current limiter chip...

J

John Larkin

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I want a small current limiter chip.

Sot-23 size
Low voltage dropout
Current and thermal limited
Resistor programmable limit
Reasonable price
Available!

Does anybody know of one?
 
On Friday, September 2, 2022 at 10:44:55 AM UTC-7, John Larkin wrote:
I want a small current limiter chip.

Sot-23 size
Low voltage dropout
Current and thermal limited
Resistor programmable limit
Reasonable price
Available!

Does anybody know of one?
Click to expand...

Page 17, fig 39:
https://www.ti.com/lit/ds/symlink/tl431-q1.pdf
 
On Friday, September 2, 2022 at 1:44:55 PM UTC-4, John Larkin wrote:
I want a small current limiter chip.

Sot-23 size
Low voltage dropout
Current and thermal limited
Resistor programmable limit
Reasonable price
Available!

Does anybody know of one?
Click to expand...

Those relatively high current monolithic lithium battery chargers use that dual MOSFET technique in which a second small scale MOSFET has the same VGS as the higher current charging path MOSFET.
 
On Friday, September 2, 2022 at 10:44:55 AM UTC-7, John Larkin wrote:
I want a small current limiter chip.

Sot-23 size
Low voltage dropout
Current and thermal limited
Resistor programmable limit
Click to expand...

Input voltage range?
Precision?
Bandwidth?

It takes an op amp with one-rail input, and voltage reference, and maybe pass
transistor, to do that, using three pins. Low voltage range means only
small current-sense resistance is acceptable, and precision will suffer when
offset voltages dominate.

Reasonable price
Available!
Click to expand...

Some of the LED drive circuits are VERY available, and limit current... but
do it with switch-off transients. And with the right power available, and
into a low-Z load, a surface-mount resistor (0805) would work.
 
John Larkin <jlarkin@highland_atwork_technology.com> Wrote in message:r
> I want a small current limiter chip.Sot-23 sizeLow voltage dropoutCurrent and thermal limitedResistor programmable limitReasonable priceAvailable!Does anybody know of one?

Mp5032
USB current limiter/switch

Cheers
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On Fri, 2 Sep 2022 10:52:00 -0700 (PDT), Ed Lee
<edward.ming.lee@gmail.com> wrote:

On Friday, September 2, 2022 at 10:44:55 AM UTC-7, John Larkin wrote:
I want a small current limiter chip.

Sot-23 size
Low voltage dropout
Current and thermal limited
Resistor programmable limit
Reasonable price
Available!

Does anybody know of one?

Page 17, fig 39:
https://www.ti.com/lit/ds/symlink/tl431-q1.pdf
Click to expand...

Sure, I can design a circuit with parts. That one is not low dropout
and does not thermal limit.
 
On Fri, 2 Sep 2022 16:12:09 -0400 (EDT), Martin Rid
<martin_riddle@verison.net> wrote:

John Larkin <jlarkin@highland_atwork_technology.com> Wrote in message:r
I want a small current limiter chip.Sot-23 sizeLow voltage dropoutCurrent and thermal limitedResistor programmable limitReasonable priceAvailable!Does anybody know of one?

Mp5032
USB current limiter/switch

Cheers
Click to expand...

3 amps would fry the thing I want to protect.
 
John Larkin <jlarkin@highland_atwork_technology.com> Wrote in message:r
> On Fri, 2 Sep 2022 16:12:09 -0400 (EDT), Martin Rid<martin_riddle@verison.net> wrote:>John Larkin <jlarkin@highland_atwork_technology.com> Wrote in message:r>> I want a small current limiter chip.Sot-23 sizeLow voltage dropoutCurrent and thermal limitedResistor programmable limitReasonable priceAvailable!Does anybody know of one?>>Mp5032>USB current limiter/switch>>Cheers3 amps would fry the thing I want to protect.

The curve for Rlimit goes down to 500ma.
Is it less than 500ma?

Cheers
--


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On Friday, September 2, 2022 at 10:44:55 AM UTC-7, John Larkin wrote:
I want a small current limiter chip.

Sot-23 size
Low voltage dropout
Current and thermal limited
Resistor programmable limit
Click to expand...

This seems appropriate

<https://www.diodes.com/assets/Datasheets/BCR430UW6.pdf>

Reasonable price
Available!
Click to expand...

DigiKey claims to have stock.
It\'s a sink, not a source, but... regulated for sure.
You say \'limiter\' which is a looser specification, and maybe a PTC resistor is just as good.
 
