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 

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

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

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

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.

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).

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. 

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

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

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