will run op amps from a single rail and I need a 6V level, that can both source and sink current. The board is really tight. Presently it is using zeners to set a level (one for each channel to reduce crosstalk), but I was looking at using an LDO, with a resistor to sink current.

But the new design is going to have some higher current requirements, and this would be a consistent load using the resistor. The obvious solution would be to set a reference point using resistors, and an op amp to provide the drive. The reference point doesn\'t need to be highly accurate or stable. A cap would reduce noise.

I\'m wondering if there are chips available that already do this providing say, 30 mA of drive/sink?


You would think there would be one of these but I still take 2 equal
value resistors and feed into a unity gain follower op-amp to supply
half-Vcc. Usually one half of a dual op-amp.

This would be a good use for a SOT-23 package....

But since it is just for bias, could use a SOT-23 NPN follower biased
up Vcc/2 + 0.65V or so.

boB

TI sells a dedicated rail splitter chip, the TLE2426. It costs more
than a TCA0372 and doesn\'t have nearly the oomph. Plus the TCA0372 is a
dual, so you can use the other half to do useful work too.

Both parts have the same problem, far too large. I barely have room for a pair of zeners. A SOT23 would suit, but better something smaller.

If I had a use for the op amp, I would have a spare op amp in the dual packages I\'m using.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

 

[boB]

On Thu, 09 Mar 2023 13:11:22 -0800, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

On Thu, 9 Mar 2023 15:55:53 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-03-09 15:50, boB wrote:
On Thu, 9 Mar 2023 12:18:25 -0800 (PST), Ricky
gnuarm.deletethisbit@gmail.com> wrote:

I read some of the discussion on \"rail splitting\" and it occurred to me that there should be a market for these devices. I am working on a design that will run op amps from a single rail and I need a 6V level, that can both source and sink current. The board is really tight. Presently it is using zeners to set a level (one for each channel to reduce crosstalk), but I was looking at using an LDO, with a resistor to sink current.

But the new design is going to have some higher current requirements, and this would be a consistent load using the resistor. The obvious solution would be to set a reference point using resistors, and an op amp to provide the drive. The reference point doesn\'t need to be highly accurate or stable. A cap would reduce noise.

I\'m wondering if there are chips available that already do this providing say, 30 mA of drive/sink?


You would think there would be one of these but I still take 2 equal
value resistors and feed into a unity gain follower op-amp to supply
half-Vcc. Usually one half of a dual op-amp.

This would be a good use for a SOT-23 package....

But since it is just for bias, could use a SOT-23 NPN follower biased
up Vcc/2 + 0.65V or so.

boB


TI sells a dedicated rail splitter chip, the TLE2426. It costs more
than a TCA0372 and doesn\'t have nearly the oomph. Plus the TCA0372 is a
dual, so you can use the other half to do useful work too.

Cheers

Phil Hobbs

The TCA0372 data sheet only mentions +-15 supplies, but it actually
works at 5 volts between rails.

There\'s no power pad, but lots of V- pins on the 16-pin versions.

Interesting ! I would have possibly used one if it could split 3.3V
for LV applications.

But, that might be a single-sourced part ? Haven\'t looked at the
price.

boB

 

[John Larkin]

On Thu, 09 Mar 2023 16:40:25 -0700, boB <boB@K7IQ.com> wrote:

On Thu, 09 Mar 2023 13:11:22 -0800, John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote:

On Thu, 9 Mar 2023 15:55:53 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-03-09 15:50, boB wrote:
On Thu, 9 Mar 2023 12:18:25 -0800 (PST), Ricky
gnuarm.deletethisbit@gmail.com> wrote:

I read some of the discussion on \"rail splitting\" and it occurred to me that there should be a market for these devices. I am working on a design that will run op amps from a single rail and I need a 6V level, that can both source and sink current. The board is really tight. Presently it is using zeners to set a level (one for each channel to reduce crosstalk), but I was looking at using an LDO, with a resistor to sink current.