On Friday, September 2, 2022 at 1:58:09 PM UTC-7, John Larkin wrote:
On Fri, 2 Sep 2022 16:12:09 -0400 (EDT), Martin Rid
martin...@verison.net> wrote:

John Larkin <jlarkin@highland_atwork_technology.com> Wrote in message:r
I want a small current limiter chip.Sot-23 sizeLow voltage dropoutCurrent and thermal limitedResistor programmable limitReasonable priceAvailable!Does anybody know of one?

Mp5032
USB current limiter/switch

Cheers
3 amps would fry the thing I want to protect.
Click to expand...

What I/O voltage?
 
On Fri, 2 Sep 2022 17:01:45 -0400 (EDT), Martin Rid
<martin_riddle@verison.net> wrote:

John Larkin <jlarkin@highland_atwork_technology.com> Wrote in message:r
On Fri, 2 Sep 2022 16:12:09 -0400 (EDT), Martin Rid<martin_riddle@verison.net> wrote:>John Larkin <jlarkin@highland_atwork_technology.com> Wrote in message:r>> I want a small current limiter chip.Sot-23 sizeLow voltage dropoutCurrent and thermal limitedResistor programmable limitReasonable priceAvailable!Does anybody know of one?>>Mp5032>USB current limiter/switch>>Cheers3 amps would fry the thing I want to protect.

The curve for Rlimit goes down to 500ma.
Click to expand...

\"Set the current limit level. Place a resistor between ILIM and GND to
achieve a high accuracy current limit. The current limit threshold
varies versus the output voltage to maintain a fairly constant output
power limit.\"

Sounds tricky. And maybe it needs to do a handshake with a USB device.



Is it less than 500ma?

Cheers
Click to expand...

The current (no pun) problem is to protect a pulse output stage that
makes 5 volts out, from a 5 volt supply. It normally has a 50 ohm
series resistor from the driver to the connector, but some customers
want us to be able to programmably short that resistor so they get 5
volts - not 2.5 - into their 50 ohm load.

That current limit should be a bit above 100 mA. But the current limit
problem keeps coming up.
 
On Fri, 2 Sep 2022 14:59:52 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

On Friday, September 2, 2022 at 10:44:55 AM UTC-7, John Larkin wrote:
I want a small current limiter chip.

Sot-23 size
Low voltage dropout
Current and thermal limited
Resistor programmable limit

This seems appropriate

https://www.diodes.com/assets/Datasheets/BCR430UW6.pdf

Reasonable price
Available!
Click to expand...

I don\'t understand that part. Does the mosfet switch hard to ground
and PWM to tune the average current?




DigiKey claims to have stock.
It\'s a sink, not a source, but... regulated for sure.
You say \'limiter\' which is a looser specification, and maybe a PTC resistor is just as good.
Click to expand...
 
On Fri, 02 Sep 2022 10:44:42 -0700, John Larkin
<jlarkin@highland_atwork_technology.com> wrote:

I want a small current limiter chip.

Sot-23 size
Low voltage dropout
Current and thermal limited
Resistor programmable limit
Reasonable price
Available!

Does anybody know of one?
Click to expand...

MAX4995 is close but it\'s $5 in small quantities.
 
On Friday, September 2, 2022 at 4:25:52 PM UTC-7, John Larkin wrote:
On Fri, 2 Sep 2022 14:59:52 -0700 (PDT), whit3rd <whi...@gmail.com
wrote:
On Friday, September 2, 2022 at 10:44:55 AM UTC-7, John Larkin wrote:
I want a small current limiter chip.

This seems appropriate

https://www.diodes.com/assets/Datasheets/BCR430UW6.pdf

I don\'t understand that part. Does the mosfet switch hard to ground
and PWM to tune the average current?
Click to expand...

There\'s no logic in the connections they show
in the lame block diagram. Clearly, the pass MOSFET has
to have its source lead connected to the Rext or \'typical application\'
won\'t work. I suspect the op amp output goes to the \'driver\'
input, also not-as-depicted.

It wouldn\'t be reasonable to PWM and not have any timing components.
 
