On Tue, 27 Sep 2016 11:34:26 -0700 (PDT), whit3rd <whit3rd@gmail.com> wrote:>On Tuesday, September 27, 2016 at 11:10:13 AM UTC-7, George Herold wrote: >> On Tuesday, September 27, 2016 at 12:45:44 PM UTC-4, John Larkin wrote: >> > I want to measure some power rail currents on a PC board, part of >> > self-test, and it looks like I could use a shunt resistor and an >> > INA199. >> > >> > http://www.ti.com/lit/gpn/ina199 >> > >> > It's fairly cheap and second-sourced by ON. > >> So you can power it from 3V and sense currents on a 26V rail.... >> How's it do that? > >Unlike most instrument ampllifiers, this one doesn't buffer the inputs; >it takes circa 26 uA input current, through dropping resistors. >In some sense, this gives it low input impedance (but not when applied >across a resistor measured in milliohms). > >I presume they laser-trim the resistances, to get good common-mode >rejection. It would be difficult to match its performance with loose parts.Beware. Some of these INAxxx devices actually run flying-switch mode, thus have a slight delay between current change and output response. And I've seen complaints that the Spice models don't work with LTspice. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 |
current monitor
Started by ●September 27, 2016
Reply by ●September 28, 20162016-09-28
Reply by ●September 28, 20162016-09-28
On Wed, 28 Sep 2016 07:39:59 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:>On Tue, 27 Sep 2016 11:34:26 -0700 (PDT), whit3rd <whit3rd@gmail.com> >wrote: > >>On Tuesday, September 27, 2016 at 11:10:13 AM UTC-7, George Herold wrote: >>> On Tuesday, September 27, 2016 at 12:45:44 PM UTC-4, John Larkin wrote: >>> > I want to measure some power rail currents on a PC board, part of >>> > self-test, and it looks like I could use a shunt resistor and an >>> > INA199. >>> > >>> > http://www.ti.com/lit/gpn/ina199 >>> > >>> > It's fairly cheap and second-sourced by ON. >> >>> So you can power it from 3V and sense currents on a 26V rail.... >>> How's it do that? >> >>Unlike most instrument ampllifiers, this one doesn't buffer the inputs; >>it takes circa 26 uA input current, through dropping resistors. >>In some sense, this gives it low input impedance (but not when applied >>across a resistor measured in milliohms). >> >>I presume they laser-trim the resistances, to get good common-mode >>rejection. It would be difficult to match its performance with loose parts. > >Beware. Some of these INAxxx devices actually run flying-switch mode, >thus have a slight delay between current change and output response. > >And I've seen complaints that the Spice models don't work with >LTspice. > > ...Jim ThompsonFlying _capacitor_, switch driven :-[ ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 |
Reply by ●September 28, 20162016-09-28
John Larkin wrote...> > .. I could use a shunt resistor and an INA199. >http://www.ti.com/lit/gpn/ina199 > > It's fairly cheap and second-sourced by ON.What's the ON Semi part number? -- Thanks, - Win
Reply by ●September 28, 20162016-09-28
On Wednesday, September 28, 2016 at 10:43:03 AM UTC-4, Jim Thompson wrote:> On Wed, 28 Sep 2016 07:39:59 -0700, Jim Thompson > <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: > > >On Tue, 27 Sep 2016 11:34:26 -0700 (PDT), whit3rd <whit3rd@gmail.com> > >wrote: > > > >>On Tuesday, September 27, 2016 at 11:10:13 AM UTC-7, George Herold wrote: > >>> On Tuesday, September 27, 2016 at 12:45:44 PM UTC-4, John Larkin wrote: > >>> > I want to measure some power rail currents on a PC board, part of > >>> > self-test, and it looks like I could use a shunt resistor and an > >>> > INA199. > >>> > > >>> > http://www.ti.com/lit/gpn/ina199 > >>> > > >>> > It's fairly cheap and second-sourced by ON. > >> > >>> So you can power it from 3V and sense currents on a 26V rail.... > >>> How's it do that? > >> > >>Unlike most instrument ampllifiers, this one doesn't buffer the inputs; > >>it takes circa 26 uA input current, through dropping resistors. > >>In some sense, this gives it low input impedance (but not when applied > >>across a resistor measured in milliohms). > >> > >>I presume they laser-trim the resistances, to get good common-mode > >>rejection. It would be difficult to match its performance with loose parts. > > > >Beware. Some of these INAxxx devices actually run flying-switch mode, > >thus have a slight delay between current change and output response. > > > >And I've seen complaints that the Spice models don't work with > >LTspice. > > > > ...Jim Thompson > > Flying _capacitor_, switch driven :-[Ahh OK... I didn't read all that much but I saw nothing in the spec sheet about flying capacitors. (it did mention zero drift topology.) I'd think that would mean a limit on the differential input voltage. (but it's listed as -26 to +26.) George H.> > ...Jim Thompson > -- > | James E.Thompson | mens | > | Analog Innovations | et | > | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | > | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | > | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | > | E-mail Icon at http://www.analog-innovations.com | 1962 |