But the new design is going to have some higher current requirements, and this would be a consistent load using the resistor. The obvious solution would be to set a reference point using resistors, and an op amp to provide the drive. The reference point doesn\'t need to be highly accurate or stable. A cap would reduce noise.

I\'m wondering if there are chips available that already do this providing say, 30 mA of drive/sink?


You would think there would be one of these but I still take 2 equal
value resistors and feed into a unity gain follower op-amp to supply
half-Vcc. Usually one half of a dual op-amp.

This would be a good use for a SOT-23 package....

But since it is just for bias, could use a SOT-23 NPN follower biased
up Vcc/2 + 0.65V or so.

boB


TI sells a dedicated rail splitter chip, the TLE2426. It costs more
than a TCA0372 and doesn\'t have nearly the oomph. Plus the TCA0372 is a
dual, so you can use the other half to do useful work too.

Cheers

Phil Hobbs

The TCA0372 data sheet only mentions +-15 supplies, but it actually
works at 5 volts between rails.

There\'s no power pad, but lots of V- pins on the 16-pin versions.


Interesting ! I would have possibly used one if it could split 3.3V
for LV applications.

But, that might be a single-sourced part ? Haven\'t looked at the
price.

boB

We pay 44 cents.

 

[Ricky]

On Thursday, March 9, 2023 at 4:45:26 PM UTC-5, bitrex wrote:

On 3/9/2023 3:18 PM, Ricky wrote:
I read some of the discussion on \"rail splitting\" and it occurred to me that there should be a market for these devices. I am working on a design that will run op amps from a single rail and I need a 6V level, that can both source and sink current. The board is really tight. Presently it is using zeners to set a level (one for each channel to reduce crosstalk), but I was looking at using an LDO, with a resistor to sink current.

But the new design is going to have some higher current requirements, and this would be a consistent load using the resistor. The obvious solution would be to set a reference point using resistors, and an op amp to provide the drive. The reference point doesn\'t need to be highly accurate or stable. A cap would reduce noise.

I\'m wondering if there are chips available that already do this providing say, 30 mA of drive/sink?

Would an LM386 in VSSOP-8 be too old-fashioned? It will naturally bias
up to half the supply +/- not highly accurate or stable.

I don\'t care about \"old fashioned\". Everything we design is old fashioned, other than the new bits that we have to come up with.

I just want it to be very small. I can get an op amp in a small package, so that\'s likely what I\'ll do. But we\'ll see what turns up. Thanks.

--

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209

 

[Ricky]

On Thursday, March 9, 2023 at 6:18:06 PM UTC-5, Lasse Langwadt Christensen wrote:

fredag den 10. marts 2023 kl. 00.12.39 UTC+1 skrev Ricky:
On Thursday, March 9, 2023 at 3:51:02 PM UTC-5, boB wrote:
On Thu, 9 Mar 2023 12:18:25 -0800 (PST), Ricky
gnuarm.del...@gmail.com> wrote:

I read some of the discussion on \"rail splitting\" and it occurred to me that there should be a market for these devices. I am working on a design that will run op amps from a single rail and I need a 6V level, that can both source and sink current. The board is really tight. Presently it is using zeners to set a level (one for each channel to reduce crosstalk), but I was looking at using an LDO, with a resistor to sink current.

But the new design is going to have some higher current requirements, and this would be a consistent load using the resistor. The obvious solution would be to set a reference point using resistors, and an op amp to provide the drive. The reference point doesn\'t need to be highly accurate or stable. A cap would reduce noise.

I\'m wondering if there are chips available that already do this providing say, 30 mA of drive/sink?
You would think there would be one of these but I still take 2 equal
value resistors and feed into a unity gain follower op-amp to supply
half-Vcc. Usually one half of a dual op-amp.

This would be a good use for a SOT-23 package....

But since it is just for bias, could use a SOT-23 NPN follower biased
up Vcc/2 + 0.65V or so.
The NPN follower would require the same resistor I would use with an LDO. So that\'s not much better, drawing the current all the time. In fact, when the load is pulling up, both the resistor and the LDO draw current!

npn+pnp follower, https://imgur.com/NhlLGGc

Does your drawing need a couple of diodes? Otherwise the output would have a dead band 1.something volts wide, no?