John Larkin <jlarkin@highland_atwork_technology.com> Wrote in message:r
On Fri, 2 Sep 2022 17:01:45 -0400 (EDT), Martin Rid<martin_riddle@verison.net> wrote:>John Larkin <jlarkin@highland_atwork_technology.com> Wrote in message:r>> On Fri, 2 Sep 2022 16:12:09 -0400 (EDT), Martin Rid<martin_riddle@verison.net> wrote:>John Larkin <jlarkin@highland_atwork_technology.com> Wrote in message:r>> I want a small current limiter chip.Sot-23 sizeLow voltage dropoutCurrent and thermal limitedResistor programmable limitReasonable priceAvailable!Does anybody know of one?>>Mp5032>USB current limiter/switch>>Cheers3 amps would fry the thing I want to protect.>>The curve for Rlimit goes down to 500ma.\"Set the current limit level. Place a resistor between ILIM and GND toachieve a high accuracy current limit. The current limit thresholdvaries versus the output voltage to maintain a fairly constant outputpower limit.\"Sounds tricky. And maybe it needs to do a handshake with a USB device.>Is it less than 500ma?>>CheersThe current (no pun) problem is to protect a pulse output stage thatmakes 5 volts out, from a 5 volt supply. It normally has a 50 ohmseries resistor from the driver to the connector, but some customerswant us to be able to programmably short that resistor s
o they get 5volts - not 2.5 - into their 50 ohm load.That current limit should be a bit above 100 mA. But the current limitproblem keeps coming up.
Click to expand...

Maybe there is someone that makes a high side switch with an
adjustable current limit.

Cheers
--


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John Larkin <jlarkin@highland_atwork_technology.com> Wrote in message:r
On Fri, 2 Sep 2022 17:01:45 -0400 (EDT), Martin Rid<martin_riddle@verison.net> wrote:>John Larkin <jlarkin@highland_atwork_technology.com> Wrote in message:r>> On Fri, 2 Sep 2022 16:12:09 -0400 (EDT), Martin Rid<martin_riddle@verison.net> wrote:>John Larkin <jlarkin@highland_atwork_technology.com> Wrote in message:r>> I want a small current limiter chip.Sot-23 sizeLow voltage dropoutCurrent and thermal limitedResistor programmable limitReasonable priceAvailable!Does anybody know of one?>>Mp5032>USB current limiter/switch>>Cheers3 amps would fry the thing I want to protect.>>The curve for Rlimit goes down to 500ma.\"Set the current limit level. Place a resistor between ILIM and GND toachieve a high accuracy current limit. The current limit thresholdvaries versus the output voltage to maintain a fairly constant outputpower limit.\"Sounds tricky. And maybe it needs to do a handshake with a USB device.>Is it less than 500ma?>>CheersThe current (no pun) problem is to protect a pulse output stage thatmakes 5 volts out, from a 5 volt supply. It normally has a 50 ohmseries resistor from the driver to the connector, but some customerswant us to be able to programmably short that resistor s
o they get 5volts - not 2.5 - into their 50 ohm load.That current limit should be a bit above 100 mA. But the current limitproblem keeps coming up.
Click to expand...

NCV47722

Similar, but lower current.

Cheers
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https://piaohong.s3-us-west-2.amazonaws.com/usenet/index.html
 
On Fri, 02 Sep 2022 10:44:42 -0700, John Larkin
<jlarkin@highland_atwork_technology.com> wrote:

I want a small current limiter chip.

Sot-23 size
Low voltage dropout
Current and thermal limited
Resistor programmable limit
Reasonable price
Available!

Does anybody know of one?
Click to expand...

Here\'s an idea. The output is usually 50 ohms, and in that case it\'s
OK if the customer sets the output high and shorts it to ground. But
in lo-Z mode we short the 50r resistor with the TS3USB thing and the
customer can ground the output and fry our drivers.

The idea is to sense too much supply current and set a flop that puts
us back into 50 ohm mode. A periodic clock tries to clear the flop, 1
Hz maybe.

https://www.dropbox.com/s/cy1oj1i1fbn423i/T560_Out_Ilim.jpg?raw=1

It\'s a sense resistor and 1/2 a dual comparator and a tiny flop per
channel.

We could run the comparator output into our Zynq FPGA and let it do
the shutdown and reset timing, but we\'re about out of pins. If we can
scrounge four pins, it becomes one resistor and 1/2 a dual comparator
per channel.

The USB switches can be used as zero-delay logic elements. That\'s
handy in several places as we are fighting to keep the box
trigger-to-output delay below 20 ns.
 
On a sunny day (Fri, 02 Sep 2022 16:20:36 -0700) it happened John Larkin
<jlarkin@highland_atwork_technology.com> wrote in
<f435hhdu7fk9j8beg5h2qa3nah5mf6anoc@4ax.com>:

The current (no pun) problem is to protect a pulse output stage that
makes 5 volts out, from a 5 volt supply. It normally has a 50 ohm
series resistor from the driver to the connector, but some customers
want us to be able to programmably short that resistor so they get 5
volts - not 2.5 - into their 50 ohm load.

That current limit should be a bit above 100 mA. But the current limit
problem keeps coming up.
Click to expand...

Switch to a 10 V supply?
 