Reply by ●September 28, 20162016-09-28
On Wed, 28 Sep 2016 09:57:06 -0700 (PDT), George Herold <gherold@teachspin.com> wrote:>On Wednesday, September 28, 2016 at 10:43:03 AM UTC-4, Jim Thompson wrote: >> On Wed, 28 Sep 2016 07:39:59 -0700, Jim Thompson >> <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: >> >> >On Tue, 27 Sep 2016 11:34:26 -0700 (PDT), whit3rd <whit3rd@gmail.com> >> >wrote: >> > >> >>On Tuesday, September 27, 2016 at 11:10:13 AM UTC-7, George Herold wrote: >> >>> On Tuesday, September 27, 2016 at 12:45:44 PM UTC-4, John Larkin wrote: >> >>> > I want to measure some power rail currents on a PC board, part of >> >>> > self-test, and it looks like I could use a shunt resistor and an >> >>> > INA199. >> >>> > >> >>> > http://www.ti.com/lit/gpn/ina199 >> >>> > >> >>> > It's fairly cheap and second-sourced by ON. >> >> >> >>> So you can power it from 3V and sense currents on a 26V rail.... >> >>> How's it do that? >> >> >> >>Unlike most instrument ampllifiers, this one doesn't buffer the inputs; >> >>it takes circa 26 uA input current, through dropping resistors. >> >>In some sense, this gives it low input impedance (but not when applied >> >>across a resistor measured in milliohms). >> >> >> >>I presume they laser-trim the resistances, to get good common-mode >> >>rejection. It would be difficult to match its performance with loose parts. >> > >> >Beware. Some of these INAxxx devices actually run flying-switch mode, >> >thus have a slight delay between current change and output response. >> > >> >And I've seen complaints that the Spice models don't work with >> >LTspice. >> > >> > ...Jim Thompson >> >> Flying _capacitor_, switch driven :-[ > >Ahh OK... I didn't read all that much but I saw nothing in the spec sheet about >flying capacitors. (it did mention zero drift topology.) > >I'd think that would mean a limit on the differential input voltage. >(but it's listed as -26 to +26.) > >George H. >> >> ...Jim Thompson[snip] If you examine the Spice model you'll see the switching. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 |
Reply by ●September 28, 20162016-09-28
On Tue, 27 Sep 2016 09:45:42 -0700, John Larkin <jjlarkin@highlandtechnology.com> wrote:>Any thoughts?An alternative could be the Hall effect sensors from Allegro. They are more expensive, but you won't need a shunt resistor, and you get galvanic isolation. http://www.allegromicro.com/en/Products/Current-Sensor-ICs.aspx -- RoRo
Reply by ●September 29, 20162016-09-29
On 28 Sep 2016 09:52:37 -0700, Winfield Hill <hill@rowland.harvard.edu> wrote:>John Larkin wrote... >> >> .. I could use a shunt resistor and an INA199. >>http://www.ti.com/lit/gpn/ina199 >> >> It's fairly cheap and second-sourced by ON. > > What's the ON Semi part number?NCS199. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●September 29, 20162016-09-29
On Wed, 28 Sep 2016 22:45:27 +0200, Robert Roland <fake@ddress.no> wrote:>On Tue, 27 Sep 2016 09:45:42 -0700, John Larkin ><jjlarkin@highlandtechnology.com> wrote: > >>Any thoughts? > >An alternative could be the Hall effect sensors from Allegro. They are >more expensive, but you won't need a shunt resistor, and you get >galvanic isolation.They also have GMR detectors that are more sensitive and lower noise. They're still pretty noisy, though.> >http://www.allegromicro.com/en/Products/Current-Sensor-ICs.aspx
Reply by ●September 29, 20162016-09-29
Jim Thompson wrote...> > If you examine the Spice model you'll see the switching.Given the 5uV typical offset spec, there must be some kind of chopper / auto-zero activity. And they admit or claim as much. Often this manifests itself in spectral noise measurements, but nothing shows for this part up to 100kHz. Autozero activity is different from flying capacitors, and wouldn't imply time delays over the 80 - 100kHz bandwidth. -- Thanks, - Win
Reply by ●September 30, 20162016-09-30
"krw" wrote in message news:v3iqubllq8r54d793ccr9v6r5jp08nk1kr@4ax.com...> They also have GMR detectors that are more sensitive and lower noise. > They're still pretty noisy, though. > >> http://www.allegromicro.com/en/Products/Current-Sensor-ICs.aspxYou might also consider an analog Hall effect sensor you can glue to a PCB over a track. Less than a dollar: http://www.mouser.com/ProductDetail/Texas-Instruments/DRV5053EAQLPGM Paul
