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current monitor

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  current monitor John Larkin <jjlarkin@highlandtechnology.com> - 2016-09-27 09:45 -0700
    Re: current monitor Syd Rumpo <usenet@nononono.co.uk> - 2016-09-27 18:09 +0100
    Re: current monitor Winfield Hill <hill@rowland.harvard.edu> - 2016-09-27 10:17 -0700
    Re: current monitor George Herold <gherold@teachspin.com> - 2016-09-27 11:10 -0700
      Re: current monitor whit3rd <whit3rd@gmail.com> - 2016-09-27 11:34 -0700
        Re: current monitor rickman <gnuarm@gmail.com> - 2016-09-27 18:49 -0400
        Re: current monitor Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2016-09-28 07:39 -0700
          Re: current monitor Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2016-09-28 07:42 -0700
            Re: current monitor George Herold <gherold@teachspin.com> - 2016-09-28 09:57 -0700
              Re: current monitor Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2016-09-28 10:01 -0700
                Re: current monitor Winfield Hill <hill@rowland.harvard.edu> - 2016-09-29 12:42 -0700
    Re: current monitor papabear546@gmail.com - 2016-09-27 14:17 -0700
      Re: current monitor John Larkin <jjlarkin@highlandtechnology.com> - 2016-09-27 16:36 -0700
    Re: current monitor Johann Klammer <klammerj@NOSPAM.a1.net> - 2016-09-28 00:38 +0200
    Re: current monitor Reinhardt Behm <rbehm@hushmail.com> - 2016-09-28 11:21 +0800
    Re: current monitor Winfield Hill <hill@rowland.harvard.edu> - 2016-09-28 09:52 -0700
      Re: current monitor John Larkin <jjlarkin@highlandtechnology.com> - 2016-09-28 20:44 -0700
    Re: current monitor Robert Roland <fake@ddress.no> - 2016-09-28 22:45 +0200
      Re: current monitor krw <krw@nowhere.com> - 2016-09-29 13:00 -0400
        Re: current monitor "P E Schoen" <paul@pstech-inc.com> - 2016-09-30 18:32 -0400
          Re: current monitor Winfield Hill <hill@rowland.harvard.edu> - 2016-09-30 18:53 -0700
            Re: current monitor Neon John <no@never.com> - 2016-10-01 10:30 -0400
              Re: current monitor Winfield Hill <hill@rowland.harvard.edu> - 2016-10-01 09:13 -0700
                Re: current monitor Klaus Kragelund <klauskvik@hotmail.com> - 2016-10-02 14:07 -0700
                  Re: current monitor klaus.kragelund@gmail.com - 2016-10-02 14:54 -0700
            Re: current monitor rickman <gnuarm@gmail.com> - 2016-10-01 10:33 -0400
              Re: current monitor "P E Schoen" <paul@pstech-inc.com> - 2016-10-02 00:01 -0400

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#429491 — current monitor

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.

Any thoughts?

 

-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

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#429495

On 27/09/2016 17:45, 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.
>
> Any thoughts?

I've used several in that series, if not that particular device. 
Nothing to report - they work just fine.  Obviously you know about 
Kelvin connections.

Cheers
-- 
Syd

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#429496

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.

 I like the ltc6101, 02 ... series.


-- 
 Thanks,
    - Win

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#429501

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.
> 
> Any thoughts?
So you can power it from 3V and sense currents on a 26V rail.... 
How's it do that?  

George H. 
> 
>  
> 
> -- 
> 
> John Larkin         Highland Technology, Inc
> 
> lunatic fringe electronics

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#429504

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.

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#429540

On 9/27/2016 2:34 PM, whit3rd 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.

The dropping resistors don't drop much.  The amp has gain which means 
the feedback and reference resistor are much larger than the input 
resistors.  These values are nominally 5 k and 1 Meg.  So the common 
mode voltage on the inputs to the internal amp would be about 99.5% of 
the input voltage to the chip.  See fig 22 in the data sheet.

-- 

Rick C

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#429637

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     |

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#429638

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 :-[ 
		
                                        ...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     |

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#429662

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     |

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#429663

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     |

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#429834

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

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#429528

On Tuesday, September 27, 2016 at 11:45:44 AM UTC-5, John Larkin wrote:
>
> Any thoughts?
> 
> John Larkin         Highland Technology, Inc

We use the Maxim MAX4080SASA+. It works great and unlike some Maxim parts, has always been readily available from multiple distributers.

We use two of them across the same sense resistor for battery charging / discharging current measurements.

I post this mostly for others because I know you won't use Maxim (and I completely understand why).

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#429547

On Tue, 27 Sep 2016 14:17:46 -0700 (PDT), papabear546@gmail.com wrote:

>On Tuesday, September 27, 2016 at 11:45:44 AM UTC-5, John Larkin wrote:
>>
>> Any thoughts?
>> 
>> John Larkin         Highland Technology, Inc
>
>We use the Maxim MAX4080SASA+. It works great and unlike some Maxim parts, has always been readily available from multiple distributers.
>
>We use two of them across the same sense resistor for battery charging / discharging current measurements.
>
>I post this mostly for others because I know you won't use Maxim (and I completely understand why).

The INA199 can do bipolar current sensing, if you bias its output Vref
pin above ground. And there's a second source!




-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

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#429539

On 09/27/2016 06:45 PM, 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.
> 
> Any thoughts?
> 
>  
> 
some rails(3.3) have really high currents. 
esp MBs from before they started using POL regulators running off 12V.
you'll need relatively small resistors. 

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#429573

AT Wednesday 28 September 2016 00:45, 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.
> 
> Any thoughts?

If you need it digitized you can use the PAC1720 from Microchip/SMSC, 1.60$ 
from DK.
It has two bidirectional channels, measures current and voltage up to 40V. 
Interface is I2C.

-- 
Reinhardt

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#429660

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

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#429769

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 

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#429701

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

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#429828

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

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#429983

"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.aspx

You 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 

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