--

Rick C.

+- Get 1,000 miles of free Supercharging
+- Tesla referral code - https://ts.la/richard11209

 

[whit3rd]

On Thursday, March 9, 2023 at 12:56:22 PM UTC-8, Phil Hobbs wrote:

On 2023-03-09 15:50, boB wrote:
On Thu, 9 Mar 2023 12:18:25 -0800 (PST), Ricky
gnuarm.del...@gmail.com> wrote:

I read some of the discussion on \"rail splitting\" ...
The obvious solution would be to set a reference point using resistors, and an op amp to provide the drive.

You would think there would be one of these but I still take 2 equal
value resistors and feed into a unity gain follower op-amp...

TI sells a dedicated rail splitter chip, the TLE2426. It costs more
than a TCA0372 and doesn\'t have nearly the oomph.

It\'s easier to design with lots of power rails, like the old NIM +/- 24V, +/- 12V, +6, GND, and Vref
all from the standard power supplies. Scaling to fast low-V logic was just a point-of-load regulator
away, but nowadays... everyone wants a tiny box with a wallwart power solution.

The only solutions NOT discused here, are multioutput DC/DC converters (you can get REAL
ground, not just synthetic) and tapped battery stacks. Some of HP\'s old 200 series oscillators
used strings of NiCd batteries, and only trickle charged from AC.

Assuming your own power supply onboard, what\'s the ideal wallwart to start with?
Maybe a Cuk AC generator at 10V, 40 kHz or so, three-wire so the GND doesn\'t carry
power current? You can rectify or double/triple to get almost anything with not much
extra hardware. Or maybe -48VDC like POE, to keep wires slender and delivered
power quiet?

 

[Ricky]

On Thursday, March 9, 2023 at 8:53:24 PM UTC-5, whit3rd wrote:

On Thursday, March 9, 2023 at 12:56:22 PM UTC-8, Phil Hobbs wrote:
On 2023-03-09 15:50, boB wrote:
On Thu, 9 Mar 2023 12:18:25 -0800 (PST), Ricky
gnuarm.del...@gmail.com> wrote:

I read some of the discussion on \"rail splitting\" ...
The obvious solution would be to set a reference point using resistors, and an op amp to provide the drive.
You would think there would be one of these but I still take 2 equal
value resistors and feed into a unity gain follower op-amp...
TI sells a dedicated rail splitter chip, the TLE2426. It costs more
than a TCA0372 and doesn\'t have nearly the oomph.
It\'s easier to design with lots of power rails, like the old NIM +/- 24V, +/- 12V, +6, GND, and Vref
all from the standard power supplies. Scaling to fast low-V logic was just a point-of-load regulator
away, but nowadays... everyone wants a tiny box with a wallwart power solution.

The only solutions NOT discused here, are multioutput DC/DC converters (you can get REAL
ground, not just synthetic) and tapped battery stacks. Some of HP\'s old 200 series oscillators
used strings of NiCd batteries, and only trickle charged from AC.

Assuming your own power supply onboard, what\'s the ideal wallwart to start with?
Maybe a Cuk AC generator at 10V, 40 kHz or so, three-wire so the GND doesn\'t carry
power current? You can rectify or double/triple to get almost anything with not much
extra hardware. Or maybe -48VDC like POE, to keep wires slender and delivered
power quiet?

In this case, we are talking about a board, 4.5\" x 0.85\". Not much room for power converters, or even a wall wart connector. This is a daughtercard on a main board, which is plugged into a backplane that provides power to the rack. I got ±12V, 5V, 3.3V. The -12V is limited power, so it\'s not usable for the amplifier circuits.

That\'s why I need to provide a virtual ground at 6V. The previous generation did it simply with a couple of zener diodes, since the signal paths were all low current. But now there are some paths that have 50 ohms. Connecting them to the actual ground draws power all the time. The supply per module is limited and it has to drive 50 ohm loads, so I don\'t want to stress the main supply. I could add a cap to make it an AC ground, which would reduce the peak current. However, that\'s a large cap to get a 20 Hz passband..

