current monitor

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

I like the ltc6101, 02 ... series.

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

George H.

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.

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).

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.

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.

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

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.

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

What's the ON Semi part number?

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.

If you examine the Spice model you'll see the switching. ...Jim Thompson

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.

NCS199.

They also have GMR detectors that are more sensitive and lower noise. They're still pretty noisy, though.

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.

You might also consider an analog Hall effect sensor you can glue to a PCB over a track. Less than a dollar:

Paul