Hi, all,
I'm designing a gizmo that needs current monitoring inside bootstrap
loops, with the sense resistors near the +- supply rails. I want to get >good PSR without using choppers, because I don't trust them to have low >enough kickout.
There are lots of nice chips for the positive rail, mostly 5V with a
wide CM range and costing eleven cents (positively Joergesque).
However, none of them allows operation more than epsilon below their
ground reference (-0.1V or so). Thus the chip's supplies would have to
be VEE+5V to VEE, and it would produce an output down near the negative >rail. Inconvenient.
So the thought is to use something like a ZVCT213 ><https://www.diodes.com/assets/Datasheets/ZXCT21x.pdf> running from VEE
to +5, with its output reference pin grounded.
This looks like it should work, but in the circs I'm going to have to
try it out first--I care about stuff like input capacitance to the
supply rails.
Any of you lot tried measuring negative supply current with one of these >things, or anything similar?
Thanks
Phil Hobbs
Hi, all,
I'm designing a gizmo that needs current monitoring inside bootstrap
loops, with the sense resistors near the +- supply rails. I want to get good PSR without using choppers, because I don't trust them to have low enough kickout.
There are lots of nice chips for the positive rail, mostly 5V with a
wide CM range and costing eleven cents (positively Joergesque).
However, none of them allows operation more than epsilon below their
ground reference (-0.1V or so). Thus the chip's supplies would have to
be VEE+5V to VEE, and it would produce an output down near the negative rail. Inconvenient.
So the thought is to use something like a ZVCT213 <https://www.diodes.com/assets/Datasheets/ZXCT21x.pdf> running from VEE
to +5, with its output reference pin grounded.
This looks like it should work, but in the circs I'm going to have to
try it out first--I care about stuff like input capacitance to the
supply rails.
Any of you lot tried measuring negative supply current with one of these things, or anything similar?
Thanks
Phil Hobbs
On Thu, 22 Jan 2026 12:11:09 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
Hi, all,
I'm designing a gizmo that needs current monitoring inside
bootstrap loops, with the sense resistors near the +- supply rails.
I want to get good PSR without using choppers, because I don't
trust them to have low enough kickout.
There are lots of nice chips for the positive rail, mostly 5V with
a wide CM range and costing eleven cents (positively Joergesque).
However, none of them allows operation more than epsilon below
their ground reference (-0.1V or so). Thus the chip's supplies
would have to be VEE+5V to VEE, and it would produce an output down
near the negative rail. Inconvenient.
So the thought is to use something like a ZVCT213
<https://www.diodes.com/assets/Datasheets/ZXCT21x.pdf> running from
VEE to +5, with its output reference pin grounded.
This looks like it should work, but in the circs I'm going to have
to try it out first--I care about stuff like input capacitance to
the supply rails.
Any of you lot tried measuring negative supply current with one of
these things, or anything similar?
Thanks
Phil Hobbs
We're using a shunt resistor and an INA241 in one product. It claims
to work to -5 volts on the shunt. The product is in development
still, FPGAs and code and such, so I can't swear it works well.
Our current is bipolar so zero current parks the INA output halfway
up.
I'm using a 10-amp Hall chip on another product and it seems to be
nice. You may be running nanoamps.
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
Hi, all,
I'm designing a gizmo that needs current monitoring inside bootstrap
loops, with the sense resistors near the +- supply rails. I want to get
good PSR without using choppers, because I don't trust them to have low
enough kickout.
There are lots of nice chips for the positive rail, mostly 5V with a
wide CM range and costing eleven cents (positively Joergesque).
However, none of them allows operation more than epsilon below their
ground reference (-0.1V or so). Thus the chip's supplies would have to
be VEE+5V to VEE, and it would produce an output down near the negative
rail. Inconvenient.
So the thought is to use something like a ZVCT213
<https://www.diodes.com/assets/Datasheets/ZXCT21x.pdf> running from VEE
to +5, with its output reference pin grounded.
This looks like it should work, but in the circs I'm going to have to
try it out first--I care about stuff like input capacitance to the
supply rails.
Any of you lot tried measuring negative supply current with one of these
things, or anything similar?
Thanks
Phil Hobbs
I have just used vanilla op-amps for low side sensing, nothing gaudy. Just curious why you mentioned chopper amp kickout, how high value are your
shunt resistors?