An active virtual ground draws significantly less peak current, with one virtual ground for both channels on the module. Right now I\'m leaning toward the op amp approach. A three pin SC70 would certainly fit the bill though..

--

Rick C.

++ Get 1,000 miles of free Supercharging
++ Tesla referral code - https://ts.la/richard11209

 

[boB]

On Thu, 09 Mar 2023 16:04:33 -0800, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

On Thu, 09 Mar 2023 16:40:25 -0700, boB <boB@K7IQ.com> wrote:

On Thu, 09 Mar 2023 13:11:22 -0800, John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote:

On Thu, 9 Mar 2023 15:55:53 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-03-09 15:50, boB wrote:
On Thu, 9 Mar 2023 12:18:25 -0800 (PST), Ricky
gnuarm.deletethisbit@gmail.com> wrote:

I read some of the discussion on \"rail splitting\" and it occurred to me that there should be a market for these devices. I am working on a design that will run op amps from a single rail and I need a 6V level, that can both source and sink current. The board is really tight. Presently it is using zeners to set a level (one for each channel to reduce crosstalk), but I was looking at using an LDO, with a resistor to sink current.

But the new design is going to have some higher current requirements, and this would be a consistent load using the resistor. The obvious solution would be to set a reference point using resistors, and an op amp to provide the drive. The reference point doesn\'t need to be highly accurate or stable. A cap would reduce noise.

I\'m wondering if there are chips available that already do this providing say, 30 mA of drive/sink?


You would think there would be one of these but I still take 2 equal
value resistors and feed into a unity gain follower op-amp to supply
half-Vcc. Usually one half of a dual op-amp.

This would be a good use for a SOT-23 package....

But since it is just for bias, could use a SOT-23 NPN follower biased
up Vcc/2 + 0.65V or so.

boB


TI sells a dedicated rail splitter chip, the TLE2426. It costs more
than a TCA0372 and doesn\'t have nearly the oomph. Plus the TCA0372 is a
dual, so you can use the other half to do useful work too.

Cheers

Phil Hobbs

The TCA0372 data sheet only mentions +-15 supplies, but it actually
works at 5 volts between rails.

There\'s no power pad, but lots of V- pins on the 16-pin versions.


Interesting ! I would have possibly used one if it could split 3.3V
for LV applications.

But, that might be a single-sourced part ? Haven\'t looked at the
price.

boB

We pay 44 cents.

OK. That might work. Especially if space was at a premium which can
happen.

boB

 

[Phil Hobbs]

On 2023-03-09 20:53, whit3rd wrote:

On Thursday, March 9, 2023 at 12:56:22 PM UTC-8, Phil Hobbs wrote:
On 2023-03-09 15:50, boB wrote:
On Thu, 9 Mar 2023 12:18:25 -0800 (PST), Ricky
gnuarm.del...@gmail.com> wrote:

I read some of the discussion on \"rail splitting\" ...
The obvious solution would be to set a reference point using resistors, and an op amp to provide the drive.

You would think there would be one of these but I still take 2 equal
value resistors and feed into a unity gain follower op-amp...

TI sells a dedicated rail splitter chip, the TLE2426. It costs more
than a TCA0372 and doesn\'t have nearly the oomph.

It\'s easier to design with lots of power rails, like the old NIM +/- 24V, +/- 12V, +6, GND, and Vref
all from the standard power supplies. Scaling to fast low-V logic was just a point-of-load regulator
away, but nowadays... everyone wants a tiny box with a wallwart power solution.

The only solutions NOT discused here, are multioutput DC/DC converters (you can get REAL
ground, not just synthetic) and tapped battery stacks. Some of HP\'s old 200 series oscillators
used strings of NiCd batteries, and only trickle charged from AC.