John Larkin wrote:
On Fri, 2 Sep 2022 17:01:45 -0400 (EDT), Martin Rid
martin_riddle@verison.net> wrote:

John Larkin <jlarkin@highland_atwork_technology.com> Wrote in message:r
On Fri, 2 Sep 2022 16:12:09 -0400 (EDT), Martin Rid<martin_riddle@verison.net> wrote:>John Larkin <jlarkin@highland_atwork_technology.com> Wrote in message:r>> I want a small current limiter chip.Sot-23 sizeLow voltage dropoutCurrent and thermal limitedResistor programmable limitReasonable priceAvailable!Does anybody know of one?>>Mp5032>USB current limiter/switch>>Cheers3 amps would fry the thing I want to protect.

The curve for Rlimit goes down to 500ma.

\"Set the current limit level. Place a resistor between ILIM and GND to
achieve a high accuracy current limit. The current limit threshold
varies versus the output voltage to maintain a fairly constant output
power limit.\"

Sounds tricky. And maybe it needs to do a handshake with a USB device.



Is it less than 500ma?

Cheers

The current (no pun) problem is to protect a pulse output stage that
makes 5 volts out, from a 5 volt supply. It normally has a 50 ohm
series resistor from the driver to the connector, but some customers
want us to be able to programmably short that resistor so they get 5
volts - not 2.5 - into their 50 ohm load.

That current limit should be a bit above 100 mA. But the current limit
problem keeps coming up.
Click to expand...

Hmm. My usual approach is to put a resistor in the supply lead, with a
nice beefy bypass cap to let the output amp ride over transients. That
won\'t work unless you can power the output amp from a bit taller supply.

When there\'s at least a bit of headroom available, and the current limit
can be a bit sloppy, I\'ve also used a low-sat PNP transistor with a
resistor to ground from the base. This keeps the PNP in saturation in
normal use, and rides over brief transients, even pretty large ones.
Longer transients deplete the stored charge in the base, so the
collector voltage collapses in a few microseconds.

(I realize you\'re looking for a specific integrated solution to a
precise problem, but (a) I know of none, and (b) general on-topic
discussion is always good.)

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
 
On Sat, 3 Sep 2022 14:21:40 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin wrote:
On Fri, 2 Sep 2022 17:01:45 -0400 (EDT), Martin Rid
martin_riddle@verison.net> wrote:

John Larkin <jlarkin@highland_atwork_technology.com> Wrote in message:r
On Fri, 2 Sep 2022 16:12:09 -0400 (EDT), Martin Rid<martin_riddle@verison.net> wrote:>John Larkin <jlarkin@highland_atwork_technology.com> Wrote in message:r>> I want a small current limiter chip.Sot-23 sizeLow voltage dropoutCurrent and thermal limitedResistor programmable limitReasonable priceAvailable!Does anybody know of one?>>Mp5032>USB current limiter/switch>>Cheers3 amps would fry the thing I want to protect.

The curve for Rlimit goes down to 500ma.

\"Set the current limit level. Place a resistor between ILIM and GND to
achieve a high accuracy current limit. The current limit threshold
varies versus the output voltage to maintain a fairly constant output
power limit.\"

Sounds tricky. And maybe it needs to do a handshake with a USB device.



Is it less than 500ma?

Cheers

The current (no pun) problem is to protect a pulse output stage that
makes 5 volts out, from a 5 volt supply. It normally has a 50 ohm
series resistor from the driver to the connector, but some customers
want us to be able to programmably short that resistor so they get 5
volts - not 2.5 - into their 50 ohm load.

That current limit should be a bit above 100 mA. But the current limit
problem keeps coming up.


Hmm. My usual approach is to put a resistor in the supply lead, with a
nice beefy bypass cap to let the output amp ride over transients. That
won\'t work unless you can power the output amp from a bit taller supply.

When there\'s at least a bit of headroom available, and the current limit
can be a bit sloppy, I\'ve also used a low-sat PNP transistor with a
resistor to ground from the base. This keeps the PNP in saturation in
normal use, and rides over brief transients, even pretty large ones.
Longer transients deplete the stored charge in the base, so the
collector voltage collapses in a few microseconds.

(I realize you\'re looking for a specific integrated solution to a
precise problem, but (a) I know of none, and (b) general on-topic
discussion is always good.)

Cheers

Phil Hobbs
Click to expand...

The part I want seems pretty obvious, but nobody seems to make it.

Somebody, National maybe, once sold a PNP transistor with a super
tight beta spec, specifically as a current limiter. But it wouldn\'t
thermal limit.

One alternate is an LM317 type reg with a big resistor from +12 volts
to limit current. That\'s klunky.
 
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