That ZXCT family is interesting, thanks, accurate but not fast.
On 2026-01-22 14:33, john larkin wrote:
On Thu, 22 Jan 2026 12:11:09 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
Hi, all,
I'm designing a gizmo that needs current monitoring inside
bootstrap loops, with the sense resistors near the +- supply rails.
I want to get good PSR without using choppers, because I don't
trust them to have low enough kickout.
There are lots of nice chips for the positive rail, mostly 5V with
a wide CM range and costing eleven cents (positively Joergesque).
However, none of them allows operation more than epsilon below
their ground reference (-0.1V or so). Thus the chip's supplies
would have to be VEE+5V to VEE, and it would produce an output down
near the negative rail. Inconvenient.
So the thought is to use something like a ZVCT213
<https://www.diodes.com/assets/Datasheets/ZXCT21x.pdf> running from
VEE to +5, with its output reference pin grounded.
This looks like it should work, but in the circs I'm going to have
to try it out first--I care about stuff like input capacitance to
the supply rails.
Any of you lot tried measuring negative supply current with one of
these things, or anything similar?
Thanks
Phil Hobbs
We're using a shunt resistor and an INA241 in one product. It claims
to work to -5 volts on the shunt. The product is in development
still, FPGAs and code and such, so I can't swear it works well.
Nice part. Of course it ought to be for $3. ;)
That "enhanced PWM rejection" part worries me slightly--sounds like it
might have some kickout, which I really do not want. The 0.01% accuracy
and CMR (166 dB!) are pretty cool though. I'll get a few to try out.
Nah, not this time. Generally 50 uA - 5 mA per photodiode. It's a >differential laser noise canceller with some nice comfort features.
Our current is bipolar so zero current parks the INA output halfway
up.
I'm using a 10-amp Hall chip on another product and it seems to be
nice. You may be running nanoamps.
I ordered some of these to try out:
?ZXCT213CDW
?INA241A2IDDFR?
MCP6C04T-020E/CHY?
MCP6C26T-050E/LTY?
ZXCT181QA1W6
Should be here in the depths of the deepfreeze next week. We'll see!
Cheers
Phil Hobbs
On 2026-01-22 14:50, piglet wrote:
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
Hi, all,
I'm designing a gizmo that needs current monitoring inside bootstrap
loops, with the sense resistors near the +- supply rails. I want to get >>> good PSR without using choppers, because I don't trust them to have low
enough kickout.
There are lots of nice chips for the positive rail, mostly 5V with a
wide CM range and costing eleven cents (positively Joergesque).
However, none of them allows operation more than epsilon below their
ground reference (-0.1V or so). Thus the chip's supplies would have to
be VEE+5V to VEE, and it would produce an output down near the negative
rail. Inconvenient.
So the thought is to use something like a ZVCT213
<https://www.diodes.com/assets/Datasheets/ZXCT21x.pdf> running from VEE
to +5, with its output reference pin grounded.
This looks like it should work, but in the circs I'm going to have to
try it out first--I care about stuff like input capacitance to the
supply rails.
Any of you lot tried measuring negative supply current with one of these >>> things, or anything similar?
Thanks
Phil Hobbs
I have just used vanilla op-amps for low side sensing, nothing gaudy. Just >> curious why you mentioned chopper amp kickout, how high value are your
shunt resistors?
About 20 to 100 ohms, depending on the minimum gain of the sense amp
family. They're hanging in midair, though, between the photodiode and a >~1-ohm bootstrap. I'm bypassing them with 470 nF or so, and the sense
amp's input resistors are theoretically about 100k, so the kickout
should theoretically be pretty low. On the other hand, some customers
are going to be looking at the output with a spectrum analyzer....
I could use an op amp and a transistor to do the sensing and generate a >current output to do the level shifting all in one go, but it's really
hard to get good enough CMR using discrete resistors. It's also five or
six extra parts per sensor, and I need three of them. I'll certainly do >that if I have to.
That ZXCT family is interesting, thanks, accurate but not fast.
Cheap, too!