Assuming your own power supply onboard, what\'s the ideal wallwart to start with?
Maybe a Cuk AC generator at 10V, 40 kHz or so, three-wire so the GND doesn\'t carry
power current? You can rectify or double/triple to get almost anything with not much
extra hardware. Or maybe -48VDC like POE, to keep wires slender and delivered
power quiet?

We use +24V medical-grade wall warts (SL Power ME10A2403B01) that come
with a set of international adapters.

We\'ve used the multiple-output things occasionally, but they all seem to
have these gruesome large-diameter, not-very-flexible cables with DIN
connectors. \'Clunky\' doesn\'t cover it.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[John Larkin]

On Fri, 10 Mar 2023 01:34:00 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-03-09 20:53, whit3rd wrote:
On Thursday, March 9, 2023 at 12:56:22?PM UTC-8, Phil Hobbs wrote:
On 2023-03-09 15:50, boB wrote:
On Thu, 9 Mar 2023 12:18:25 -0800 (PST), Ricky
gnuarm.del...@gmail.com> wrote:

I read some of the discussion on \"rail splitting\" ...
The obvious solution would be to set a reference point using resistors, and an op amp to provide the drive.

You would think there would be one of these but I still take 2 equal
value resistors and feed into a unity gain follower op-amp...

TI sells a dedicated rail splitter chip, the TLE2426. It costs more
than a TCA0372 and doesn\'t have nearly the oomph.

It\'s easier to design with lots of power rails, like the old NIM +/- 24V, +/- 12V, +6, GND, and Vref
all from the standard power supplies. Scaling to fast low-V logic was just a point-of-load regulator
away, but nowadays... everyone wants a tiny box with a wallwart power solution.

The only solutions NOT discused here, are multioutput DC/DC converters (you can get REAL
ground, not just synthetic) and tapped battery stacks. Some of HP\'s old 200 series oscillators
used strings of NiCd batteries, and only trickle charged from AC.

Assuming your own power supply onboard, what\'s the ideal wallwart to start with?
Maybe a Cuk AC generator at 10V, 40 kHz or so, three-wire so the GND doesn\'t carry
power current? You can rectify or double/triple to get almost anything with not much
extra hardware. Or maybe -48VDC like POE, to keep wires slender and delivered
power quiet?


We use +24V medical-grade wall warts (SL Power ME10A2403B01) that come
with a set of international adapters.

We have standardized on a 24 volt Phihong wart for most things. And a
24 volt laptop style supply for higher power.

We\'ve used the multiple-output things occasionally, but they all seem to
have these gruesome large-diameter, not-very-flexible cables with DIN
connectors. \'Clunky\' doesn\'t cover it.

Right. Make what you need from 24. That\'s easy nowadays.

 

[Phil Hobbs]

On 2023-03-10 01:42, John Larkin wrote:

On Fri, 10 Mar 2023 01:34:00 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-03-09 20:53, whit3rd wrote:
On Thursday, March 9, 2023 at 12:56:22?PM UTC-8, Phil Hobbs wrote:
On 2023-03-09 15:50, boB wrote:
On Thu, 9 Mar 2023 12:18:25 -0800 (PST), Ricky
gnuarm.del...@gmail.com> wrote:

I read some of the discussion on \"rail splitting\" ...
The obvious solution would be to set a reference point using resistors, and an op amp to provide the drive.

You would think there would be one of these but I still take 2 equal
value resistors and feed into a unity gain follower op-amp...

TI sells a dedicated rail splitter chip, the TLE2426. It costs more
than a TCA0372 and doesn\'t have nearly the oomph.

It\'s easier to design with lots of power rails, like the old NIM +/- 24V, +/- 12V, +6, GND, and Vref
all from the standard power supplies. Scaling to fast low-V logic was just a point-of-load regulator
away, but nowadays... everyone wants a tiny box with a wallwart power solution.

The only solutions NOT discused here, are multioutput DC/DC converters (you can get REAL
ground, not just synthetic) and tapped battery stacks. Some of HP\'s old 200 series oscillators
used strings of NiCd batteries, and only trickle charged from AC.

Assuming your own power supply onboard, what\'s the ideal wallwart to start with?
Maybe a Cuk AC generator at 10V, 40 kHz or so, three-wire so the GND doesn\'t carry
power current? You can rectify or double/triple to get almost anything with not much
extra hardware. Or maybe -48VDC like POE, to keep wires slender and delivered
power quiet?


We use +24V medical-grade wall warts (SL Power ME10A2403B01) that come
with a set of international adapters.

We have standardized on a 24 volt Phihong wart for most things. And a
24 volt laptop style supply for higher power.


We\'ve used the multiple-output things occasionally, but they all seem to
have these gruesome large-diameter, not-very-flexible cables with DIN
connectors. \'Clunky\' doesn\'t cover it.

Right. Make what you need from 24. That\'s easy nowadays.

It\'s less easy when doing wideband ultrasensitive measurements, but yeah.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[John Larkin]

On Fri, 10 Mar 2023 01:59:38 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-03-10 01:42, John Larkin wrote:
On Fri, 10 Mar 2023 01:34:00 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-03-09 20:53, whit3rd wrote:
On Thursday, March 9, 2023 at 12:56:22?PM UTC-8, Phil Hobbs wrote:
On 2023-03-09 15:50, boB wrote:
On Thu, 9 Mar 2023 12:18:25 -0800 (PST), Ricky
gnuarm.del...@gmail.com> wrote:

I read some of the discussion on \"rail splitting\" ...
The obvious solution would be to set a reference point using resistors, and an op amp to provide the drive.

You would think there would be one of these but I still take 2 equal
value resistors and feed into a unity gain follower op-amp...

TI sells a dedicated rail splitter chip, the TLE2426. It costs more
than a TCA0372 and doesn\'t have nearly the oomph.

It\'s easier to design with lots of power rails, like the old NIM +/- 24V, +/- 12V, +6, GND, and Vref
all from the standard power supplies. Scaling to fast low-V logic was just a point-of-load regulator
away, but nowadays... everyone wants a tiny box with a wallwart power solution.

The only solutions NOT discused here, are multioutput DC/DC converters (you can get REAL
ground, not just synthetic) and tapped battery stacks. Some of HP\'s old 200 series oscillators
used strings of NiCd batteries, and only trickle charged from AC.

Assuming your own power supply onboard, what\'s the ideal wallwart to start with?
Maybe a Cuk AC generator at 10V, 40 kHz or so, three-wire so the GND doesn\'t carry
power current? You can rectify or double/triple to get almost anything with not much
extra hardware. Or maybe -48VDC like POE, to keep wires slender and delivered
power quiet?


We use +24V medical-grade wall warts (SL Power ME10A2403B01) that come
with a set of international adapters.

We have standardized on a 24 volt Phihong wart for most things. And a
24 volt laptop style supply for higher power.


We\'ve used the multiple-output things occasionally, but they all seem to
have these gruesome large-diameter, not-very-flexible cables with DIN
connectors. \'Clunky\' doesn\'t cover it.

Right. Make what you need from 24. That\'s easy nowadays.

It\'s less easy when doing wideband ultrasensitive measurements, but yeah.

Cheers

Phil Hobbs

Our critical measurement is jitter, and a typical target is a few ps
RMS. Switchers can play hell with that, especially ones that make,
say, 400 MHz bursts. It\'s easier to prevent those from happening on a
board, as compared to trying to filter them afterwards.

Another jitter contributor is the modulation of logic device prop
delay by supply voltage ripple, which happens at any frequency but can
be filtered. FPGAs are horribly sensitive, prop delay vs Vcore.

We designed one delay generator that had the fast trigger path go
through an Artix7 FPGA. Big mistake. Delay changed 1 ps for a 70 uV
core supply change. I tore up the fast path and made it all discrete
logic and cut jitter and insertion delay both.

FPGAs are getting faster inside and slower pin-to-pin, which seems
strange to me. So we keep designing with discrete transistors and
diodes and gates and flops, kind of like you use discretes for the
critical bits. A diode OR gate works pretty well.

There are some logic parts with femtosecond jitter, but they are too
expensive for most uses.