Cheers
Phil Hobbs
On Thu, 22 Jan 2026 16:56:51 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
On 2026-01-22 14:33, john larkin wrote:
On Thu, 22 Jan 2026 12:11:09 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
Hi, all,
I'm designing a gizmo that needs current monitoring inside
bootstrap loops, with the sense resistors near the +- supply rails.
I want to get good PSR without using choppers, because I don't
trust them to have low enough kickout.
There are lots of nice chips for the positive rail, mostly 5V with
a wide CM range and costing eleven cents (positively Joergesque).
However, none of them allows operation more than epsilon below
their ground reference (-0.1V or so). Thus the chip's supplies
would have to be VEE+5V to VEE, and it would produce an output down
near the negative rail. Inconvenient.
So the thought is to use something like a ZVCT213
<https://www.diodes.com/assets/Datasheets/ZXCT21x.pdf> running from
VEE to +5, with its output reference pin grounded.
This looks like it should work, but in the circs I'm going to have
to try it out first--I care about stuff like input capacitance to
the supply rails.
Any of you lot tried measuring negative supply current with one of
these things, or anything similar?
Thanks
Phil Hobbs
We're using a shunt resistor and an INA241 in one product. It claims
to work to -5 volts on the shunt. The product is in development
still, FPGAs and code and such, so I can't swear it works well.
Nice part. Of course it ought to be for $3. ;)
I can sell them to you for $2.
That "enhanced PWM rejection" part worries me slightly--sounds like it
might have some kickout, which I really do not want. The 0.01% accuracy
and CMR (166 dB!) are pretty cool though. I'll get a few to try out.
The PWM thing sounds like filtering or spike rejection. We're using it
in a barely-filtered 500 KHz 50-volt h-bridge output and the resulting
ADC noise is pretty good.
What bw do you need?
I'll email you our schematic.
Stay warm!
On Thu, 22 Jan 2026 16:56:51 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
On 2026-01-22 14:33, john larkin wrote:
On Thu, 22 Jan 2026 12:11:09 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
Hi, all,
I'm designing a gizmo that needs current monitoring inside
bootstrap loops, with the sense resistors near the +- supply rails.
I want to get good PSR without using choppers, because I don't
trust them to have low enough kickout.
There are lots of nice chips for the positive rail, mostly 5V with
a wide CM range and costing eleven cents (positively Joergesque).
However, none of them allows operation more than epsilon below
their ground reference (-0.1V or so). Thus the chip's supplies
would have to be VEE+5V to VEE, and it would produce an output down
near the negative rail. Inconvenient.
So the thought is to use something like a ZVCT213
<https://www.diodes.com/assets/Datasheets/ZXCT21x.pdf> running from
VEE to +5, with its output reference pin grounded.
This looks like it should work, but in the circs I'm going to have
to try it out first--I care about stuff like input capacitance to
the supply rails.
Any of you lot tried measuring negative supply current with one of
these things, or anything similar?
Thanks
Phil Hobbs
We're using a shunt resistor and an INA241 in one product. It claims
to work to -5 volts on the shunt. The product is in development
still, FPGAs and code and such, so I can't swear it works well.
Nice part. Of course it ought to be for $3. ;)
I can sell them to you for $2.
That "enhanced PWM rejection" part worries me slightly--sounds like it
might have some kickout, which I really do not want. The 0.01% accuracy
and CMR (166 dB!) are pretty cool though. I'll get a few to try out.
The PWM thing sounds like filtering or spike rejection. We're using it
in a barely-filtered 500 KHz 50-volt h-bridge output and the resulting
ADC noise is pretty good.
What bw do you need?
I'll email you our schematic.
Stay warm!
Nah, not this time. Generally 50 uA - 5 mA per photodiode. It's a
Our current is bipolar so zero current parks the INA output halfway
up.
I'm using a 10-amp Hall chip on another product and it seems to be
nice. You may be running nanoamps.
differential laser noise canceller with some nice comfort features.
I ordered some of these to try out:
?ZXCT213CDW
?INA241A2IDDFR?
MCP6C04T-020E/CHY?
MCP6C26T-050E/LTY?
ZXCT181QA1W6
Should be here in the depths of the deepfreeze next week. We'll see!
Cheers
Phil Hobbs
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
On 1/22/2026 5:37 PM, john larkin wrote:
On Thu, 22 Jan 2026 16:56:51 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
On 2026-01-22 14:33, john larkin wrote:
On Thu, 22 Jan 2026 12:11:09 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
Hi, all,
I'm designing a gizmo that needs current monitoring inside
bootstrap loops, with the sense resistors near the +- supply rails.
I want to get good PSR without using choppers, because I don't
trust them to have low enough kickout.
There are lots of nice chips for the positive rail, mostly 5V with
a wide CM range and costing eleven cents (positively Joergesque).
However, none of them allows operation more than epsilon below
their ground reference (-0.1V or so). Thus the chip's supplies
would have to be VEE+5V to VEE, and it would produce an output down
near the negative rail. Inconvenient.
So the thought is to use something like a ZVCT213
<https://www.diodes.com/assets/Datasheets/ZXCT21x.pdf> running from
VEE to +5, with its output reference pin grounded.
This looks like it should work, but in the circs I'm going to have
to try it out first--I care about stuff like input capacitance to
the supply rails.
Any of you lot tried measuring negative supply current with one of
these things, or anything similar?
Thanks
Phil Hobbs
We're using a shunt resistor and an INA241 in one product. It claims
to work to -5 volts on the shunt. The product is in development
still, FPGAs and code and such, so I can't swear it works well.
Nice part. Of course it ought to be for $3. ;)
I can sell them to you for $2.
That "enhanced PWM rejection" part worries me slightly--sounds like it
might have some kickout, which I really do not want. The 0.01% accuracy >>> and CMR (166 dB!) are pretty cool though. I'll get a few to try out.
The PWM thing sounds like filtering or spike rejection. We're using it
in a barely-filtered 500 KHz 50-volt h-bridge output and the resulting
ADC noise is pretty good.
What bw do you need?
I'll email you our schematic.
Stay warm!
We'll need some "global warming" to do that.
Phil's likely to be a bit colder than me - I'm
near Long Island Sound, he's about 40 miles north.
Ed
Nah, not this time. Generally 50 uA - 5 mA per photodiode. It's a
Our current is bipolar so zero current parks the INA output halfway
up.
I'm using a 10-amp Hall chip on another product and it seems to be
nice. You may be running nanoamps.
differential laser noise canceller with some nice comfort features.
I ordered some of these to try out:
?ZXCT213CDW
?INA241A2IDDFR?
MCP6C04T-020E/CHY?
MCP6C26T-050E/LTY?
ZXCT181QA1W6
Should be here in the depths of the deepfreeze next week. We'll see!
Cheers
Phil Hobbs
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
On Thu, 22 Jan 2026 21:30:04 -0500, ehsjr <ehsjr@verizon.net> wrote:
On 1/22/2026 5:37 PM, john larkin wrote:
On Thu, 22 Jan 2026 16:56:51 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
On 2026-01-22 14:33, john larkin wrote:
On Thu, 22 Jan 2026 12:11:09 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
Hi, all,
I'm designing a gizmo that needs current monitoring inside
bootstrap loops, with the sense resistors near the +- supply rails. >>>>>> I want to get good PSR without using choppers, because I don't
trust them to have low enough kickout.
There are lots of nice chips for the positive rail, mostly 5V with >>>>>> a wide CM range and costing eleven cents (positively Joergesque).
However, none of them allows operation more than epsilon below
their ground reference (-0.1V or so). Thus the chip's supplies
would have to be VEE+5V to VEE, and it would produce an output down >>>>>> near the negative rail. Inconvenient.
So the thought is to use something like a ZVCT213
<https://www.diodes.com/assets/Datasheets/ZXCT21x.pdf> running from >>>>>> VEE to +5, with its output reference pin grounded.
This looks like it should work, but in the circs I'm going to have >>>>>> to try it out first--I care about stuff like input capacitance to
the supply rails.
Any of you lot tried measuring negative supply current with one of >>>>>> these things, or anything similar?
Thanks
Phil Hobbs
We're using a shunt resistor and an INA241 in one product. It claims >>>>> to work to -5 volts on the shunt. The product is in development
still, FPGAs and code and such, so I can't swear it works well.
Nice part. Of course it ought to be for $3. ;)
I can sell them to you for $2.
That "enhanced PWM rejection" part worries me slightly--sounds like it >>>> might have some kickout, which I really do not want. The 0.01% accuracy >>>> and CMR (166 dB!) are pretty cool though. I'll get a few to try out.
The PWM thing sounds like filtering or spike rejection. We're using it
in a barely-filtered 500 KHz 50-volt h-bridge output and the resulting
ADC noise is pretty good.
What bw do you need?
I'll email you our schematic.
Stay warm!
We'll need some "global warming" to do that.
Phil's likely to be a bit colder than me - I'm
near Long Island Sound, he's about 40 miles north.
Ed
Nah, not this time. Generally 50 uA - 5 mA per photodiode. It's a
Our current is bipolar so zero current parks the INA output halfway
up.
I'm using a 10-amp Hall chip on another product and it seems to be
nice. You may be running nanoamps.
differential laser noise canceller with some nice comfort features.
I ordered some of these to try out:
?ZXCT213CDW
?INA241A2IDDFR?
MCP6C04T-020E/CHY?
MCP6C26T-050E/LTY?
ZXCT181QA1W6
Should be here in the depths of the deepfreeze next week. We'll see!
Cheers
Phil Hobbs
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
Around here, survival gear is a sweat shirt, socks optional.
john larkin <jl@glen--canyon.com> wrote:
On Thu, 22 Jan 2026 21:30:04 -0500, ehsjr <ehsjr@verizon.net> wrote:So?s sunscreen. ;)
On 1/22/2026 5:37 PM, john larkin wrote:
On Thu, 22 Jan 2026 16:56:51 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
On 2026-01-22 14:33, john larkin wrote:
On Thu, 22 Jan 2026 12:11:09 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
Hi, all,
I'm designing a gizmo that needs current monitoring inside
bootstrap loops, with the sense resistors near the +- supply rails. >>>>>>> I want to get good PSR without using choppers, because I don't
trust them to have low enough kickout.
There are lots of nice chips for the positive rail, mostly 5V with >>>>>>> a wide CM range and costing eleven cents (positively Joergesque). >>>>>>>
However, none of them allows operation more than epsilon below
their ground reference (-0.1V or so). Thus the chip's supplies
would have to be VEE+5V to VEE, and it would produce an output down >>>>>>> near the negative rail. Inconvenient.
So the thought is to use something like a ZVCT213
<https://www.diodes.com/assets/Datasheets/ZXCT21x.pdf> running from >>>>>>> VEE to +5, with its output reference pin grounded.
This looks like it should work, but in the circs I'm going to have >>>>>>> to try it out first--I care about stuff like input capacitance to >>>>>>> the supply rails.
Any of you lot tried measuring negative supply current with one of >>>>>>> these things, or anything similar?
Thanks
Phil Hobbs
We're using a shunt resistor and an INA241 in one product. It claims >>>>>> to work to -5 volts on the shunt. The product is in development
still, FPGAs and code and such, so I can't swear it works well.
Nice part. Of course it ought to be for $3. ;)
I can sell them to you for $2.
The PWM thing sounds like filtering or spike rejection. We're using it >>>> in a barely-filtered 500 KHz 50-volt h-bridge output and the resulting >>>> ADC noise is pretty good.
That "enhanced PWM rejection" part worries me slightly--sounds like it >>>>> might have some kickout, which I really do not want. The 0.01% accuracy >>>>> and CMR (166 dB!) are pretty cool though. I'll get a few to try out. >>>>
What bw do you need?
I'll email you our schematic.
Stay warm!
We'll need some "global warming" to do that.
Phil's likely to be a bit colder than me - I'm
near Long Island Sound, he's about 40 miles north.
Ed
Nah, not this time. Generally 50 uA - 5 mA per photodiode. It's a
Our current is bipolar so zero current parks the INA output halfway >>>>>> up.
I'm using a 10-amp Hall chip on another product and it seems to be >>>>>> nice. You may be running nanoamps.
differential laser noise canceller with some nice comfort features.
I ordered some of these to try out:
?ZXCT213CDW
?INA241A2IDDFR?
MCP6C04T-020E/CHY?
MCP6C26T-050E/LTY?
ZXCT181QA1W6
Should be here in the depths of the deepfreeze next week. We'll see! >>>>>
Cheers
Phil Hobbs
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
Around here, survival gear is a sweat shirt, socks optional.
Cheers
Phil Hobbs
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